Need help!!!

[sunfireguy]

I got an issue with my external speaker for my scanner.

Heres what I got:

I have a bc246t hooked up to an external mobile antenna, and an amplified external speaker. This all worked fine. The problem I am having now is I installed a cb radio (Yes I know Ham Radio is much better but can't afford it right now, and no license, YET) in to my car, with Barjan 3 foot fibreglass whip. The scanner is wire to the car stereo ignition power (currently no fm radio installed in my car). The external speaker is wired to a cigarette plug, so i can unplug it and move it if need be. My scanner just runs off its batteries.

Now the problem:

The problem I am having is when I key up the Mic on my cb, I get really bad feedback from my external speaker. Everything I say comes through the speaker, and it isn't even hooked up to the cb, its hooked up to the scanner. This being a problem I can't talk on my cb and listen to the scanner cause, the sound of my voice on the external speaker drowns out the sound from the scanner.

Hope you guys can help, cause you guys are all very knowledgable in this stuff.
Thanks

 

[cellblock776]

Wrong forum. This is for photos of shacks and installs.

 

[sunfireguy]

The whole reason I posted on this forum, is because you guys istall your radios, and I was hoping you might be able to help me figure out my install problem!

 

[UPMan]

You need to have better isolation between your CB antenna and the scanner's receive antenna. Having the receiver's antenna in close proximity to any TX antenna will cause massive overload, resulting in anything from temporarily reduced sensitivity during TX to the effects you are seeing to actual damage to the receiver.

You don't mention relative antenna positions, but I'd try one on the trunk and one on the top front.

 

[sunfireguy]

ok, i've done that. But I noticed that even if I don't have the external speaker hooked up to the scanner, it still does it. Could this be a power or grounding issue???

 

[UPMan]

It is probably the strong signal overpowering the scanner's front-end...the scanner is basically receiving the signal on all frequencies and playing it through the speaker. You need better RF isolation.

Check to see if it happens if you disconnect the scanner's antenna, external speaker, and DC cord (I suspect that it won't). Then, connect each external connection one at a time and test...when the interference comes back, you'll know what path the signal is taking to get into the scanner.

 

[sunfireguy]

ok, here's the thing the scanner is not even in the car right now, the cb is grounded and powered through the car radio's wiring, keep in mind that there is no fm/am radio in my car. the external speaker is hooked up to a cigarette lighter plug. Now with only the cb and the external speaker hooked up, and the external speaker is not plugged into anything, just the power, If i key up the mic on the cb, I hear myself. Could this be a bad ground or is it something else. My scanner antenna isn't even hooked up to anything.

 

[UPMan]

Sorry. I thought "even if I don't have the external speaker hooked up to the scanner, it still does it" meant that the audio was then coming from the scanner.

Sounds like you are using an amplified external speaker, and the RF is getting into the amp circuit of the speaker. I wouldn't expect there to be that much RF getting back into the car from an outside antenna (CBs are max 4 Watts RF out). I'd start to suspect a problem with the CB (or really poor AM rejection in the amp circuit of the speaker).

 

[sunfireguy]

So there's really nothing I could do about it then

 

[ve3zo]

So there's really nothing I could do about it then

Isn't RF a wonderful thing. Try wrapping your speaker wire around a torroid. This may help choke some of the RF and stop you from hearing it in your speaker.



Chris
VE3CTP

 

[N9PBD]

Try a shielded cable between the speaker and the scanner, and also make sure you ground your speaker to the car body (metal.)

So there's really nothing I could do about it then

 

[Signal3and2]

You MIGHT try installing a low-pass filter inline between your CB and antenna, preferably closest to the CB as possible. This would eliminate any stray RFI and frequency multiplicative (darned if i can remember the right term for that right now) that may be causing your problem. Basically what is happening is your external speaker is acting like a mini AM receiver without the receiver, but the audio modulation is so strong that it's bleeding over what would be the audio circuite of that "AM receiver". I also like the torroid coil idea that another member threw out.

 

[kc8bdk]

Sunfireguy,

I have a similear issue to yours, there are several CB'ers around here that have *ahem* more than four watts.. beleive it or not.

Every time they key up as driving past my house, they bleed thru the speakers to my computer and my TV in the bedroom.

something in the pre-amp is resinant to the frequency they are transmitting on, picking up the conversation, and passing it to the amp.

You can try to use a torroid... you can try sheilded cables... hell, sheild the entire speaker. it might work.. it might not. experiment... as long as you dont destroy the speaker you will hit on the right combination of "fixes" that might solve your problem.

Some of the speakers even pick up and transmit the "nextel" digital sounds too. I am so blessed my computer does BOTH... not!!

 

[sunfireguy]

Thanks for the ideas. I noticed today while I was screwing around with it, that if I cover the headphone jack on the external speaker, It doesn't do it anymore, but the moment I take my fingers away from the tip of it, and key up the mic, it cause the interference, I also noticed that the closer to the cb antenna wirre I got the louder it got. I don't know, I figured out what was causing it, just have to figure out how to fix it. Also what is a torroid?

 

[Signal3and2]

Sunfireguy,

I have a similear issue to yours, there are several CB'ers around here that have *ahem* more than four watts.. beleive it or not.

Funny thing is, I have *ahem* more than four watts. More like 200 or so, but I don't come through ANYTHING in my own car. It's really wierd. Ive got 4 other radios and 2 external speakers and I can't hear myself through anything. You'll just have to play around to see what works.

 

[N4UYV_Al]

I'm still waiting to see if anyone is gonna ask him what his SWR is on that 3 foot fiberglass whip he's using on his CB radio....