[hpsdr] Proposal for Loop Antenna Project

[Philip Covington]

On 7/2/07, Robert M. Ganter HB9DNN <hb9dnn at gmx.net> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Ulrich, hello list,
>
> > I have such a magnetic loop antenna at my QTH (DL1R) in Munich and a
> > 10 m military  ship board whip antenna with an antenna tuner, both
> > operating at 150 Watt.
> > The whip antenna has always outperformed the loop antenna, which only
> > covers a 1:2 freq. range.
> Question here might be: outperformed where, at RX or TX?
> > The loop antenna requires frequent mechanical retuning for 5 to 10
> > KHz, that keeps you always busy .
> This is both a disadvantage and an advantage. Disadvantage because it
> keeps You busy tuning the antenna, *tremendous* advantage, howewer,
> because such an extremely small bandwidth antenna is an excellent
> preselector.
> I agree with Ulrich that magnetic loops are not the best idea for
> transmitting (very low efficiency). For RX SNR is much more important
> and this is where the loop antenna (maybe even with a preamplifier)
> outperforms broadband antennas. Apart from that a small variable air
> capacitor (or maybe relay switched caps?) can be used because no high
> voltages will build up as is the case even with QRP TX power levels. If
> the switched cap solution works this would even solve the "busy
> disadvantage".
>
> For TX I think even a relatively short wire antenna plus antenna tuner
> will do a better job than a loop antenna.
>
> 73 Robert HB9DNN

If you limit it to a RX antenna then the digitally switched capacitor
idea should work well - I'd think a sequence binary weighted capacitor
values and some analog switches would work.  It would make a nice very
selective antenna for use with something like the Mercury.

73 Phil N8VB

 1183381184.0