Tuesday, 14 March 2017

CZE T251 FM Broadcast transmitter REVIEW

This is an overlook and general impressions review of the Chinese made CZE T251 FM Broadcast transmitter. I ordered mine from eBay from seller 'Thanksbuyer-hobby' for $219,- including shipping. It took 11 days to arrive which is fast!

Normal operation:
You switch on by pressing the on/off button at the back. Then you get either the standby screen or the transmit screen, depending on how the transmitter was set when it was last switched off. If you press the front dial for more than one second the transmitter goes into sleep mode and won't transmit. The button will light up red. A simple short press of the front dial button awakes it and powers it up. The button now lights up blue.
Here are some pictures to illustrate this:




In transmit mode the display shows, from top left to right: the frequency it's transmitting on, the audio volume (goes from 0 to 79, you can see in the picture above the audio is set to the maximum 79) and whether it's stereo or mono (one or two speakers displayed) and the microphone level (also from 0 to 79, M00 means microphone level is set at minimum). The row underneath shows the RF power output, the SWR reading and the temperature of the power transistor. When transmitting, turning the front dial regulates the output audio volume of the transmission. You can access the menu while transmitting and change settings without the transmission being disturbed but if you change the RF frequency, the transmission will stop.

The Menu consists of the following items:
1 - Frequency set
2 - Audio Volume
3 - Microphone Volume
4 - RF Power set
5 - Stereo or Mono
6 - Temperature Alarm set
7 - SWR Alarm set
8 - Mute
9 - Exit Menu
If you turn the dial clockwise you go through the menu from item 1 to 9. If you turn counter-clockwise you go through the menu from item 9 to 1.

Things to be aware of:
First thing to be aware of when you buy this transmitter without a power supply is that it needs a 2.5mm inner diameter/5.5mm outer diameter DC barrel connector. Not the standard 2.1/5.5mm ones that are used with, for instance, the CZE/7C. The correct procedure to switch this unit off is to first press the button at the front to put it in sleep mode. If the fan is running when you switch off like this, it will keep running for a short while (about 20 seconds, give or take) and then, when the fan stops running, you can switch the unit off by pressing the on/off button at the back. If you switch off following this procedure, the unit will always start up in sleep mode. This prevents it from immediately transmitting when switched on. A simple short press of the front dial button will then start the transmission. The RF power will start rising smoothly to the set output power and will reach that power level within a maximum of approximately 10 seconds.
Here are two pictures of the backside:



Also something to be aware of is that this unit has as standard an N-type RF output socket (female). I screwed an adapter plug (N-male to SO239) onto the antenna output socket to change it into an 'SO-239' because I only use 'PL-259' plugs on my coax.
If you look closely at the top two pictures you can see, I made two little extensions (from some Ø15mm copper tubing) for the front feet so the transmitter stands a little higher. The air intake is underneath and at the front so it's best to put the transmitter a bit higher on its feet to give it some space to breathe in air. If you don't do this the front panel almost touches the surface with the main body clearance being 4.5mm. On YouTube I've seen a few other users of this unit do the same thing. You don't HAVE to do this as long as the unit stands on a smooth flat surface.
Before owning this transmitter I had used the CZE-7C, 7 Watt transmitter and I must say I liked it a lot. Even-though many reviews complain about the sound quality of the CZE 7C, on my car radio it sounded pretty good but the T251 sounds even better! Anyway, it's good to have a CZE 7C handy. In my case I use it to test the bandwidth of my antenna and of Low Pass filters I build etc. So I sort of use it as a signal generator, because you can change frequency real easy whilst transmitting. That is something the T251 will not do! If you go into the menu to change the frequency, the RF stage switches off. Btw, I noticed that if you put the T251 in sleep mode after it has been transmitting it still transmits a very weak signal. It can't be more than a few micro Watts but I can still hear the music buried in noise on my radio. Probably the FM chip that still gets power from electrolytic-capacitors that haven't discharged yet.
The FM chip:
I used to think this transmitter was equipped with the BH1414K FM-chip but I inquired with the seller and they informed me that it has the BH1415F chip inside. This was a disappointment for me, because for the price I thought it would have the much better BH1414K, but still, it does a pretty good job. Of course it's not only the chip itself that is important. It's also the circuitry around it, and there is a distinct difference between the signal from this transmitter and the signal from the cheaper ones which also use the BH1415F like the CZE 7C. That's mostly due to the end-stage with it's filters and power transistor. The RD30HVF1 mosfet is an excellent and robust transistor for the end stage. However, it is noted in the comments below that the BH1415F chip can cause some overload issues that result in stations near to the transmitting frequency being overpowered by the CZE's signal for about a maximum of half a mile around the transmitter location. So be aware of that. It's not perfect (obviously).
Frequency stability is rock solid and stays well within the advertised maximum deviation of 10Hz.
Of course you can analyse the signal from this transmitter until you're blue in the face and it's never going to be as good as a professional Broadcast transmitter but that is reflected in the price.
Here is a picture of the output sinewave at 5 Watt RF power on an oscilloscope. As you can see a nice clean signal.



