RadioBanter - View Single Post

May 7th 06, 04:23 AM posted to rec.radio.shortwave

In article .com,
wrote:

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 !!!

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 signal.

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.

Yes, either it's an image or the radio front end is just overloaded
because if the BALUN is working right you will have stronger signals at
the radio input. If the radio has a sensitivity switch moving it to
local will do the same thing as removing the BALUN or just using the
whip on the radio.

--
Telamon
Ventura, California