Wall-wart VHF groundplanes

[nanZor]

Got a desktop scanner that basically sits on a desk and doesn't use anything other than a rubber duck or other simple spike?

If you power it with a wall-wart, you can make up the missing groundplane for VHF by choking the power lead.

A two-pack of RS #273-104 are ideal for this. Choke it at the output of the wall-wart. Then on your favorite band, choke the power lead a 1/4 wave (234/f mHz) from the end of the connector. I usually cut it about 2 inches shorter since the handheld has a small amount of groundplane internally.

So for my activities centered on 127 mhz, I just choke it at about 20 inches from the end of the connector. The spec-sheet included with the 273-104 make it easy to figure out the wind.

If you have enough of a lead, you can experiment by laying the power lead down horizontally, or just leave it hanging down from the back of the desk vertically.

Obviously this is just a little quickie type project, but is a win-win as you clean up the noise from the wall wart and put the power lead to better use.

With an external antenna, I wouldn't try to choke the power lead at the 1/4 wave point - just at both ends of the power lead.

 

[nanZor]

On a similar note, I do the same thing with my temporary mobile setups with handhelds that have an audio cable coming from the speaker output going to the aux-input of my stereo.

I choke the audio cable as well either at both ends, or at the 1/4 wave point and at the input to the aux connector. It isn't perfect, but it helps!

 

[N_Jay]

How much does it help?

 

[nanZor]

For anything below UHF, quite a bit. (The grounded counterpoise of the internal circuit boards seems long enough on UHF not to really justify it at that band - although there is nothing to stop anyone from trying.)

The main benefit came when I'm operating the handheld with only a rubber-duck, and choking either the power cord or the audio cord at a 1/4 wavelength away from the scanner input on my favorite band.

When I run mobile this way, I have *both* the power and audio cables choked and serving as makeshift counterpoises -- although two wires don't make a great counterpoise, especially when just strung out randomly on the desk or in the mobile.

What I can say is that where I never used to be able to hear some robotic ATIS aircraft broadcasts in my area when mobile, with the addition of just the choked audio cable helping me out just laying randomly on the car floor, I can do so reliably. Other weak signals are now audible, like aircraft towers but I can pick them up further away as I mobile down the road.

However this is all too subjective - it's one of those things you just try and see if it is even worth the effort. And I'm only concentrating on scanning one band.