[NLRS] Give away + Need advice on DirecTV dishes

[Dr. Gerald N. Johnson]

I've done some more reading, thinking one problem with the Vivaldi is 
that the phase center is going to change with frequency throwing it out 
of focus.

Some say that is absolutely true, some say not. Some say the Vivaldi can 
be designed for a clean pattern with at least 10 dBi broadband gain, 
some average 6 dBi and peak at 8 dBi. From my reading I concluded that 
for every one who seriously designs a Vivaldi (and there are major 
variations with different aperture tapers, linear, circular, and others 
described only by their creator's name) there are at least a dozen 
different designs with different characteristic.

www.cresis.ku.edu/sites/default/files/TechRpt135.pdf seems to put the 
design emphasis on compactness much smaller than most designs but 
includes a considerable survey of the literature and discussion of 
design tradeoffs.

www.ieee.cz/mtt/soutez07/Nevrly.pdf put emphasis on broad band with a 
frequency insensitive phase center so the UWB transmitted and received 
pulse is not broadened unreasonably. So their antenna and feeds were 
experimentally (much with analytical software) optimized for a 
compromise on impedance match giving priority to pulse quality.

It is possible to design for higher and lower gains depending primarily 
on the aperture height and the length of the taper which is exponential 
if its a true Vivaldi. But Neverly shows at least 8 different 
exponential curves and their effect on pulse quality and impedance match.

It begins to boil down to simply assemble Vivaldi and dish and have Kent 
test it on multiple bands at CSVHF in 7 weeks or Donn in a week, perhaps 
build it with the capability of easily optimizing the feed to see how 
much that particular Vivaldi changes with frequency so a compromise 
position (if compromise is needed) to favor the band most in need of 
gain. I think it will show gain, but a bit off what the DirectTV dish 
would do with the optimum feed on all your bands of interest. Then the 
question is having one antenna with less gain better than hauling 4 or 
more, can enough of the gain imperfection be made up by site location, 
antenna elevation above ground, TX power, and receiver preamp?

73, Jerry, K0CQ

On 6/7/2013 8:55 AM, David Palm wrote:
>
>
> Jerry wrote:
>
> The Vivaldi that Kent sells is 10-25 GHz, not very useful on 3.4 GHz. His
> PCboard log periodic that does cover 2.1 to 11 GHz has less gain and I
> think the spill over the sides of the dish will be great, hurting the
> transmit gain and the receive signal to noise ratio.
>
> The Vivaldi that I got from Kent is 5 - 18 GHz, but he says it works down
> to 3.5 GHz.  It's quite a bit bigger than the 10 - 25 GHZ model.
>
> So Jerry, I wonder if you can clarify: are you saying that the Vivaldi will
> do a better job at limiting overspill than the log periodic?  Or are they
> both equally bad in that regard?
>
> Donn wrote:
>
> I look forward to seeing the multi-band dish on the antenna range.
>   (Assuming the WX is such that we can do another antenna range.  We got
> skunked at Aurora last month and next week's make up is iffy with the WX
> pattern we seem to be in.  Maybe later in the summer....
>
> Thanks for your encouragement, Donn.  Yes, if the antenna range is offered
> later in the summer I'm going to try hard to get up there for that.  The
> earlier dates have not worked for me, but I'd love to have another crack at
> it.
>
> 73,
>
> David  W9HQ
>
>
>
> On Fri, Jun 7, 2013 at 12:23 AM, Dr. Gerald N. Johnson
> <geraldj at netins.net>wrote:
>
>> The Vivaldi that Kent sells is 10-25 GHz, not very useful on 3.4 GHz. His
>> PCboard log periodic that does cover 2.1 to 11 GHz has less gain and I
>> think the spill over the sides of the dish will be great, hurting the
>> transmit gain and the receive signal to noise ratio. The dish will
>> concentrate the received signal on the feed, but the feed will see noise
>> sources like hot earth from the spillage.
>>
>> You could make a Vivaldi for a lower frequency range, just make it 3 times
>> the size of his 10-25 GHz and it has better gain than the LP, but still may
>> spray RF past the edges of the dish and pick up some noise sidelobes. It is
>> possible to array Vivaldi's but it gets messy.
>>
>> 73, Jerry, K0CQ
>>
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