Pre-emphasis delay is 50µSec and can not be changed in the menu. So this transmitter is not aimed at the American market.  You will just have to contact the seller and ask if they have units with 75µSec pre-emphasis delay if you live in the United States. USA Stock is regularly promoted from different sellers on eBay. (I had a link here to some USA stock on eBay but the listing has ended.)
This transmitter has an RS232 connection at the back, underneath the N-Connector but don't think you can control this unit with your PC. That connection is only for debugging and firmware updates.
Don't assume either that the extra 18 Watts of power compared to the CZE 7C is going to increase your range significantly with the same antenna setup. It's not. You want bigger range? Put your antenna up higher. This set gives me just a little bit more range than the CZE 7C with the same open dipole antenna that I use and the signal is a bit stronger within the normal range but it's only a very small improvement. Believe me, like with an audio system, the quality of the speakers is everything, so it is with antennas and especially their height. (I address the point of 'range vs power' at the bottom of this review also.) As a rule, to double your range with the same antenna set-up, you need a 10 fold increase in output power!!

A closer look at the signal:
Alas I don't have expensive spectrum analyzers etc so here's a few screenshots of the signal from my Software Defined Radio (SDR) on my computer (click on the picture to get full screen view):

Stereo transmit signal at 25 Watts:



This is the signal from a professional local FM radio station whose transmitter and antenna are located just 100 meters from my house. Compare this signal to the previous picture of the T251. Pretty similar right?


Btw, if you look at the signal to noise ratio (SNR) you can see that it is a bit lower on the T251 than on the professional transmitter but that changes with the type of music. If there's a low volume bit in the music the SNR on the T251 can go as high as 37dB. Btw, that is SNR measured with this SDR receiver. That's not exactly a precision instrument. The real Signal to noise ratio is advertised as being equal to or above 70dB. And in fact, CubicSDR software indicates a SNR between 65 and 70dB so that is excellent. These numbers I mentioned are for the stereo transmissions. When you transmit in mono, the signal to noise ratio will be even higher and the mono transmissions also have a longer range than the stereo transmissions.

Mono signal:


Stereo signal but no audio input:



Signal comparison between the CZE-7C (7 Watt transmitter) and the CZE-T251 with the same song playing, both in stereo and both audio volumes and output power set to the same level. Note the difference in deviation beyond the 200kHz bandwidth and the more slender signal of the T251:

This is the CZE-7C. You can see in the waterfall display that the audio bleeds over the 200kHz bandwidth limit, causing disruption on the adjacent frequencies. You can also see that the signal is quite wide:



This is the CZE-T251, here you can see the audio stays nice and tight within the 200kHz bandwidth limit, like a good transmitter should do. The signal is also much more slender than that of the 7C:



Here are some screenshots done with "CubicSDR" software:

Signal at 25Watt without modulation. You can see the 19kHz stereo pilot-tone and more in the upper right audio spectrum graph:



Signal with normal music. Again note the audio graph in the upper right-hand corner:


This is an illustration of how the audio signal produced by an FM stereo transmitter is build-up and how it occupies the frequency spectrum:


You can find more on the technicalities of FM Broadcasting on Wikipedia.

