Reduce interference from APRS radio

[N0BDW]

Hi all,

I have a Yaesu FT-8800 as my primary rig in my car. It is hooked up to a Comet CSB-790A antenna that is mag mounted to the trunk. I also have a Byonics Micro-Trak RTG that uses a Micro-Trak VHF Antenna V3 antenna. The problem I'm having is that I'm hearing the APRS beacon come through the speaker for the main rig. I'm fairly new to the hobby, but I'm thinking this is either a problem with the antennas being less than 1 full wavelength apart or the speaker is picking up the RF from the APRS transmitter.
So, what can I do to reduce the likely-hood of this problem? I thought about getting a duplexer (not a diplexer - any recommendations?) so I could run both transmitters off the one antenna... and/or installing a ferrite core on the speaker wire...

You can see my setup in this thread:
http://forums.radioreference.com/pi.../197055-mobile-install-2006-chevy-malibu.html

Thanks for any suggestions.

Ben N0BDW

 

[kb0nly]

Since your using the RTG at 10w i would put a ferrite on the speaker wires close to the speaker, see if that helps, very good chance the speaker itself is picking it up.

Using a diplexer wouldn't help in this situation since you have the 8800 dual band radio which is also using the VHF side of the main antenna.

APRS is a bit of a give and take when you have another 2m radio in the same vehicle, its usually a matter of noise and desense when its transmitting and not much you can do about it. It looks like you got pretty good antenna seperation, the one on the trunk is the 8800 and the one on the roof is the tracker right?

I would try adding some filtering to the speaker and see if that helps. The Yaesu/Vertex speaker that your using is pretty easy to take apart, could desolder the wires from the speaker and wrap them through a torroid inside the case then solder back to speaker. The long speaker wire to the radio is probably picking up the RF. I had that problem at one time also.

I run 25w on APRS to reach out around here, after some proper RF proofing i don't have any troubles other than a bit of desense to the other radio if i happen to be on 2m at the same time.

 

[N0BDW]

Since your using the RTG at 10w i would put a ferrite on the speaker wires close to the speaker, see if that helps, very good chance the speaker itself is picking it up.

Using a diplexer wouldn't help in this situation since you have the 8800 dual band radio which is also using the VHF side of the main antenna.

APRS is a bit of a give and take when you have another 2m radio in the same vehicle, its usually a matter of noise and desense when its transmitting and not much you can do about it. It looks like you got pretty good antenna seperation, the one on the trunk is the 8800 and the one on the roof is the tracker right?

I would try adding some filtering to the speaker and see if that helps. The Yaesu/Vertex speaker that your using is pretty easy to take apart, could desolder the wires from the speaker and wrap them through a torroid inside the case then solder back to speaker. The long speaker wire to the radio is probably picking up the RF. I had that problem at one time also.

I run 25w on APRS to reach out around here, after some proper RF proofing i don't have any troubles other than a bit of desense to the other radio if i happen to be on 2m at the same time.

Awesome, thanks for the insight. I will try adding some RF shielding to the speaker.

 

[LtDoc]

Amazing how handy a five gallon bucket of torroids can be, ain't it?

 

[N0BDW]

Amazing how handy a five gallon bucket of torroids can be, ain't it?

I don't even know what a torroid is :-x

I was thinking about something like this:
Parts Express Ferrite Core 1/4" Cord Noise Suppressor

 

[LtDoc]

That's a "torroid", or what's commonly called one.
- 'Doc

 

[N0BDW]

That's a "torroid", or what's commonly called one.
- 'Doc

I see. Well, perfect then. I happen to have a spare one. It may not be for wire as small as what runs to the speaker though, but they are pretty cheap in either case.

 

[LtDoc]

FWIW
Just one ferrite torroid/core/bead/'donut' seldom does much good. Depending on the amount of 'RF stuff' involved, a number of them, and/or a number of windings on each one will increase their effectiveness. There are various 'mixes' of that ferrite that can determine what frequency ranges that can be affected the most. 'Amedon'(sp) used to have references about that sort of thing on their web site, probably still do if you can find it. It can get quite complicated...
- 'Doc

 

[kb0nly]

I see. Well, perfect then. I happen to have a spare one. It may not be for wire as small as what runs to the speaker though, but they are pretty cheap in either case.

Thats actually perfect size wise, try to get as many wraps through it as you can, just flip it open, wrap the speaker wire around that half as many times as you can while still being able to snap it closed, then snap it shut and your done.

 

[N0BDW]

Thats actually perfect size wise, try to get as many wraps through it as you can, just flip it open, wrap the speaker wire around that half as many times as you can while still being able to snap it closed, then snap it shut and your done.

I did as you suggested but am still able to hear the APRS beacon through the FT-8800. I'm almost positive it is coming through the antenna/radio and not just being picked up by the speaker because when it happens the signal level on the 2M side of the radio spikes. Any suggestions on how to deal with that?