ST-7C CZE-7C CZH-7C FM Broadcast Transmitter Review and Spectrum

[@richard7crowley]

Thank you for a real technical review video. Had to wade through half a dozen ridiculous videos to find this one.

[@danielvieira-br]

Sim, eu tenho um igual ST-7C comprei em 2015 e ele ainda opera perfeitamente. O Segredo é fazer manutenções periódicas de 03 em 03 meses, manter limpo o cooler, uma vez por ano trocar a pasta térmica, ter uma refrigeração auxiliar forçada, aterramento, boa fonte estabilizada e uma antena bem aferida, tudo bem limpo, preservado e ajustado dura muitos anos

[@RobertoSilvaOficial]

Eu tenho um de 15 watts, modelo CZE-15A

[@danielvieira-br]

@@RobertoSilvaOficial Olá amigo, que legal, é um PLL muito bom, bem regulado, com antena boa, bem refrigerado e aterrado certinho vai longe o sinal. Forte abraço

[@RobertoSilvaOficial]

@@danielvieira-br Mano, é show! Sou louco por rádio e minha paixão por transmissores FM começou aos 13 anos. Acho da hora! Conecto meu transmissor na minha SmartTV e retransmito a Mix FM para minha cidade. Posso ouvir em quase qualquer lugar. Foda é a Anatel!

[@danielvieira-br]

@@RobertoSilvaOficial Show amigo. RF é uma paixão. Abraço

[@teste10531]

O transmissor ELE-15S causa interferência em emissoras fm com sinal mais fraco (30dB) quando está próximo dele, tipo uns 15 metros de distância com a antena telescópica interna nele? Até agora não vi ninguém no youtube fazer esse tipo de teste, pra saber se é realmente melhor do que o NIORFNIO T15A nesse quesito.

[@EvgeniX.]

btw there is a secret menu settings that you can change on that one to transmit outside of the fm broadcast band!! just hold power while connecting the power lead, the first screen L/H is the TX power selection, next screen is the upper frequency limit (up into the 150mhz on my unit) and next screen is the lower limit (i was able to set as low as 1.5mhz on mine:) just take care not to transmit on that range cause it'll probably only output Wideband FM which will interfere with AM on the airband above, or the military Narrowband FM below. if you have any idea how to modify the unit to TX Narrowband FM I'll be so much thankful!! great video btw..

[@Isalys555]

Awesome! I have a CZE-7C, illegal to use in my country so It ended up in a drawer but once I tested the range with my car (I live in a small city), at about 5-6km the car radio was still able to capture the signal.

[@MasterpieceIndeed]

I like you. Hows your project going?

[@EvgeniX.]

add a properly tuned high gain antenna and I guess u can double that..

[@jamesmatheson4746]

run it on low

[@uploadJ]

An FM Multiplex signal with no modulation only has a modulating signal of 19 kHz, which is then doubled in the receiver to 38 kHz and used to recover the 38 kHz double sideband suppressed carrier signal which is L-R ... the baseband FM signal is your L+R, so a cheap portable non-stereo radio will both Left and Right channels. WIki should have more details ...Bessel functions given modulating signals and their deviation strength determine whether you actually have a 'carrier' present, since FM 'spreads' carrier energy thru its spectrum according to Bessel functions.

[@daleberg3453]

I'm noticing a lot of noise when the carrier is dead. Has a swishy sound. Not sure how to clean it up.

[@kushmobstaz9610]

Hi man, I have this CZE-7C and I'm using it 24/7 and when first got it I already encountered a problem on the audio. It seems when you increase the line in gain it distorts the audio really bad. And thats why i keep the line in gain of the transmitter as low as possible that the audio output on FM is not too low. But even with that setting with a huge amount of low frequency arrives it doesn't handle it well. But I have smaller and much lower power transmitters. That doesn't distort. One broadcast engineer told me the problem is on the PLL on these transmitters because the PLL on these tend to be quite slow. And when a huge amount of low frequency or bass arrives it loses lock and can arise to distortion. Idk if you've notice that on your transmitter. But if you know some kind of modification on these transmitter let me know. If I not I would just buy another good quality transmitter. Btw If you know good transmitters like 10w or 7w also let me know. Thanks!!