More observations about the T251:
The transmitter is very well built. It's all thick Aluminium. There's no plastic on it anywhere except for the on off switch at the back. Even the dial knob at the front is made from Aluminium. It is a lot smaller in size then I expected from the pictures on eBay though. Be prepared for that. The size is: front-panel width: 173mm (6.81") x front-panel height: 58mm (2.28") x depth: 210mm (8.27"). Main-body width: 167mm (6.57"). Main-body height: 53mm (2.09")
The power amplifier part (end stage) is mounted to a big heat sink with ribs that go all the way to the side of the case and with a fan attached to one side which blows air over it. This is more than adequate to keep the temperature down. (More on the fan in the item below.)
The transmitter is equipped with a temperature alarm. If the temperature gets higher than the alarm setting the unit will stop transmitting and an alarm will sound.  I have set mine to 50°C. The power transistor can easily take 120°C according to the spec sheet but the fan keeps the transistor at a maximum of 39°C so if the temperature rises above that, then it's obvious that there's something wrong and in that case the sooner the unit switches off, the better.
The unit also has a build in SWR meter with a programmable SWR alarm setting. If the alarm is triggered the unit stops transmitting immediately and an alarm will sound continuously until you switch the unit off. If you then switch on again the RF power output has automatically changed to 1 Watt. This is obviously a safety measure in case there's still something wrong with your antenna system. If all is well, you can go into the menu and set the power to your desired value. The SWR meter is a bit optimistic. It says 1.0 when it is really 1.1 but that's no problem in normal use.
The power transistor used is the RD30HVF1 mosfet rated at 30 Watts. It has a typical efficiency of 60% (meaning 60% of the energy put in is transferred to RF power, the rest to heat) and can take an SWR mismatch of 20 to 1 without being destroyed (!!!) The temperature sensor is mounted near the mosfet and is of the LM35 centigrade type. Both the sensor and the power transistor are generously covered in a heat conducting paste as you can see in the pictures in the link below. In use with a voltage of 12.55 Volts I draw about 3.37 Amps at the full 25 Watt RF-power setting, so that is 42.29 Watts. (this is measured without the fan running) So that results in an efficiency of 59,11%, almost exactly the rated efficiency of the power transistor which was, as I mentioned earlier, 60%.
The chip that controls the display and remembers the settings is the 12C5A.
You can set the input audio volume electronically from 0 to 79 and the same for microphone input. Beware that you need a dynamic microphone and NOT an electret type microphone!! The microphone input is a mono channel (6.3mm jack plug needed). But using a microphone directly connected to the transmitter isn't very practical, unless you're transmitting at a public event or something. Otherwise I would use a microphone connected to an audio mixer and connect that to the audio input of the T251. Audio input sensitivity is a bit less than on the CZE 7C. The input level is rated at ≤-15 dBV. The frequency response is: 50Hz to 15kHz (3dB). Distortion is 0.2% and the channel separation is 45dB (The channel separation of the average tuner/receiver is about 35dB so the transmitter is well above that.) I use a Philips MP3 player and I have its volume set all the way up and the same on the transmitter (volume to 79) and that get's the music exactly to the level of other stations. But it's better to use a pre-amplifier for the music, like a headphone amplifier or the line-out from an audio mixer to give yourself some leeway. I pre-record my programs and then run it through Adobe Audition which has a very good compressor plug-in by iZotope with a 'Broadcast' preset. That's what I use to render the radio show out and then transfer it to my MP3 player for broadcast. This works very well and the music quality is great. This unit has very tight bass and crisp highs. The sound of the 7 Watt CZE-7C is phatter in the lows and just doesn't reach the quality of the T251. Audio input is in the form of RCA connectors at the back of the unit. In the transmitter menu you can choose between stereo and mono transmission and it is my experience that the mono signal gives you a much bigger range.

More on the cooling fan:
The cooling fan kicks in automatically when the temperature reaches 39°C (102 F) and switches off again when the temperature drops to 35°C (95 F). It also starts running if you enter the menu to change settings. I guess this is done as a quick test to see if the fan is working. The fan produces no extra noise in the audio but it does produce a loud noise of itself so you don't want this transmitter near your microphone. Your studio must be in an other room than the transmitter or you'll hear the fan running in the background. You could of course replace the fan by a more silent one. It's not difficult to remove. The dimensions of the fan are: 40mm high x 40mm wide and 15mm thick. The hole spacing is 32mm. The fan get's 11,0 Volts when the transmitter is fed with 12,0 Volts. The fan's power cable has a 3 pin connector on it of which only the outer two are used. The middle pin is not connected. So if you get a replacement fan with a 2 pin connector you could just cut it off and solder the wires directly to the wires of the connector in the transmitter. The fan draws a current of 118 milliAmps at 11 Volts.
Fan Replacement Test:
I ordered some cheap silent fans from eBay and ran some tests. The first fan I tested was 40x40x10mm 12V 0.08 Amp. and this was totally not up to the job. It could not get the temperature down and kept running all the time. The second one I tested had a thickness of 15mm and a current draw of 0.1 Amp. It could get the temperature down enough to make it switch off again but only for the first 15 minutes. After that the heatsink was fully warmed up and too warm for this fan and it couldn't get the temperature down to where the fan would switch off again. So I reinstalled the old fan. So if you plan on replacing the fan you will need a type that is 40x40x15mm and with a minimum current draw of 150 milliAmps at 12 Volts. This is a picture of the fans I tested and which failed the test:



Here's a picture I took after the test, with the original fan again connected but not yet screwed into place. You can see the heat-sink arrangement and the 3 pin connector for the fan:


I couldn't actually find a good silent fan that was up to the job. Should you come across one that you tested and installed and which works good then I would appreciate it if you commented below with the link to where you got it. It would be a great help.

Range vs Power:
With the T251 set to stereo, the full 25 Watts output power and a dipole 7 meters off the ground and in free air but not clearing the rooftops (see picture of antenna below) and an SWR of 1.1 to 1, I get a range of 10 kilometers (6¼ Miles) in a small-town setting without high-rise buildings. (Nothing higher than 5 stories to block the signal). That is a 10 kilometer range in which the audio is noise free received on a car radio driving away from the transmitter location (receive antenna on the rear of the car roof, so the ground-plane formed by the car roof is pointing away from the signal)! The range in which the signal can still be received is about 15 to 20 kilometers (9 to 12½ Miles) depending on terrain and obstructions. If you put the antenna high enough to clear the rooftops of most buildings near you, that can easily double! I also did a test in which I set the transmitter to an output power of 1 Watt and tried what range I had. It was unbelievable. I still had a range of about 5 kilometers (3 Miles). Sure the signal broke up much faster behind obstructions like buildings and bridges but still. 5 Kilometers is not bad. As I mentioned I set the T251 to 1 Watt, but measured on my Diamond SX600 SWR/Power meter an output power of 1.75 Watt. But seeing as it has to go through 7 meters of RG213 and 2 meters of RG58 I recon the Effective Radiated Power (E.R.P.) couldn't have been more than 500mWatts. That's impressive and shows once more that the most important thing about a transmitter set-up is the height and placement (and build quality) of the antenna!! Height is everything!

