Signal Cuts In And Out While Driving.

[supernoma]

When listening to pretty much anything with my BCD396T and a Cobra mag-mount antenna (or my trucks stock FM antenna), the signal seems to cut in and out while driving. While stopped I have no problems at all, just while driving.

Any suggestions?

 

[benbenrf]

Is there a pattern to the signal "drop out" you experience or is it random - both in terms of regularity and duration?

Dead spots ... multi-path (reflections) .... poor signal strength, on the one hand, and/or poor connection on the other hand - the 2 most liklely causes.

2 things to try:

Relocate the antenna
Try is relocating your antenna mounting on the vehicle - make a journey and note down those spots/areas where you experience drop out, reposition the antenna and make the same journey again. It's quite possible that as a consequence of the change in ground plane geometry that occurs from re-positioning the antenna you may well exeperience a reduction in drop outs, or indeed an increase, but overall I suspect you're not likely to realise so much of a difference that its going to be worth while.

Poor Connection
The only other possible cause I can think of is a poor antenna/coax or electrical connection. You dont say anything about your BCD396T momentarily dropping out (as in switching off briefly, then switching back on - does the display momentarily go blank?), so if the "drop outs" are irregular and related to movement/vibration, theres a possibility you have a poor/loose coax connection. Continuity test with a digital multi-meter will quickly address that as the cause, if its the cause. Set things up so you can Manipulate/move/shake the coax/antenna around while testing - if theres a poor connection the multi-meter audio should breifly drop out. Do this with and without the Uniden connected - it's possible, if it is a poor connection it could be the coax connector on the actual Uniden.

 

[zz0468]

Reighley fading... and it's possible you're experiencing a combination of effects that benbenrf mentioned. The fading is frequently just there - it's part of the mobile environment, and not a lot can be done about it, other than insure that signal strength stays above the receiver's quieting threshold. In a normally working radio system, the fading is there, but because the signal doesn't fade into the noise, it's just not noticed.

If your receiver is compromised somehow, i.e. a problem with the antenna, then the fading that's always there dips below the receiver threshold, and becomes noticeable.

Other things to think about are, could you be outside the system's designed coverage area? Are you listening to a simulcast cell from outside it's designed boundaries? What sort of terrain are you in? Wide open spaces, or urban? Line of site to the transmitters?

 

[thunderbritches174]

Sounds to me like due to the antenna changing polarization when vehicle in motion your signal is being reduced.

 

[RadioDaze]

Good advice has been given here, and the upshot is this: even if everything in your system checks out A-OK physically, the very nature of radio waves means that you will have variations in the strength of the signal as you move through its field. Waves will multiply for hot spots, and they will cancel for dead spots. If you pull to the side of the road, you may find yourself in a dead spot, a hot spot, or somewhere in between. You can experiment with this by moving (safely) in your car very slowly along. And remember, one wavelength's dead spot may be another wavelength's hot spot.

Don't knock yourself out trying to make it go away.

 

[supernoma]

I'm using 2 different antennas in different spots on the vehicle and the same spot that's dead when I'm moving is fine as soon as I stop.

I just tried today with a BCT15 and got the same results as the 396.

The problem seems to be with analog repeater systems. Not simulcast.

If anybody else from Windsor/Essex reads this it's La Salle Police/Fire and the VE3III and VE3EOW HAM repeaters.

If it was just every once and a while it wouldn't be driving me crazy, but it makes some conversations unreadable while driving.

 

[mrweather]

What is your "Cobra mag-mount"? Scanner antenna? CB antenna?

The VE3III repeater is in a pretty darn good spot on the CBC tower in MacGregor. With the exception of parts of Leamington (due to the Mt. Ruthven shadow) I've never had any problems listening or getting into the III repeater anywhere in Windsor/Essex County. My antenna is an NMO mount 1/2 wave VHF whip and the radio is a Kenwood TK-790 putting out 45 watts.

I've never tried to monitor other repeater systems so I can't comment there.

If it turns out your current mag-mount is a CB antenna replace it with something designed for VHF. While it's true any piece of wire can be an antenna, one that's properly designed for the band you want to listen too will make a huge difference in reception.

 

[supernoma]

The Cobra mag-mount was a CB antenna which I removed the loading coil and tuned the antenna for 145 Mhz.

 

[mrweather]

So the whip is about 19" long? How is it connected to the base now that you've removed the loading coil?

Mobile 1/4 wave antennas tend to give more "picket fencing" of the received signal than gain antennas (1/2 or 5/8 wave).

 

[supernoma]

So the whip is about 19" long? How is it connected to the base now that you've removed the loading coil?

I kept some of the wire and made a direct connection instead of a coil. Total length is exactly 19"

Mobile 1/4 wave antennas tend to give more "picket fencing" of the received signal than gain antennas (1/2 or 5/8 wave).

Using my trucks stock FM antenna doesn't change reception.