[NLRS] Fwd: Re: [BC'ers] Anybody have experience with multi-band feeds?

[Dr. Gerald N. Johnson]

-------- Original Message --------
Subject: Re: [BC'ers] Anybody have experience with multi-band feeds?
Date: Fri, 04 Feb 2011 10:26:27 -0600
From: Dr. Gerald N. Johnson <geraldj at weather.net>
Reply-To: geraldj at weather.net
To: badgercontesters at mailman.qth.net

Some applications of the vivaldi fed horn are at:
http://www.dl1btf.de/service/U.Schwarz%20ICUWB2008.pdf and
http://duepublico.uni-duisburg-essen.de/servlets/DerivateServlet/Derivate-14694/Final_Papers/GM0023-F.pdf 

with patterns and gain curves.
Gain tends to hold fairly constant over a large frequency range as does
beamwidth making them look like decent multiband dish feeds. That moves
the complications to the RF transverter switching to the same antenna
coax connector. A spot fraught with loss possibilities.

73, Jerry, K0CQ

On 2/3/2011 10:08 PM, Jon Ogden wrote:
> I spent an entire summer in college (20+ years ago)  one year working in an anechoic chamber doing pattern testing on a Vivaldi antenna.  The thing had bandwidth out the ying-yang.  Was absolutely beautiful.  However, the entire feed structure radiated like a sieve.  To compensate we put absorber material around the feed to minimize the radiation off the feed so we could see what the antenna really looked like.  It helped some but not that much.  I imagine that simply due to the physics of a  wideband PCB horn (which is really what it is) that you'll get some sort of radiation off the open transmission line structure.  Maybe WA5VJB ended up doing the antenna and feed in stripline (ours was just single layer microstrip).  Doing it in stripline would certainly help to contain the feeds on the feed structure.  Makes feeding a little more difficult but it would help stop the radiation off the sides of the antenna.
>
> But let's put it this way:  This is a truly wideband type of antenna design.  It's definitely a wider band design and an Log-Yag.  It's a slick antenna and would probably work well for you provided the feed problem I saw was fixed and it probably has been since that was a long time ago (and hey I believe it was 1987 or 1988 - the Iran-Contra hearings were on then - I remember listening to the in between tests (radios didn't work too well inside the chamber!).
>
> Jon
> NA9D
>
> On Feb 3, 2011, at 6:02 PM, David Palm wrote:
>
>> I have been corresponding a bit with WA5VJB about the use of one of his
>> log-periodic yagis as a multi-band feed for a dish.  (He actually
>> recommends  using one of his newer Vivaldi PCB antennas, which he says
>> should be a bit easier to connect and a bit more efficient in this role.)
>>
>> I realize that this is at best a compromise solution on every band, but it
>> is extremely attractive to me for a rover set-up to be able to use the same
>> dish from, say, 2.4 - 10 GHz.  I was thinking that I'd try to build a loop
>> yagi for 2.4 GHz and try using the multi-band dish on 3.456 MHz and up (if I
>> get the equipment working in time.)  But you get the drift.
>>
>> I've read the article that Paul Wade, W1GHZ wrote about this (
>> www.w1ghz.org/antbook/conf/WA5VJB_LPA_feed.pdf) and the two take-aways from
>> that were that 1) it should work and 2) it seems best to optimize the system
>> for the highest band and then just take your lumps on the rest.
>>
>> I'm wondering if anybody has any experience on this that they could share?
>> I'm interested in having something ready for the August contest and am
>> starting to plan now.  If you have other suggestions for multi-band antennas
>> for the rover, I'd be very interested to hear your suggestions.
>>
>> 73,
>>
>> David  W9HQ
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