[@jazzforever4631]

Well, that is the subject I was writing about on other Spectramam videos. Stereo audio signal from studio or any other source, must be processed before it is used as modulation for FM Stereo Transmitting. BH-1414 and BH-1415 chips used in your and similar transmitters are having 15 kHz low pass filter, and simple (overdeviation) limiter. But also low frequencies are causing the problems to the some types of PLL. And your sound without special processing can never sound as loud as legal FM Stereo broadcasters using some kind of "Optimod" style device.

[@jerrykrinock]

Thank you for the video. But I would like to have seen the 3rd harmonic (if any) also.

[@meatsim65]

Thanks for the video! I have one now and would like to know more about the pre-emphasis modification you mentioned. I'm looking at a datasheet for BH1415F and can see that the pre-emphasis time constant is set by pins 2 and 21 for the R and L channels. And I can also see that the maximum pre-emphasis is 155 microseconds. But how do I determine the correct component value needed to set it to 75 microseconds?

[@meatsim65]

i think i've found it. t=RC. the datasheet gives the resistance as 22.7kohms, so .000075s / 22700 ohms = 3.3e-9 F I need to use a 3300 pF capacitor to achieve 75us pre-emphasis. I do realize the perceived difference will be minimal, but i'd like to see if i can do it.

​@@meatsim65 Can you do a video with this, i would to modificate this.

[@EastAngliaUK]

good to know I have ordered one today from China I also have the 30 watts one in your video but want something smaller to run.

[@migalito1955]

I bought one and was pretty impressed by the attenuation of the harmonics found at multiples of the tx frequency. For inexpensive its a bit pricier than the human hand I saw in the video, so maybe cheap is not the best use of language for the transmitter?

[@deklerk758]

Do you, or did you ever do sound quality testing of transmitters? I have a Ramsey fmb35, which I love, but I've had it for 20+ years and it no longer provides coverage beyond 5 or 10 feet. It sounds better than any other transmitter I've had, including the one in this video. I also purchased an FMuser adjustable 1-watt (FU-X01BK) transmitter. It has better stereo sound quality, in my opinion than the CZE 1-watt/7-watt transmitter, except for its handling of bass. Especially below 85hz. I have to severely reduce the audio level to have full fidelity or completely cut off the bass beneath 85hz to get it as loud as other radio stations on the dial. I never had that problem with my Ramsey transmitter. Oh, how I wish I knew how to fix it. Anyway, I would love to hear back from you with any recommendation for an FM transmitter where sound quality is the priority. Thanks for making these videos. I love them.

[@nelloiorionifm]

Hi friend, can I inject the mpx signal into this transmitter? transmits it in fm?

[@spectra-man]

Yes, you can inject an MPX into this, but I've never tried it personally. You need to break the connection off pin 5 on the BH1415F and then solder your MPX connection on the part leading away from the chip (not back into pin 5). See here: radionecks.co.uk/viewtopic.php?t=1520 Reports are that it doesn't make it a higher quality signal, but will allow you to use better tools and audio processing, so it may sound better, but the RF signal will not be cleaner.

[@allanjaypalomique7609]

dear sir, is this cze-7c... can be set the rf output into fixed 5watts rf output to use and drive in a 30watts rf booster amplifiers sir?

