Dan Zimmerman N3OX wrote:
>On Tue, Feb 17, 2009 at 7:41 PM, Richards <jruing@ameritech.net> wrote:
>
>
>
>>I am not sure what you mean by this... as the Cushcraft MA-160V is only
>>30 to 36 feet tall (adjustable stinger) and only has a 40 kHz bandwidth
>>on 160 meters. The 43 footer is taller, and can be worked anywhere in
>>the band with a big outboard tuner.
>>
>>
>
>
>With miserable efficiency! The MA-160V could easily be substantially
>better, given the coax and balun losses inherent in the 43 foot vertical
>approach, even though, as you point out, the MA-160V is shorter. But top
>loading is a good thing for getting radiation resistance. I don't really
>feel like modeling the radiation resistance of a 43 footer vs. a top loaded
>36 footer... but it might be that the 36 footer wins.
>
>
>
I tend to agree, Dan.
Off the cuff, I would expect a 43 ft radiator with no top loading to
have a radiation resistance of 2 to 3 ohms. This would produce
acceptable results if you have a really good ground, but over a mediocre
ground I suspect the results to be disappointing.
With proper top-loading you could expect to get the radiation resistance
up to something like 6 ohms (perhaps higher if you use the technique
that Rick and Jim recommend ). That's a cheap 3dB when driving against a
mediocre ground. Starting with a mediocre ground and putting lots of
radials down would probably buy another 3dB.
BTW, aren't the top-load verticals in N7JW's 28 element 160 meter array
in the Utah desert only 60ft tall? I know he has transmitting capability
at his house, but I thought he also trasnmitted from the remote site
w/100 watts.
73 Mike, W4EF..........
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