[50mhz] Cushcraft A50-3S Question

[Curt Sanders]

I've had one of these for years... it sounds more like a bad cable.  
I've found the manual measurements to be reasonably accurate. My  
antenna is only 20 feet up, 10' from my house and surrounded by a host  
of trees and still getting a good SWR reading all around.
Curt, K3URT

On Feb 11, 2008, at 9:36 PM, Bill W5WVO wrote:

> This is a "me too" post.  :-)  Yes, what Jonesy said.
>
> If at all possible, get or borrow an MFJ-259B (or newer) antenna  
> analyzer. This will allow you to adjust the antenna for true  
> resonance (reactance = 0, resistance = 50) at your desired  
> frequency. There just ain't any easy to do that without such an  
> instrument.
>
> Connect it as close to the antenna coax connector as possible -- a  
> one-foot jumper is good. Make your trial adjustment to the antenna,  
> then STEP BACK away from the antenna until the readings stop  
> changing, then note the readings. Repeat. If you have the antenna  
> mounted on a plastic or wooden chair or ladder (NO metal) and  
> pointing straight up at the sky, you shouldn't have to step back too  
> far to get out of the field.
>
> You will probably need to manipulate three things: the driven  
> element length (with exactly equal adjustments on each side of  
> center), the gamma match tap point on the driven element, and the  
> gamma match capacitance (concentric rod/tube overlap). Do NOT adjust  
> the length or position of either the reflector or the director.
>
> If you have never done this before, take your time, and you'll have  
> a LOT OF FUN!!  :-)
> Bill W5WVO
>
>
> Marvin L. Jones wrote:
>> On Mon, 11 Feb 2008, George McCrary wrote:
>>
>>> I'm getting ready to put a used (good condition) A50-3S up at about
>>> 57 feet. I currently have the antenna on an 8 foot mast leaning
>>> against a pine tree.
>>>
>>> I've set the antenna up for resonance at 50.0 MHz according the
>>> measurements in the manual. When I measure the VSWR I actually get a
>>> dip at around 50.8 MHZ where the VSWR is about 1:1. The VSWR at 50.0
>>> is almost 3:1.
>>>
>>> Are the measurements in the manual that unreliable, or is the
>>> antenna being affected by it's proximity to the tree and ground?
>>
>> Maybe.  Probably.  No doubt.
>>
>> Using a tall wooden or fiberglass step-ladder -- full clear of any
>> nearby structures, clamp the mast to the top platform with the  
>> antenna
>> pointing STRAIGHT UP.
>>
>> Now (re)do your SWR measurements -- and insure that _you_ are nowhere
>> inside the antenna's capture area.
>>
>> Jonesy
>
> Moderator: Ray Brown, KB0STN
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