Here's a picture of my home built dipole antenna:



If you want to have a look at the Printed Circuit Boards inside the transmitter, then I refer you to the link below to my Flickr page where you'll find an album with some closeups of the PCB's:
https://www.flickr.com/photos/ededitz/albums/72157679661456110

Troubleshooting:
Should you encounter any problems when operating this unit then there is an option you can try. If you switch the unit on with the switch at the back and at the same time keep the front dial button pressed in, the unit switches on into Self Test Mode. Here you can automatically check certain functions of the transmitter. Simply turn the dial to select the parameter you want to test and press to confirm. The unit then tests itself to see if it functions correctly. I personally have not tried this option yet because my unit functions perfectly and I am not comfortable doing this procedure when it's not necessary so I can't tell you exactly what it does when you select this option but just know that it is available should you need it.

This transmitter has one weird quirk. If you turn the front dial button whilst the unit is in sleep mode, with the button lit up red, or even if the unit is totally switched off, the temperature alarm can go off if you switch it on again! If this happens simply press the front dial button twice or switch off and on and you're good to go. A minor thing. Just don't play with the knob when it's switched off.

I've been getting some feedback that the output power is not really 25 Watt but more like 21 Watt. I myself measured this too on my SX600 SWR/Power meter but I thought it was my meter that was at fault; but I'm hearing from more people that they get the same measuring results. Now 4 Watt isn't a lot when you're already outputting 21 Watts so I shouldn't let it influence you if you're thinking about buying one of these units but I want this to be as honest a review as possible so I thought I would just mention it here.

On that note there is one more thing I must mention. A very small percentage of these units can fail and give a reading of zero output power and the SWR indicates 9.9 even though they go through quality control and are tested for a period of time before being sold. If that happens your only option is to contact the seller and try and get a new unit or a refund. The chances of this happening are extremely small but they are not 0%. Like anything you order from China there is a small gamble involved but usually the seller is very quick to replace the unit for you. It has happened to one person commenting below so you should be aware of this. But it is the first mention I received in the 2 years that this article is now online.

Conclusion:
This is an excellent transmitter for the money. Certainly not a 'toy' as some people on YouTube like to say when they compare this to a $5000.- transmitter. That's like comparing apples to pears.
It simply is not a professional FM Broadcast transmitter but listening to it on your car radio no one is going to notice that!!! Stations that are 0.2 MHz or more away from your frequency won't be interfered with by your signal. And you don't need to be afraid of harmonic signals either. The Butterworth Low Pass Filter in the end stage suppresses that very effectively. But do be aware that around the direct vicinity of the transmitter location, stations can be surpressed by this unit. This is however only within a few hundred meters of the transmitters location and it's not always the case. It depends on the local situation of course and also on the quality of your antenna. The sound quality is amazing. As I mentioned before, the cheaper CZE 7C's sound is phatter and has a bit more bass in it than the T251. This unit sounds very crisp and clear with deep tight bass and crisp highs. Really excellent. Of course you must keep in mind that the perceived sound quality is first of all dependent on the quality of your receiver and audio system.
If you want to buy a Chinese FM transmitter, get this one (or the cheaper 15 Watt CZE-15B which does have the BH1414K chip inside and is PC-controllable.)
I would stay away from the 60 to 80 dollar 15 Watt ones like the NIOrfNIO or the ST-15B. They are cheaper for a reason. Their quality is not terrible but comparable with the CZE 7C I mentioned above. But certainly stay away from the cheap FM kits. They use the KT0803L chip which is the worst FM chip you can get. Their signal is a mess, you'll black out the TVs in a full block radius. Spend a few extra dollars and get the good stuff.


Here is a link to the USER MANUAL for the CZE T251 in PDF form:
Click here for User Manual PDF

Here is a link to the datasheet (PDF) of the RD30HVF1 Mosfet power transistor:
https://www.mitsubishielectric-mesh.com/products/pdf/rd30hvf1.pdf

If you have any questions about this transmitter that were not addressed in this review then do not hesitate to ask me in a comment and I will try to answer it to the best of my ability.
The comments below this article have grown to over 40 now and they are proving to be a great resource. Reading them will give you an idea of other peoples experience with this unit and how it compares with other ones. Please add your own comment below and tell me about your experiences with this transmitter or just what you thought of this review. I'd love to hear your point of view.

Disclaimer: The author does not accept any responsibility for actions and or alterations to equipment undertaken by anyone after reading this blog post. Anything you do, you carry the responsibility for.
Operating an FM broadcast transmitter without a licence is illegal in most countries, however, owning a transmitter but not using it as such is usually not illegal. Please check the laws of the country you live in to make sure you don't break any laws.

