[50mhz] Yagis

Tue Aug 24 20:09:58 EDT 2010

To amplify on this somewhat -- When I wrote that paper, my understanding of 
antenna dynamics was not as complete as it could have been. Now that I 
understand stuff a little better, I should probably revise the stated gain 
figures to show gain in free space only, so people can do apples-to-apples 
comparisons.

Additionally, even truly flat terrain isn't REALLY flat on 50 MHz if there 
are any buildings around, which look pretty big at that wavelength, so using 
a flat-terrain ground gain model isn't very useful anyway. More useful is 
the terrain-mapped plots generated by HFTA; I later did this for my QTH. But 
even this breaks down somewhat once you get above 50 MHz, because the 
buildings and other structures, which aren't included in HFTA's MicroDEM 
terrain model, will distort the ground-gain pattern unless your antenna is 
quite high -- at which point it will approach the theoretical pattern 
generated by the flat model, if your terrain is actually flat.

Bill W5WVO

--------------------------------------------------
From: "Bill VanAlstyne W5WVO" <w5wvo at cybermesa.net>
Sent: Tuesday, August 24, 2010 23:49
To: "Carl" <km1h at jeremy.mv.com>; <50mhz at mailman.qth.net>
Subject: Re: [50mhz] Yagis

> Joe?? Are you talking to me, Bill, W5WVO?
>
> The gain figures, as stated in the paper, were calculated by YO to include
> estimated ground gain (assuming flat terrain, which I have at my QTH) at 
> the
> specified height above ground (32 feet in my case). YO will calculate gain
> either in free space (what you're talking about) or will optionally model 
> in
> flat-terrain ground gain for a user-specified HAAT and main lobe elevation
> angle, which is 5 degrees by default. At 32 feet, main lobe elevation is
> actually a little higher than that. That's in version 7.58 -- don't know 
> if
> your older version had that capability. It's the "H" command in 7.58.
>
> Bill W5WVO
>
> --------------------------------------------------
> From: "Carl" <km1h at jeremy.mv.com>
> Sent: Tuesday, August 24, 2010 13:46
> To: "Bill VanAlstyne W5WVO" <w5wvo at cybermesa.net>; <50mhz at mailman.qth.net>
> Subject: Re: [50mhz] Yagis
>
>> Joe, how did you arrive at those gain figures? You claim 13.67 dBi for 
>> the
>> stock A50-5S while CC states 10.5 dBi and my own YO 6.5 analysis in the
>> 90's
>> comes up with 9.87 dBi.  I used 50.135 MHz and CC didnt state a frequency
>> which can account for the small difference as they probably quoted peak
>> gain
>> at some frequency above 50.5 which is where I stopped plotting. You and I
>> agree very closely on the F/B and feed impedance.
>>
>> Your extended plot and element arrangement agrees very close with a
>> similar
>> extension I did, also in the 90's, with a resultant 11.3 dBi at 50.135.
>>
>> Tweaking the stock antenna on the same boom length I arrived at a
>> miniscule
>> gain increase to 10 dBi but improved the total F/R to 28.5dB which was my
>> goal. It seems that a roughly 1.4 dB increase by extending the boom buys
>> very little gain unless used in a stack.
>>
>> Carl
>> KM1H
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Bill VanAlstyne W5WVO" <w5wvo at cybermesa.net>
>> To: "Mark D. Tetrault" <mdtetrault at gmail.com>; <50mhz at mailman.qth.net>
>> Sent: Monday, August 23, 2010 9:34 PM
>> Subject: Re: [50mhz] Yagis
>>
>>
>>> Mark,
>>>
>>> If cost is a significant factor in your decision, you might consider
>>> modifying your A50-5S yagi according to my design. It will cost you 
>>> about
>>> $20 max. It has been done by scores of amateurs with good success. The
>>> computer-modeled design will give you a yagi very similar in appearance
>>> and
>>> performance to the M2 6M5X. All you have to buy or otherwise procure is 
>>> a
>>> 6-ft length of 1-1/2" x 0.058" wall aluminum tubing to extend the boom
>>> and
>>> a
>>> couple of hose clamps. Everything else is just changing design 
>>> dimensions
>>> and readjusting the gamma match.
>>>
>>> You can find the paper here:
>>>
>>>   http://www.joeunkit.co.kr/upload/upload251/A50-5S_w5wvo.pdf
>>>
>>> I don't know who this Korean site is, or how my paper got on it, but...
>>> there it is. :-)
>>>
>>> Bill W5WVO
>>>
>>> --------------------------------------------------
>>> From: "Mark D. Tetrault" <mdtetrault at gmail.com>
>>> Sent: Monday, August 23, 2010 22:18
>>> To: <50mhz at mailman.qth.net>
>>> Subject: [50mhz] Yagis
>>>
>>>> OK I'm having mind fart.
>>>>
>>>> I've used Cushcraft's 5 element yagi for years with good results. I
>>>> have now moved to AZ and will be putting up a 35' tower. My CCraft 5
>>>> el is getting old so time to eihter replace it with a new one, or buy
>>>> something else.
>>>>
>>>> Trouble is I cannot remember all the yagis that are recommended. I
>>>> know M2 builds a good one. Who else should I consider?
>>>>
>>>> Tnx,
>>>> Mark
>>>> AA1OV
>>>>
>>>>
>>>>
>>>> Di-Mar Imaging & Design
>>>> Quality Campground Maps & Brochures
>>>> Concord, NH
>>>> (603) 387-9392
>>>> www.di-mar.com
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>>>
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>>
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>
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