[hpsdr] Proposal for Loop Antenna Project

[Tony Langdon]

At 12:21 PM 7/1/2007, Ken Klein wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>
>Gentlemen;
>
>Here is a project proposal that I would like to present to the group 
>for comments and discussion.  I'm hope you won't find it too long or 
>boring.  Thanks to all for the consideration, in advance.

I like the idea of a magnetic loop antenna.  While I've never used 
one, they are said to be an excellent performer, especially where 
height and space are at a premium (for me, height is hard to attain, 
space isn't too bad).

For me, the project does not solve the greatest difficulty - the 
mechanics of the antenna, especially the tuning system and coupling 
the motor mechanically to the tuning cap, so I'm not sure how I would 
implement that.  I had considered a remotely tuned loop in the past 
(manually tuned), but this issue was one of the major sticking 
points, as was sourcing the parts.

Given the tight tolerances, any tuning system would have to be 
automatic.  The tuning could be accomplished in 3 stages:

1.  Open loop using the currently tuned frequency to set the starting point.

2.  Next tuning stage - peaking the receiver noise.  Since the SDR 
has the ability to "see" a fairly wide spectrum (compared to SSB 
bandwidth) at a time, it should be able to see the peak and adjust 
the antenna so the noise peak roughly lines up with the currently 
tuned frequency.

3.  Fine tuning for minimum VSWR.

Small frequency changes could be achieved with an abbreviated 
process.  Small changes (10's of kHz) could easily be done using an 
open loop process, once the tuning characteristics of the antenna 
were known.  The full process would probably only be needed on 
initial startup and band changes.

Just some thoughts.

73 de VK3JED
http://vkradio.com


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