81 comments:

  1. Nice one Eddy, great review, i am definitely considering picking up one of these now!

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    1. Thank you! I'm glad you enjoyed this review. It's a great transmitter, you won't regret buying one!

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  2. Hey Eddie, question about FM transmitters. Is the SDA-15B 15watt transmitter the same as the CZE-15B. Just because they look alike from the outside does it mean their guts are the same period would like to know your opinion. Thank you

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    1. Yes, I think they are the same. I can not be a 100% sure but if there is a difference then it is only in the firmware. I know that there is a version of the 15B where you can choose the audio pre-emphasis between 50µSec and 75µSec. But I am 99% sure the inside of the transmitters are the same.

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  3. Hey Eddy, thank you for your opinion and comments on the CZE-15B. Have another question for you. What do you think about the Warner FMT 50L comparing it to the CZE-T501 is one of these Exciters really better than the other? Thank you in advance for your comments.

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    1. Well, I'm sorry but I have no hands on experience with either of these so I couldn't give you an authoritative opinion on either of them. But they look to me to be quite good units judging from appearance and build quality. But you should look into how the signal is generated. Do they have a single chip or a good quality oscillator to generate the FM signal. That's usually a pretty good indicator. Real pro transmitters don't use a FM chip to generate the signal. And see if it has MPX audio inputs. Pro units usually have those. Other than that I can't help you I'm afraid. Hope it helped you out :)

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    2. Can't find too much information on either units that would be from a reliable source. They both do have a BNC connector for audio input. Haven't found any information on how the FM signal is generated on either units. Guess I'll just have to keep doing some homework. Thanks for your input.

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    3. Both of the units t501 and the Warner 50L seem to be pretty similar. Both have a BNC connector for audio input. About the only difference I can see is that the Warner has right and left UV meter. Was just hoping that you might be able to give me some insight. I do appreciate your honesty not knowing really too much about either units.

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    4. Just looking to buy a good unit that's reliable and not one that I wish I didn't buy. Been there done that. Thanks again Eddy...

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    5. Yes, I had a look around for you too. Found the video on the Warner 30L and they showed the signal on a spectrum analyzer. I must say it looked pretty good. Nice slender carrier without visible spurious and harmonics and decent signal to noise ratio too. But that's as far as I got. Maybe you can write/email directly to the factories and ask for more specific info. You never know what you can get.

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    6. I think I'll do just that. I'll drop them an email. If you find any more information on either units or have something more to comment please post it. Thanks again Eddy you're the best

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    7. Will do. Thank you and good luck Chris! :)

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  4. Oh yeah one other thing Eddy. Bought a Hlly TX-30s. Not too happy with it. Looking for something better but staying around 50 Watts or less.

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    1. Yes the HLLY TX-30s. I have no experience with them but I can't help but think it's a ripoff of the CZE-T251. The only difference seems to be that the on/off switch is at the front. They even use the same power transistor. Why are you not happy with it exactly?

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    2. Bought the Hlly TX-30s used. Wasn't able to test it before I bought it. Had some problems.

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    3. Had a HLLY TX-30s that we used for a mobile operation. I broke it recently (anyone know where to get a replacement CZH-MOD1 mainboard?), and based on this review decided to take a chance on the CZE-T251 (which is due to arrive by the end of the week).

      A notable difference between this and the HLLY is that the HLLY uses the BK1414 instead of the 1415. The 1414 is a better chip, but the HLLY did have some issues. Notably noise. Even when I could get a clean source into the HLLY, there was always a groaning/thumping noise for a few seconds every few minutes. It wasn't very loud or overpowering, but still notable.

      Other than that, the HLLY was quite nice. Based on the different chip, not sure I can agree that it's a full-on ripoff. Spectrum was super clean. At max output, it really didn't have any notable spurs. With the antenna on the roof, our HackRF (notoriously easy to overload) was fine picking up other stations. Never had an issue with signal. Got out about 15 miles with an antenna only about 15 feet up and below the tree line. Granted, our location is up on a hill, but it still did quite well considering the thick vegetation it competes with prior to the hill. So my personal opinion is the HLLY isn't a bad choice, but with this being about half the price, I went with this instead. Once I receive it, I can post a better direct comparison between the two.

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    4. Ah thank you for your reply. This is very interesting. Like I mentioned I sort of guessed it was a full on rip off purely based on how it looked. I have never handled a HLLY myself and I didn't know the HLLY had the 1414 chip inside. That is indeed a much better chip. I do hope the CZE T251 lives up to your expectations compared to the HLLY. It certainly serves me well but I don't have dedicated measuring equipment. Do let me know in a comment how it turns out. It will be very interesting to know, also for other readers of this article. Thank you again for your comment!

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    5. After almost a week with the transmitter, I can give some useful notes. The fan in the HLLY more readily varied its speed. It ran notably warmer but was quite quiet.

