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Re: Advice

KENT BRITAIN
 

Since I gave Sam an handful just a few weeks ago, he should have the 1.5-15's.
And at reduced performance they do work down to 800 MHz.

Wish I had enough power to test them to destruction.
50 watts of SSB or CW should be fine.   FM or one of the near CW digital modes
would be close, sort of depends on the length of your feedline.

BUT, it you cook it, let me know at what power level, and I will get you another one.
Good data point.


From: "'g7jtt@...' g7jtt@... [ukmicrowaves]"
To: "ukmicrowaves@..."
Sent: Sunday, May 13, 2018 11:22 AM
Subject: Re: [ukmicrowaves] Re: Advice

 
Hi Kent thanks for a very informative reply I have one of your log periodic pcb antenna's so will give that a try. I see G4DDK does not stock your 1.5 to 15Ghz Vivaldi antenna, is there any likely hood of this changing ? If not will need to order directly . Also what is the power handling of the antenna's as I have around 50w on 23cm and 13cm whilst only 2w on 3cm.

All best John


On Sun, 13 May 2018 at 15:44, KENT BRITAIN WA5VJB@... [ukmicrowaves]
wrote:
 
Log Periodics do work well as a dish feed.
I agree, not quite as well as an optimized scalar feed, but the difference
is about 1 dB on a small dish.  And you get 3 or 4 ham bands.

The feedpoint of a dish is a theoretical point and usually calculated as though the
dish is used at optical frequencies.    In testing well over 100 dishes, the optimal
position for the feed is almost always closer to the dish than the calculated feed point.
In part this is because the feed is not an infinitesimal point.

Yes, the phase center of a log periodic does move, but it doesn't move very much.
When optimized at the highest frequency of use, the phase error at the lowest
frequency of use is quite minor.

Another option is using a Vivaldi antenna for the feed.  I like to think of a Vivaldi
and a Ridged Horn without the horn.    Phase center is pretty constant with
frequency.   The Vivaldi has about 2 dB more gain than a Log Periodic and would
be more suitable for most offset fed dishes.

73  G8EMY/W5


From: "g7jtt@... [ukmicrowaves]" <ukmicrowaves@...>
To: ukmicrowaves@...
Sent: Sunday, May 13, 2018 7:44 AM
Subject: [ukmicrowaves] Re: Advice

 
just came across this site which has a multi band ring feed http://gvnweb.ddns.net:8081/dish1.html and links to some design software as well. the only thing is this is used on a prime focus dish are these feeds ok to use with an off set dish ?

cheers John 
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