[@Ron-cd1je]

While it is not a big factor one way or the other for a 100MHz product, I don't think it is fair to evaluate a transmitter for spurious emissions with the boards removed from their housing. The housings, if metal, are part of the RF circuitry, in a sense, and can contribute to increasing or reducing spectrum, especially at higher frequencies, like harmonics of the carrier. So, do your testing with housings left on. Also, when measuring transmitter harmonics, you have to be sure that the level going into the first active stage of the spectrum analyzer is low enough that the test instrument is not contributing power to those harmonics. My recollection of this problem when using HP/Agilent or R&S instruments is that you can't trust harmonic measurements when the first active stage input is above about -20 dBm. This is the level after the internal attenuator of the spectrum analyzer, so if you are running, say, 7 watts, 38.5 dBm, then the sum of external plus internal attenuation must be at least 58.5 dB. This will depend on the specs of the spectrum analyzer, of course. It is not difficult to check for this problem by observing the second harmonic and at the same time stepping the analyzer's internal attenuator in 1 dB or even 10 dB steps. If you switch the internal attenuation down by 1 dB and your indicated harmonic level jumps by more than 1 dB, then you have a problem with too much level.

[@spectra-man]

OK, I'll keep that in mind. I think the results will be negligible though.

[@VasilyVishnevskiy]

Hi, Thank you so much for this review. Since you had it dismantled, do you happen to know what size fan is it? I have ordered one and want to put silent fan on it.

[@allanjaypalomique7609]

sir good day to you... i want to ask is this usig an ic qn8006 that is good ic???

[@Isalys555]

20 min ago I tested it to see if it was still functionning after years in a drawer, works fine but each time I broadcasted something my computer mouse went dead, I had to unplug and plug it again, that's weird, it's not a cordless mouse.

[@spectra-man]

Yeah, that has happened to me many times before with the keyboard too. The only solution is to put the antenna as far as possible from the comp. You don't mention what kind of antenna you are using, but if it's one of those that attaches right on the back of the TX like a rubber duck or telescoping antenna, then you need to get an antenna with a coax cable and place it as far away as possible. You will have better performance with an external antenna anyway.

[@Isalys555]

Yeah it's the stock antenna shipped with the transmitter. I'd like to have fun with this transmitter and make a custom antenna in my ceilling but quite pointless as it's illegal (there's a lot of previous lawsuit for pirate radios in France, they really don't like that). I don't really plan to make a "real" pirate radio. I'll be curious to know why mouse/keybard are sensible to this kind of frequency range.

[@Isalys555]

it's a telescopic antenna.

[@spectra-man]

@@Isalys555 At a high enough concentration, the keyboard and mouse are susceptible to any frequencies. AM medium wave radio has the same effect and is 100x lower in frequency. But yeah, be careful. I only test these transmitters and do not use them regularly. They recently strengthened the laws in the US.

[@NielBernPlatch]

Spectraman am planning to buy low power fm broadcast TX, would you please recommend me one? Thanks

[@jberringer1720]

Any suggestions for cleaning up the signal?

[@AlessandroIV3DET]

does they produce something for AIR band too? from 120 to 140 mhz?

[@tonywestvirginia]

Can you run this unit off of a 12 volt car battery? I know it says 12v on the back but, I don;t want to burn mine up. Trying to get rid of a low "Humm" on the signal. Thank's in advance. Tony.

[@spectra-man]

Yes you can. It is OK at 13.8V. You could also try putting a capacitor and ferrite bead on the power supply. It might be coming from the audio source though. Did you hear the sound with no audio input?

[@tonywestvirginia]

Yes and thank you. It was coming from being plugged right to the sound card!

[@SoundSpeeding]

@@spectra-man how high can it handle the voltage??

[@spectra-man]

@@SoundSpeeding About 14V. You may be able to push 15V, but only for a very short time and it may damage the device.

[@alquin08]

hi, is it possible to connect the output of the unit to an FM RF Amplifier lets say i haad seen in ebay an FM RF amplifier with RF input power of 7 Watts then it will amply into 30 watts of FM Transmission? advance thank you on your response

[@spectra-man]

Yes, that will work. Make sure the amplifier has the correct input power though. If it is a little too much power you can use an attenuator or you can reduce the voltage to the transmitter to make less power to drive the amplifier.

[@alquin08]

thank you very much for your reply, highly appreciated, more power to you !!!