      The sound quality on both has been outstanding. I give the slight edge to the CZE, very tight and clean sound, excellent noise floor. I'm feeding a preprocessed "soundsolution" feed into it, you'd be hard pressed to tell it apart from a commercial station. When I was DJing the first night, I kept forgetting that my headphones were plugged into the radio (with a slight delay due to the processing). It sounded absolutely amazing.

      One disappointment has been the frontend overload. With the HLLY, I could still pull in other stations without issue on my sangean ats-909x in my house. Not so with the CZE. For a few hundred feet in the car, fm takes a notable hit all across the band. If I had to make a guess, the 1415 is likely the culprit. I have a low pass filter at 110mhz, so I don't know how far up the issue would extend, but the HLLY didn't wipe out the whole band like that. Desensitized a bit, but not extreme. With the CZE, a strong local "mix" station 800khz away has almost half a mile of noise from the CZE, so its certainly something you'd want to keep in mind in a densely populated area. This thing is definitely more noisy than the HLLY in it's RF output.

      I can't directly compare coverage since the antenna is slightly lower and right next to a tree now (and slightly crooked now. This is all temporary, it's all getting moved behind the barn in a few weeks and getting a new "tower") but early reports indicate our coverage is roughly equivalent.

      Is this the best transmitter ever? Not by a longshot. But I'd the best in it's class? Might very well be. You'd be hard pressed to find a better transmitter within a hundred bucks of this thing with this power level. I don't regret this purchase whatsoever, excellent transmitter for the price.

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    6. Thanks very much for that feedback. That's very useful information. Shame about the overload of adjecent stations. I agree it's probably the 1415 that causes that but I'm glad you like the transmitter. For the money it's a very good unit I agree. :)

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  5. Eddy, I use a Comet 5/8 wave antenna, which works very well. I noticed that you prefer a dipole which, also, seems to work very well. The bonus feature being that the dipole seems to be a good deal smaller than the Comet. Would I be sacrificing anything by going with a dipole instead?

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    1. Hi John. I'm not quite sure but I did a bit of research and it seems that a 5/8th has slightly less gain than a dipole. I found this page comparing the two at 100MHz: https://www.w8ji.com/VHF%20mobile%20vertical.htm
      But I recon in normal use you are not going to see a significant difference if you use the same height for either antenna. I use the dipole because, like you said, it's nice and small and doesn't catch much wind. I live on the coast so it can be really windy here. I've build mine myself and it works perfectly. I get an SWR of 1.1 to 1 and a bandwidth of 6 MHz (of 1.5 to 1 or less).
      So to answer your question, no I do not think you'll be sacrificing any range of your signal by going with a dipole.

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    2. Let me correct myself here. I just see that the Comet has 3.4 dBi gain and a dipole I know has 2.15dBi so the dipole would theoretically give you less range but I still believe in practice you won't notice it. Those gain figures are not so important. What's important is the height of you antenna whether it's a 5/8th or a dipole. Height is everything.

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    3. As I thought. Thanks so much for your prompt and well informed reply. I live in a situation where an HOA dictates what I can and cannot put on my roof, so mine is in the attic. This placement makes it invisible and windproof, but I'm sure it hampers performance, somewhat. That being said, height IS king, and I don't have it! Thanks again!!

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    4. Ah, I had my antenna under the roof in the attic also for a long time and now that I have a dipole outside and checked out the difference I think the 'being indoors' attenuated the signal by about 80%. I got the same range with antenna indoors using 25Watts as I got with antenna outdoors using 4 Watts of power (at same antenna height indoors or outdoors). I have a concrete triangular wall at one end, the same but with a window on the other end and the sloping roof made of wood and ceramic tiles. So having the antenna indoors may dampen the signal more than you might think but of course you have the benefit of it not being visible and if the range is enough for you then why would you mount it outside? Anyway, glad you found my reply useful John! Good luck! :)

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  6. If it's any help, the roof is shingled and the top of the building is all wood. Maybe the next home will give me better options for my hobby. Thanks again, Eddy!!

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  7. I currently use a ELE-05B with a dipole at 27 feet and I live in a hilly forested river valley. West and South gets out fair and North and East very poor. Planning on lifting my antenna double, but need to strengthen signal with in the signal area. Would I do that with more power like this unit you speak of or another dipole to ad a bay to double gain.

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    1. The extra power will strengthen your signal withing the signal area but it won't be a dramatic increase. I think having 2 dipoles will be more effective.

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    2. Actually I think I would do both. More power and bigger antenna.

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  9. Hello thank for revew! i got one of this and sound very clear,now i am using a dipole but i also bought a Comet CFM 95 SL 5/8 antenna fm, may it could be better of dipole?

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    1. The Comet should be a bit better but I think the difference will be very small.

