[Moon-net] VHF Antenna Noisetemperature by YU1AW..

[Earl (Jim) Shaffer, WB9UWA]

HI All.

I did a quick once over on the paper.
It seems to me that the author wants us to consider comparing antennas at
400K sky temperature on 2M, but I missed the temperature he wanted to use 
for ground.
270K is often used and VE7BQH uses a closer to Urban 1000K.
IMHO, an even higher number than 1000K should be used for Urban ground.
I like to plan for best EME conditions and don't wish to limit myself, so 
sky temp
should probably still be around 200K.
I have found in the past that EME RX is in direct proportion to how noisey 
the
band is. We also know how much SV1BTR increased his RX in a very noisey
location by using a very low sidelobe antenna (my 15 element design).

The trade-off between gain and sidelobes or any other G/T calculation can 
not
be a hard fast calculation. The need changes sometimes from moment to 
moment.
There are times that the lowest possible sidelobe antenna will not tame that 
birdie or line noise
and there are times that only maximum gain designs will can pass the EME 
signal at all.
In the end your choice has a lot to do with your transmitter power. If your 
TX power is
very low, you better maximize your antenna gain. If you have plenty of TX 
power,
consider sacrificing 1/2 db or so to improve your pattern substantially. If 
JT65 is your thing,
then 1/2db of antenna gain is nothing to sacrific for a potential 6db or so 
of RX improvement.

Throwing other factors than gain and noise into figure of merit tries to 
oversimplify an antenna.
The wrong antenna could easily be chosen as a result when for instance very 
low sidelobes
should be the priority.

There is little practical difference between commercial antennas. They are 
pretty much all
maximum gain designs. Your practical choice is to then to chose your boom 
length wisely.
The I0JXX16 stands out as a low temperature commercial design however.

73, Jim Shaffer, WB9UWA.



----- Original Message ----- 
From: "Edward Cole" <kl7uw at acsalaska.net>
To: <moon-net at list-serv.davidv.net>
Sent: Friday, April 18, 2008 9:41 AM
Subject: Re: [Moon-net] VHF Antenna Noisetemperature by YU1AW..


> Only made a quick and partial reading of the paper, but it appears
> the new paper addresses the T portion of the G/T figure of merit used
> in Lionel's study.  This would only result in a across the board
> shift in G/T numbers with the relationship between antennas remaining
> (as Graham says the ranking would would still hold).
>
> For making better estimates of the Lunar path link it may have impact
> since it affects the outcome of total receive noise temperature.  An
> interesting paper that I will read completely as some point.  I have
> spent a great deal of time with NF analysis and path link formula.  I
> wrote a G/T spreadsheet some years ago for the SETI-League for
> antenna measurements using the sun.
>
> In my (early) opinion this paper does not invalidate Lionel's work.
>
> 73, Ed - KL7UW
>
> At 06:57 AM 4/17/2008, graham wrote:
>
>>Bodo,
>>
>>
>> >Does it means that the list of VE7BQH is more or less
>> >an academic paper?
>>
>>It means that YU1AW does not agree with the chosen numbers to construct 
>>the
>>table that BQH made.
>>
>>That does not invalidate the Table or the comparison for that given set of
>>parameters.
>>
>>The BQH numbers where chosen as representative of an 'urban' qth (Tgnd) 
>>and
>>representative of the lowest Tsky.
>>
>>If you look at Page 3 of AW's paper you will see a graphical 
>>representation
>>of 'typical' noise temperatures, here you can see that even greater Tgnd
>>numbers are predicted than those used by the BQH method.
>>
>>If you look at Page 10 you will see that AW proposes an even higher Tsky
>>than that used in the BQH method.(In the new figure of merit proposal by 
>>AW)
>>
>>It seems the purpose if the AW paper is to introduce a more sophisticated
>>way of quantifying and comparing Yagi antennas. Which of itself is fine 
>>and
>>I agree this could be done.
>>
>>Although I have not spent the time to study the AW actual proposal in
>>details (ie running models and numbers here) and what implications it 
>>might
>>have in 'ranking' existing antennas. I would have expected such a paper to
>>contain as a minimum 'several' worked examples ( it contains none at all).
>>
>>I did spend many weeks re_running the BQH Table on models with alternative
>>numbers plugged in the Tsky and Tgnd. It makes very little difference to
>>any 'ranking'.
>>
>>I would suggest then;  that the AW paper is an "acedemic paper" and the 
>>BQH
>>method represents years and years of hard work (helped and verified by
>>many) that offers a practical tool rather than a theoretical proposal.
>>
>>If , after more work, we see the result of the AW proposal really does
>>offer a better tool then I'm all for that.
>>
>>Graham F5VHX, G8MBI
>>
>>
>>
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