[@daleberg3453]

Yes! I put it through a 40 watt NRG KIT RF Amp. The signal was amazing but it attracted the local radio station corporations engineers who paid me a visit. My problem is I can't stand the sound it creates when talking. There is a lot of noise in the background. Plus it says the frequency response says its 30 hz to 15,000 hz, but it sounds more like 50 to 15,000 hz.

[@jazzforever4631]

@@daleberg3453 Strange? Most of the high quality FM Stereo tuners have 30-15000 Hz response. But some transmitters have 50 Hz high pass and 15 000 Hz low pass. Hi pass is used to prevent problems with some PLO, and it helps not to overmodulate transmission with subsonics. Problems with live studio sound comes from overmodulation by extreme dynamic sounds from microphone, especially on sybilants. Audio to FM Stereo Optimod processing is the answer.

[@daleberg3453]

@@jazzforever4631 I use a DBX 166A. If I turn the level down its very swishy sounding. Lots of noise in the background. I used to have an NRG KIT 4 watt transmitter that sounded great. I put it on the dummy load too long and fried it.

[@danielvieira-br]

Olá Spectraman, o amigo está vivo? Mande notícias.

[@davidconsumerofmath]

Has anybody tried swapping out the very noisy fan with a quiet silent fan?

[@-Tris-]

I removed the fan completely and added a bigger heatsink for passive cooling. Works perfect.

[@pierpa_76pierpaolo]

I wanted to have a curiosity. If there is someone near my home who is using one of these ST-7C transmitters, can I modulate it or even better hear what they are saying once I get the frequency right? In short I would like with this instrument to detect my neighbors who are talking very low but are using special equipment. I am brainstorming to find a solution and now I am finalizing a very simple but I hope it will give me a breakthrough in my investigation. That is all for now and then later I can add more things. Thank you very much.

[@letthebiblespeaks7day746]

How far can it goes

[@Legend813a]

Was this a dead key or with 1k tone?

[@Legend813a]

Hurr durrr nothing plugged into inputs... I answered my own question.

[@AlessandroIV3DET]

is it legal to buy this from China or you will have problems on the custom border?

[@spectra-man]

No problems in most situations. Only problems come from FedEx with PCS electronics.

[@Jhonataflp]

the distance of this transmitter cze 7c reaches far

[@spectra-man]

Yes, maybe 5 miles...

[@kinging123456789]

Whats is the ohms reading you get for the antenna?The one I have im getting no reading.The black part of the antenna got hot when I 1st use it.Its not getting hot any more & the range is about 40 meters.

[@spectra-man]

Yeah, if the range is 40m then somethings wrong. This is 7W so it should go farther. I don't know what you mean by ohms reading: it should always be 50 ohm antenna. You need to use an SWR meter and set the transmitter on low mode (I think this makes 1.5W), then you can tune the antenna with the SWR to the lowest reading. Then put the transmitter back to high power mode. It is better if you have a variable 12v supply cause then you can get it down a bit lower. You always want to tune the antenna with the power the lowest, so it doesn't burn the transmitter.

[@richard7crowley]

You cannot measure transmitter or antenna (or coaxial cable) impedance with an ordinary multi-meter. You must use proper RF test gear and measure at appropriate frequencies (~100MHz, etc.) Remember to never power the transmitter without a proper load (antenna). When I tried this transmitter in a rather narrow canyon, I was getting around 2 mile coverage at 7W.

[@jamesmatheson4746]

camera is wavy

[@marcorivera8585]

Gracias amigo

[@alexnartey8867]

Hi please can I discuss this with you

[@SamandAlexHappyBrothers]

Good video !

[@spectra-man]

Thank you!

[@ericguditz4709]

I don’t get it Also, how did I get on the dark side of KZbin?

[@spectra-man]

Hey eric, Hehe what don't you get? The dark side lol You mean the vacant side? IDK. This subject is pretty specific, so maybe that's why.

[@zeljkoadzic1692]

HI pleas can you tell me witch one is better this one 7w pll from this video kzbin.info/www/bejne/sIbcZ5WVZ8yMhdk or this one in presantation video ST-7C