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  10. I have been looking at a couple of your stories and i can state really well done.
    Radio Denmark

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    1. Thank you very much! That is a great compliment. I'm so glad you liked what you read. I appreciate it very much. -Eddy-

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  11. Hi Eddy--Great job on the CZE T-251 FM transmitter review! It's much appreciated. Can you please tell me how long you have had yours now in operation? Has it been without any issues of any kind? And do you have any other info or experiences regarding this unit? Thank you very much! Mike

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    1. Hi Mike, I've had my unit for over a year now and never had any issues. It works just fine.

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    2. Thank you very much Eddy. Take care!

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    3. Oh, and Eddy. I meant to ask you something else within the text of my message above. Do you operate your transmitter on a 24/7 basis? Or, are you only on sporadically? If so, how frequently do you actually get on the air with this transmitter. I am curious as to this transmitter's robustness if/when operated on a consistent ongoing basis. Thank you for your time and response to my queries. Mike

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    4. I'm afraid I only use it sporadically. I'm not a licenced operator and the fines are pretty high here. ;) But I'm sure the unit could handle continuous use pretty well.

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  12. Thank you for a great indepth look at the unit . Purchased mine back august 2018. Its a great transmitter for the money. I followed your advice on settings etc. Works great. I am using a 5/8 th wave ground plane 10ft above house making tip height 34 or so ft above ground , 27 ft of good coxail cable, swr 1.1 my elevation is 1450 ft and can see 40 miles in 70 percent of a compass reading. I can run 20 watts and get some amazing distance, but i am more interested in 12 miles and this allows me to fill in shadow areas and penetrate some glass in houses. I power unit with my old 22amp gold star , and no interference or hum. I like the unit. Thank you again the info you provided was and is of great help. Andy

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    1. Thank you so much for that vote of confidence Andy! I really appreciate it. I wrote the review to give people the best possible info to help make their decision in buying a good transmitter. I'm glad it helped you out. Looks like you're at a superbe location for transmitting, being that high up. I'm not surprised you get excellent range out of this unit. :) Thanks for the feedback Andy!

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    2. Also i use a ramsey stero headphone booster i built from kit . All music runs into this and it perks all of it up, and then into a ramsey sgc1 stero gain controler, then into my mixing board, i also just below antenna i use a ramsey fm transmitter lowpass filter sma i also built from kit. It all works great. Thanks again Eddy. Andy

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    3. That sounds like a good setup. Yes the audio needs some amplification before it goes into the transmitter and using a headphone amp or a mixer is the best solution. Glad it all works so well Andy!

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  13. Hi Eddy.. You have provided some excellent information on the CZE T251 FM Broadcast transmitter.. I bought one about a year ago with absolutely no problems..I decided I wanted more power so I ordered the CZE 150 watt transmnitter..Could you please give me more information about the machine and does this machine use the same FM chip as the CZE T251..Thanks Garry Sigler Kelowna BC Canada.

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    1. Hi Gary, thank you for your feedback. I'm sorry but I have no experience with the 150 Watt model so I can't give you any information about it.

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  14. Hi Eddy..Thank you for the reply..I have searched everywhere for information on the CZH 150 watt transmitter however I would imagine that after being made by the same company the chip would be identical to the 25 watt CZH..Anyway where you are I widh you and your family a Happy New Near and all the best for the year 2019..Best Regards Garry Kelowna BC Canada.

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    1. Well, I'm not sure. Your guess is as good as mine. :) Happy newyear to you and your loved ones too Gary!

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  15. Hi Eddy..Yes the CZH 150 watt transmitter has a really great sound..The coax cable is twice as thick and the antenna is situated on the top of the house so I can cover around 20 miles..If I transmit full power will that shorten the life span of the transmitter or would it be better to use 50-75 percent of power to be on the safe side..I hope all is well..Garry Kelowna BC Canada.

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    1. Well I don't think that using it at full power shortens its lifespan. That used to be the case with the old vacuüm-tube transmitters but with solid state I don't think it's that much of an issue. However I would use it on 85 to 90% if I were you. Like you say, to be on the safe side :)
      Have you discovered yet what chip (if any) is used in the CZH 150? I would love to know.

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  16. Hey Eddy..Thanks for the quick reply..I did some research and the FM chip is the BH1414K..It has a built in PLL system circuit which acts sort of like a limiter..If you like I can send you a photo of the broadcast studio along with a schematic of the guts inside the transmitter..Just contact me at this email ..shawna.bellamy123@gmail.com..Also I'm live on the internet weekends 7.30-9.30 PM Pacific Standard time..All you have to do is type in Cougar Mix on Livesets.com..Check out my show..I think you may like it..I have worked for commercial radio stations in the past both small and major market AM radio stations..I am also in the process of applying for a broadcast licence to air legally..Hopefully the CRTC will grant me approval to offer a community oriented station involving local live and a variety music mix..Anyways I gotta run..Take care..Garry B Kelowna BC Canada

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  17. Ah sounds good. I would have been surprised if it didn't have the BH1414 chip inside. I'll check out your show and I'll send you an email. Good luck with the application for your broadcast licence. Sounds very exciting :)

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  18. I've got two of these and I'm having the same problem with both. My PO: is reading 0.0. if turned the wattage up and still nothing. My swr reads 9.9 and my temp is fine. I've used two different antennas and still when I power on the machines, they go back to the same readings. Could you tell me what might be wrong?

