Can you post a clear copy of the circuit?
Someone here may be able to design the correct balum at the pc board. Then you could use 50 or 75 ohm coax to a 75 ohm dipole.
You might try using 300 twin lead from the ant. and ground at the pcb and run it to the center of a 300 ohm dipole as high and clear as possible and aimed at the street. It would be pretty simple and cheap to try.
and yes I know 300 ohm twin lead is for a balanced line
I'm concerned about that feed-through arrangement, where that whip antenna goes through the hole in the metal case? That doesn't look even close to being right to me, I bet you are losing signal there. Since the company wasn't too concerned about giving you the right size whip antenna, they probably weren't too concerned about that feedthrough arrangement, either, and just kinda "eyeballed" it.
My buddy John at work suggested mounting an SO239 connector where that hole is, and connecting the antenna to that. Also he says to make sure you tune those radials to the same 32" length.
Even with the unimpressive silicon, I think you could enhance the signal strength a great deal with only modest improvements to the antenna and the way the signal is getting out of the box.
Your being difficult about not buying a modern one, they're really cheap and people will actually enjoy the music without needing to wonder why the signal is so weak. If you cant bring something to you, go to it! Why not just bring the transmitter closer to the road so that it's within range? Or, once again just get a new one, if your spending all this money on lights and controllers, why not spend the extra $ for something that works?
Actually, I would avoid the balun, coax, and RF connectors completely. You always lose some signal in those, and you need all the signal you got.
This is the best advice so far.
Put the transmitter on the top shelf of a cupboard and connect a piece of hook-up flex to the antenna terminal and stretch it upwards. The longer the antenna the better and the length can be cut to half-wave. The simple addition of a longer antenna is going to have a greater effect than all the other changes.
Does the circuit have an RF amplifier stage after the output of the BA1404 chip?
Does the board connect to the case?
You should be getting at least 200metres (walkmen are not very sensitive).
Connect the antenna directly to the collector of the output transistor.
You really don't have to "trim" the antenna, but a full-wave will be better than half-wave and any of the shorter lengths. But a full-wave is about 3.3 metres, so all the kits I produce use a 170cm antenna, and the problem is solved.
It looks like the kit has attenuated to signal to near zero. The world record (30 years ago) was 300 miles from 300 microwatts. That’s one million miles for 1 watt.
Yes, that's an attenuator, cut that resistor down and it will probably increase the signal.
The case should be grounded (make sure it is, probably on one of those posts, be sure they didn't paint over it) and that would be the shield on the coax, and no - it won't hurt anything.
I think you might also get some improvement in gain if you just drill that antenna hole out a little larger - darn thing just LOOKS too small to me.
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