[hpsdr] Proposal for Loop Antenna Project

Sun Jul 1 20:13:07 PDT 2007

There is also a very nice loop calculator program from
ki6gd available at:

http://www.standpipe.com/w2bri/software.htm

-don

Jason A. Beens wrote:
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Along the topic of loops...
> 
> Take a look at this page. 
> http://www.nd2x.net/ants.html
> 
> I have seen the truck around town, and spoken with the ham before.  Nice
> guy.  Perhaps he would have some ideas about the practical aspects of
> implementing loops.
> 
> Jason
> KB0CDN
> 
> -----Original Message-----
> From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf
> Of Philip Covington
> Sent: Sunday, July 01, 2007 9:16 PM
> To: Tony Langdon
> Cc: Ken Klein; hpsdr at hpsdr.org
> Subject: Re: [hpsdr] Proposal for Loop Antenna Project
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> On 7/1/07, Tony Langdon <vk3jed at gmail.com> wrote:
> 
>>***** High Performance Software Defined Radio Discussion List *****
>>
>>At 10:23 AM 7/2/2007, Ken Klein wrote:
>>
>>>***** High Performance Software Defined Radio Discussion List *****
>>>
>>>
>>>Subject: RE: [hpsdr] Proposal for Loop Antenna Project
>>>
>>>Tony;
>>>
>>>Thanks a million for the comments.  I'm honestly hoping to get lots
> 
> and lots
> 
>>>from the HPSDR folks for this project.
>>
>>It's an idea worth merit.
>>
>>
>>>To address your questions, I think I have found at least a reasonable
>>>starting point for your concerns.  There are several companies that
> 
> have the
> 
>>>shafts, pillow blocks, couplings, and gears that should provide the
>>>mechanical structure.  I just ordered a handful of parts from a
> 
> company
> 
>>>called Stock Drive Products.  The sell small quantities to guys like
> 
> us.
> 
>>OK, would like to see how it goes.  I can worry about shipping
>>concerns later, I have ways of working around issues such as US only
>>delivery. :)  As long as there's a straightforward way of
>>mechanically coupling a motor to the tuning cap that doesn't require
>>one to have too much mechanical experience or a degree in mechanical
>>engineering... Or a shop full of machinery to make the bits fit! :)
>>
>>
>>>So I envision a motor driving a straight shaft coupled to the cap.
> 
> I'll be
> 
>>>using a 22-turn vacuum cap I just bought as well.  The shaft will be
>>>threaded for a couple of inches, so that I can trap a nut to the
> 
> shaft to
> 
>>>hit the limit switches.  I'm also going to use a couple of small
> 
> timing belt
> 
>>>sprockets to drive a 10-turn pot for position information.
>>
>>Suitable caps and options will be another issue as well.  Vacuum caps
>>would be nice, but what's the cost?
>>
>>
>>>To tune, I'm going to deploy the antenna with the mechanicals in
> 
> place and
> 
>>>tune the antenna using a VNA that I built (the Ten-Tec one available
> 
> from
> 
>>>TAPR).  Any antenna analyzer could be used as well as the SDR itself.
> 
> I'm
> 
>>>going to tune the antenna every couple of kHz throughout the range of
> 
> each
> 
>>>band covered by the antenna and note the position sensor voltage at
> 
> each
> 
>>>point.  From that I'll make a lookup table that will have all these
> 
> points
> 
>>>in code.  Each time the DDS frequency is changed; the servomotor will
> 
> find
> 
>>>the closest resonant point from the table and run the motor to that
>>>position.  This is how I'm going to tune the antenna.  I won't be
> 
> looking
> 
>>How likely is drift with changes in temperature, ageing of the cap,
>>mechanical movement with wear and tear from the wind, etc?  Given
>>that the loop is a very high Q antenna, I would feel more comfortable
>>if the system was able to recalibrate itself (i.e. closed loop)
>>rather than rely on open loop control via a lookup table.
>>
>>
>>>for receiver noise or SWR; I'll just be retuning the cap to the
> 
> previously
> 
>>>determined resonant point for that frequency.  Of course, frequencies
>>
>>How repeatable is this after years of service?
>>
>>
>>>I hope I've explained this well enough.  Let me know if this answers
> 
> your
> 
>>>concerns or if you want more detailed info.  I'm really just starting
> 
> this,
> 
>>>so it might be awhile before I have worked out all the nitty-gritty.
>>
>>Well, the mechanics, I'll see what you come up with.  Electically, I
>>have concerns about your method, because there is no onging feedback
>>to compensate for changes in antenna characteristics due to
>>environmental considerations.  Open loop adjustment is fine for a QSY
>>in the same band on the same day, but may not suffice when going
>>between summer and winter, or if the last hurricane turned your
>>antenna into something looking more like a pretzel! :-D
>>
>>73 de VK3JED
>>http://vkradio.com
>>
> 
> 
> Ken's project can be used for loops and remotely (mechanically) tuned
> antenna tuners, etc...   I don't think he is proposing a mechanical
> design for the loop capacitor driver... though it will be interesting
> to see how he does the mechanical part.
> 
> 73 Phil N8VB
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