Thread: balun and image
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Old May 7th 06, 12:57 AM posted to
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Default balun and image

You would have to do some math to show you have an image. That is, an
image is very predictable if you know the IFs used in the radio.

Maybe your front end is overloaded, and going to the whip provides less

Generally if your radio input is a whip, the radio has a huge amount of
gain at the input to make up for the weak signal provided by the short
whip. Some radios have a switch that you set for either a whip, long
wire, or 50 ohm feed, adjusting impedance and gain accordingly.

Charly wrote:
Dear all,

I just noticed tonight that, while listening what seemed to be Bucurest radio on
5900 kHz between 2100 and 2200 UTC, I had a strong image of Vatican Radio. This
Vatican radio transmition was on 5885 kHz, much stronger (closer, I'm in Paris
surburbs, France) than Bucarest. I disconnected my external antenna with balun,
and Vatican radio image disapeared from 5900 freq just listening off the whip.
Then I tried the antenna without the balun : the signal improvement is less than
with the balun, but at least I don't have the image...

The balun is home made, with a ferrite core than comes in two clippable parts
(used to reduce noise on wires) : so it is not a perfect balun for sure, but it
gives good results anyway for me...

I had the same thing occuring with my Sangean 909 and Sony SW100.

Can anyone explain that image phenomena to the humble radio beginner that I am ? :-)

Thanks in advance !!!