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    1. I'm afraid they're just broken. There's nothing you can do but contact the seller and ask for a replacement. I heard more people are having this problem. Some of these units can be faulty out of the factory.

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  19. Hi Eddy, i hope you are fine, I'm having the problem with my transmitter CZE T251. it shows PO: reading 0.0. if turned the wattage up and still nothing. My swr reads 9.9 and my temp is fine. I am using half wave dipole antenna , and when I power on the machine, it go back to the same readings PO:0.0 and SWR 9.9 . Could you tell me what might be wrong? i am worried about it.

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    1. Hi Anmjad. I'm afraid your unit has failed. I recognize the readings you mention and I don't think there is anything you can do. You must make contact with the seller and see if you can return the unit and get a new one or a refund. I'm sorry this happened, that really sucks.

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    2. I have included a section in the review mentioning the problem you have to warn people. I hope the seller will resolve this problem for you.

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    3. it can be an antenna problem? or unit expired confirmed so that i may contact to my seller.

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    4. Well, it could be an antenna problem, the way to check that is to attach a 50 Ohm dummy-load and see if the problem is still there.

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    5. what it means by a dummy-load?

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    6. A Dummy-Load is a 50 resistor that is the same as an antenna with SWR 1:1 You use it to test transmitters. Here's a link to an example of what I mean: https://www.ebay.com/itm/25W-N-male-connector-dummy-load-DC-3GHz-50ohm-free-shipping-termination-load/232119730019?hash=item360b69ff63:g:hBYAAOSwHMJYCI8R

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    7. Sir, I have contacted to my seller, he Replied me this message as below:
      Hi sir,
      Have a good day.
      I think the 25w FM transmitter Transistor RD30 is wrong.

      Did you heard warning,display "Please check the antenna" ?

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  20. Ah okay, well then you need to check the transistor. I would be very surprised if the transistor is faulty though. It's very strong. But let me know what happens.

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    1. hi Eddy, i opened the transmitter, its not having RD30HVF1, but its having different one RD35HUP2transistor in black colour. what is the problem with it? why its having a different one.

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    2. The RD35 is actually a bit better than the RD30 because it is 35 Watt and it is also more efficient (70% instead of 60% for the RD30) so it should easily be capable of delivering 25Watt power. That's why I can't believe it is broken.

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  21. Dear eddy, its looks repaired to me at transistor area, visit my transmitter inside pictures at flicker https://flic.kr/s/aHskUpNtvh Why it is different from yours?

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    1. Yes the soldering looks a bit weird but I don't have any answers for you. I don't know why that transistor is in there or if it is repaired.

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    2. Eddy, can i buy the complete RF kit with is attached with heatsink? is it available? if you know please tell me, if it will be availed then i will exchange the complete kit with new one.

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    3. I don't think you can buy a separate end stage like you say. I have never seen them for sale anywhere.

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  22. Current transistor on my chip is RD35HUP2 183AY-G5, but it is not available in market. I have found another one which is RD35HUP2 183AK-G5. can i install this one? the difference is that old one is 183AY-G5 and new is 183AK-G5. but both are RD35HUP2. I am confused about it, Please help.

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    1. Yes you should be able to use 183AK-G5 The important thing is that the type number is the same like RD35HUP2. So that should work yes.

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  23. hi eddy i purchased one of those transmitters and it only sticks itself at 1watt quite a signal though but not good enough any suggestions i have tried to email the seller to no avail thanks jim b

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    1. That is weird. Normally the seller will refund you. Maybe you can make a case against the seller, if you payed with paypal for instance

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  24. Hi Eddy. I've just read your article with interest. I am using a CZE-7C. Unfortunately I csnnot use the high power setting without it interfering with other equipment. I need to be able to record material through my mixer whilst the computer is playiing out music on air but the transmitter is bleeding through via my mic cable. It is worse when using a condenser mic.
    If I upgrade to the CZE T251 will this solve the problem? My studio in three floors up at the top of my house with the transmitter inside the window between two layers of double glazing. I cannot easily put another antenna on the roof without scaffolding.

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    1. Hi, well I don't think buying the T251 will solve your problem. To stop interference you need to make sure everything is earthed very well. It's also important that the antenna's SWR is as low as possible. The T251 would only give you more power and therefor more problems. If you are good with electronics you might try building a Low Pass filter to put between the transmitter and antenna and see if that helps. Good luck!

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  25. Apologies. I forgot to include my name in the last post. I'm Dave.

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  26. Eddy, did you ever put the unit into test mode? Mine got put into test mode accidentally and now I can't get it back. Any suggestions? thanks

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    1. No I never tried the Test mode myself. I didn't want to use it if it wasn't necessary. But it's weird you can't get out of it. I suppose you tried all the obvious things like letting it go through a test and switching on and off. I wouldn't know what else to do except contact the seller for advise.

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