At 02:34 PM 5/28/2007 +0100, you wrote:
At 12:06 pm ((PDT)) Sun May 27, 2007, Jim Dunstan wrote:
[big snip]
A tuned loop (about 3' in diam.) is my favorite receiving antenna when
living at the apartment on the 9th flr. I put mine on the balcony and tune
it remotely with 12 ft of 300 ohm twin lead fed into a Z-match antenna
tuner.
Does this mean there is no capacitor attached to the loop
and all tuning is done by the ATU? So the resistance of the
feeder is included in the loop resonance?
If so, you could get higher Q and hence more output by
tuning at the loop. OTOH, Q is one of those good things
one can have too much of. ;-)
Regards, Len
Hi Len,
You are correct on all counts. The original purpose of the arrangement was to provide a decent antenna for my SWL activity (Sony 7600 receiver) from 5mhz to 15mhz. The tuner sits inside the window looking out on the balcony. The operation is simple .... when it hits resonance the noise level goes up on the receiver .... that's it!! Compared to the whip antenna the performance is a quantum leap improvement, even if I bring the receiver/whip out on the balcony.
I also built transmitting loops for operation at the apartment, using the more traditional tuning/matching arrangements. They work fine .... when I tuned in to SW station (eg 15mhz ... close to 20M) I could NOT detect appreciable difference in performance listening to SW broadcast stations. Of course, this kind of tuning is not compatible with band hopping.
In order for a loop to be an effective SWL antenna it must able to be mounted remotely and provide a reasonable signal level across a very broad range (at least 5-15 mhz or more). In order to provide a reasonable signal across this broad spectrum the antenna either has to be remotely tuned or be broad banded with amplification at the source. My system is the first ... remotely tuned .... with the distance limitation of approximately 15-20 ft. with balance feed line. If you go beyond that distance the capacitance of the feed line starts to limit tuning range. It is also possible to tune such a loop with coax feed line but the distance is even more limited as coax represents greater capacitance.
Jim, VE3CI
