Two Ramsey FM transmitter kits with the same issue?

[cwilliamsws6]

Curious if anyone with more electronics knowledge than myself can offer some insight.

My coworker's dad recently passed and he was a huge radio guy. My coworker didn't know what to do with all of his old radio stuff so he gave it to me. Among it all were two Ramsey FM transmitter kits, already built. One is an FM10 the other is an FM25.

Both of them have practically no signal output whatsoever. I can only pick up the transmitter within a couple inches of its antenna. I tested this with several different radios also. Quite literally the antenna on the receiving radio has to be physically touching the transmitter's to be able to receive anything...

The FM10 is set up for 88.7mhz, the FM25 is set at 102.3.

I removed the little whip antennas that stick out of the top and tried external antennas on both transmitters and made sure they were the appropriate length for the frequency, still having the same issue.

What do I need to look at to get both of these working properly?

Thanks in advance.

 

[meep]

It would be hard to tell without a signal SWR meter to both check the output and tune the antenna properly. A poorly tuned antenna can destroy the transmitter.

ARRL antenna book would be a good place to start (amateur radio relay league!)

 

[supton]

Would have to dig into it. Want to say, very likely low power kits, but should have better range than that. Find the manual and double check the build.

One possibility, its trying to transmit at half frequency and the harmonic is way down. Or more likely, the output filter is tuned way off (was not properly peaked).

 

[chemman]

I found the schematic for the Ramsey FM-10 transmitter and the assembly manual (schematic is at http://www.gbppr.net/lpfm/fm10_schematic.jpg and the assembly manual is at https://www.manualslib.com/manual/521837/Ramsey-Electronics-Fm10a.html?page=3#manual).

The transmitter itself is an integrated circuit. The RF output of the integrated circuit is amplified to around 10 milliwatts by transistor Q1 (a 2SC2498 which can be replaced with an NTE23 transistor). My guess is that either the 0.001 microfarad disc capacitor is not passing the RF to the transistor or the transistor itself might be bad.

As far as the Ramsey FM-25 goes, there are 2 versions, the FM-25A, and the FM-25B. If you determine which version you have, I'll be more than happy to assist you in finding the manual and schematic.

From what I saw, the FM-25? is much more complex than the FM -10 transmitter.

Good Luck!

 

[wag123]

I found the schematic for the Ramsey FM-10 transmitter and the assembly manual (schematic is at http://www.gbppr.net/lpfm/fm10_schematic.jpg and the assembly manual is at https://www.manualslib.com/manual/521837/Ramsey-Electronics-Fm10a.html?page=3#manual).

The transmitter itself is an integrated circuit. The RF output of the integrated circuit is amplified to around 10 milliwatts by transistor Q1 (a 2SC2498 which can be replaced with an NTE23 transistor). My guess is that either the 0.001 microfarad disc capacitor is not passing the RF to the transistor or the transistor itself might be bad.

As far as the Ramsey FM-25 goes, there are 2 versions, the FM-25A, and the FM-25B. If you determine which version you have, I'll be more than happy to assist you in finding the manual and schematic.

From what I saw, the FM-25? is much more complex than the FM -10 transmitter.

Good Luck!

Ceramic disc capacitors generally don't fail. My guess is that the output transistor is bad. One thing that I would do before anything else is to go through the circuit board and re-solder all of the connections (just put the soldering iron on each of the printed circuit pads and re-melt them).
Looking at the schematics, it looks like the 10mw output FM-10 is largely the same concept as the 25mw FM-25 except for programmable PLL frequency control and two transistor output stage (using two of the same 2SC2498 transistors) on the latter.
The 2SC2498 transistors can be purchased for cheap on Amazon or eBay.

https://www.amazon.com/GaueLery-2SC2498-10PCS/dp/B0CNCDYMRX