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

[Marciniak, Ed]

I think it would good to get a feel for the pattern symmetry with Vivaldi not using a balanced feed. It could be that the gain could be improved a little with a better feed

----- Original Message -----
From: Dr. Gerald N. Johnson [mailto:geraldj at weather.net]
Sent: Wednesday, March 16, 2011 12:44 PM
To: badgercontesters at mailman.qth.net <badgercontesters at mailman.qth.net>; NLRS Reflector <NLRS at mailman.qth.net>
Subject: Re: [NLRS] [BC'ers] Fwd: Re: Anybody have experience with	multi-band feeds?





On 3/16/2011 9:03 AM, David Palm wrote:
> Thanks for all the great feedback so far.
>
>>> Its a trade off situation, where having individual band antennas can
> speed band changing, but makes on site erection slower. Where the gang
> of loopers make give better performance at the cost of greater antenna space
> volume and more difficult aiming.<<
>
> Exactly.  To me the potential advantage with the multi-band dish is that it
> gets peaked up on a station and then you run some bands with them without
> having to horse around with aiming another antenna.  So if the different
> between a looper on 2304 and the less-than-optimum dish really was only 4-5
> dB, then it might be worth it just to stick with the dish.  On the other
> hand, if I already have a mast with yagis for 902, 1296, etc. peaked on the
> station then having another looper on there for 2304 would be optimal.
>
>>> I think there's been something written recently about feeding a dish with
> the Vivaldi, I'll look for it after while, likely a recent magazine or MUD
> proceedings. I have the feeling that the Vivaldi as supplied by Kent is more
> appropriate for a short focal length prime focus dish than the Direct TV
> style offset dish. Because the pattern of the Vivaldi is more like a dipole
> than a multiple wavelength horn.<<

http://www.mvus.org/apnews/mvus808.pdf reports some success with a 
vivaldi feed. Also results across the lake with the bare feed.

My search showed up reports of Kent testing 11 and 16" dishes with 
Vivaldi feeds at MUD and CSVHF in 2007-2009. I found no information on 
those dishes, particularly their F/D. Kent probably knows more but so 
far isn't talking.

There are single and array patterns in the thesis at:
http://www.ittc.ku.edu/research/thesis/documents/ravi_prakash_rajaraman_thesis.pdf 
looks like the pattern is wider at lower frequencies and a bit wider 
than the F/D 0.7 of the Direct TV dish. The patterns aren't terribly 
clean at any frequency.
>
> I would be interested in seeing this, if you can find it.  It seems that
> basically this is something that just needs to be tried.  Hopefully we can
> give it a go at Aurora '11.  I have both the Vivaldi and the log periodic
> PCB antennas.  It might be interesting to try both, if there's enough range
> time available.

Paul Wade has a chapter in his on line antenna handbook on those LP 
feeds for dishes.
>
> Does anybody have some ideas about the best way to mount a PCB feed?  I have
> some ideas, but I'm not very mechanically creative--it seems that as soon as
> I put something together I'll see an idea that's way more clever than what I
> came up with myself.

If it holds the feed in the right place, with axial adjustment for 
finding the phase center of the feed, and doesn't break its adequate. 
1x2 wood strips are forgiving and more than adequately rigid. One of the 
beauties of the offset fed dish is that the feed support is out of the 
radiation pattern so its not so necessary to make a feed support small 
to prevent antenna blockage.
>
> Finally, I'm probably going to do this with the DirecTV dishes, since that's
> what I have.  But if anybody knows of a place to get a dish that may be more
> optimal for this experiment, I'm certainly open to that.
>
> Thanks and 73,
>
> David  W9HQ
> ______________________________________________________________
>
73, Jerry, K0CQ
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