FM25b modification help

[Pastaboy62]

Ok, I bought a pre-assembled FM25b a couple weeks ago. I hooked it up and it works perfectly in the house. Now today I go and try broadcasting outside, and I can not find a good frequency, they are too fuzzy. I tried hooking it up to the dipole antenna I got at Radio Shack, and that still did not work.

I live in a very air wave populated area. There is a major radio antenna behind my house and I live an hour away from NYC so I get all that too.

What do you guys recommend to help me get this to really work.

[Mike Sigmond]

If it helps at all the antenna works best at the same level as the car antennas. You may have a damaged transmitter, hooking up larger or booster antennas can damage the unit as well. It could be that the antenna power level is set too low but I am sure you have checked that.

[seven_siamese_cats]

Ok, I bought a pre-assembled FM25b a couple weeks ago. I hooked it up and it works perfectly in the house. Now today I go and try broadcasting outside, and I can not find a good frequency, they are too fuzzy. I tried hooking it up to the dipole antenna I got at Radio Shack, and that still did not work.

I live in a very air wave populated area. There is a major radio antenna behind my house and I live an hour away from NYC so I get all that too.

What do you guys recommend to help me get this to really work.

What do you mean about the frequencies 'they are too fuzzy'? Are you saying that your transmission is fuzzy outside, or that there are fuzzy signals on the frequencies you are trying to use?

The first thing is to do is find your frequency. Sit outside in your car and go through the whole FM band, making a note of any frequencies which have no signal on them whatsoever, and if there are not any, those frequencies which have a very, very weak signal on them. Look for any sets of 3 frequencies where the center one has no signal (or very, very weak) and the ones on each side have no or weak signal. Set your transmitter to the 'best' frequency you find.

You say that it works well 'indoors', but not outdoors. Is your antenna outdoors? Perhaps the walls of your building are blocking the signal.

[Pastaboy62]

If it helps at all the antenna works best at the same level as the car antennas. You may have a damaged transmitter, hooking up larger or booster antennas can damage the unit as well. It could be that the antenna power level is set too low but I am sure you have checked that.

Why would the manual mention using a larger antenna if it may damage the unit? No I did not check the antenna power level. How do I adjust that?


What do you mean about the frequencies 'they are too fuzzy'? Are you saying that your transmission is fuzzy outside, or that there are fuzzy signals on the frequencies you are trying to use?

By fuzzy I mean the frequencies I am trying to use.

[Mike Sigmond]

Why would the manual mention using a larger antenna if it may damage the unit? No I did not check the antenna power level. How do I adjust that?





I meant hooking up booster antennas or amps. a physical larger antenna should be ok.

It might be a dial on the board if you have that model, maybe someone else knows this model better, I use the FM30.

[Bill V]

I'm just outside of Washington DC and have a fair amount of radio stations to deal with as well. Have you tried using http://www.radio-locator.com/ It has worked well for me.
Good Luck!

[JonB256]

The radio locator website confirmed what I already decided by using my car's FM radio. I just sat in the car and went up and down the dial listening, once during the daytime and once at night.

I picked 95.5 based on listening. When I checked the website a month later, it said that 95.3 was better but that 95.5 was almost as good. I didn't change.

I have a 3/8 wave antenna (E-Bay purchase) hooked to my FM-25B. DON'T DON'T DON'T be tempted to try using a self-powered Radio Shack SWR meter to your radio. It doesn't put out enough power to get a reading and will probably harm the final stage amplifier chip.

Don't use an external antenna and also leave the telescoping whip attached. One or the other, not both. You will harm the final stage chip. Maybe not immediately, but eventually.

There are three readily adjustable potentiometers inside. R28 and R27 are the Left and Right stereo channel input adjustments. It is very easy to set them "too loud" and get distorted sound. Set them "too low" and you get low output volume and too much hiss. These two potentiometers will let you connect to almost any input source cleanly, but they are usually what someone sets "wrong" and gets distorted sound.

R25 is the output gain control. I seem to remember that full clockwise is maximum gain. Try it each way to be sure, but there is rarely a reason not to have it a full gain.

[Pastaboy62]

I have a 3/8 wave antenna (E-Bay purchase) hooked to my FM-25B. DON'T DON'T DON'T be tempted to try using a self-powered Radio Shack SWR meter to your radio. It doesn't put out enough power to get a reading and will probably harm the final stage amplifier chip.

Don't use an external antenna and also leave the telescoping whip attached. One or the other, not both. You will harm the final stage chip. Maybe not immediately, but eventually.

There are three readily adjustable potentiometers inside. R28 and R27 are the Left and Right stereo channel input adjustments. It is very easy to set them "too loud" and get distorted sound. Set them "too low" and you get low output volume and too much hiss. These two potentiometers will let you connect to almost any input source cleanly, but they are usually what someone sets "wrong" and gets distorted sound.

R25 is the output gain control. I seem to remember that full clockwise is maximum gain. Try it each way to be sure, but there is rarely a reason not to have it a full gain.


I adjusted the potentiometers and it is clear as can be.

Thanks