[50mhz] Yagis

Tue Aug 24 20:33:42 EDT 2010

Bill, ignore some of what I said in the last post as this one of yours just 
came in after I sent it.

It sounds as if we are on the same page.

Carl
KM1H

----- Original Message ----- 
From: "Bill VanAlstyne W5WVO" <w5wvo at cybermesa.net>
To: <50mhz at mailman.qth.net>
Sent: Tuesday, August 24, 2010 8:09 PM
Subject: Re: [50mhz] Yagis

> 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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