Uniden pc78xl receive

[LoneWolf TN]

Howdy howdy. I want to do some rx filtering on my Uniden pc78xl. I want to do some diode changes etc to help with the noisy rx. I need to know exactly how to do this, faster switching diodes, maybe double stacked filters etc. Any help and info would be great.

LoneWolf TN

 

[DX Vader]

I am curious if it is a newer model? My 78 Elite has a very quiet and sensitive receiver.
Perhaps Justin can help you out?

 

[nomadradio]

Hmm. How long until someone suggests "Unplug The Antenna"?

If the noise is originating in your vehicle, there is NO substitute for suppressing the noise at the source. Before it gets launched into the air, and pulled back in by your antenna.

Once that happens, there isn't all that much you can do to the receiver.

Trying "hot-carrier" diodes to replace a few of the stock silicon diodes may make some difference to the receiver. Still won't pull a S-6 station out from under S-9 fuel-pump motor-brush noise, or brush noises from the air-conditioner blower.

If it were that easy, I suspect you would find dozens of "how-to" web pages showing exactly what to do.

Or you could turn off the car's ignition to receive. Makes me suspect that your mobile radio hears a LOT better with the key removed from the ignition lock.

73

 

[LoneWolf TN]

f

DxVader, you're right, the rx is not that noisy. A friend here locally has done the faster switching diode swap and double stack filter mod to several Uniden radios with great success. I couldn't find schematics and block diagrams for the pc78xl so I needed to know if someone has the info on how to do the mods to this radio.
Nomad, you are right on the money - the fuel pump, and you knew it from previous posts... I'm going to try the rf choke installation to the fuel pump wires today and see if that takes care of the unbearable noise coming in through the antenna. I'm always trying to do an easy fix, and most of the time that just don't cut it.
Oh ya, the rx is as quiet as can be with the engine shut off.

Thanks, LoneWolf TN

 

[LoneWolf TN]

f

OK, I quit being lazy today and got under my Ford pickup. I installed two rf chokes a budy of mine had laying around wrapped many times with same ga wire coming from fuel tank. I put one choke on each wire, hot and ground. This seemed to work quite nicely. I'd say it eliminated around 60% of the fuel pump noise. I would have liked the noise reduction to have been more like 90% - I know, picky picky picky...
I still need to do a littly filtering to this radio. Since I can't find any schematics or block diagram on the newer pc78xl, maybe there is another radio board that is layed out like the pc78xl???

LoneWolf TN

 

[cbshack]

I thought the Cobra 29 LTD was a similar chasis. Have you tried looking for a block diagram for that radio?