The LPDA does not use a parasitic reflector. Pointing it straight up with
the low frequency element anywhere near ground level will not give an
accurate swept result. The LPDA needs to be raised up into a horizontal
position. The closer to the final height, the better the measuring result.
Paul, W9AC
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Hargrave
Sent: Saturday, September 26, 2015 9:07 AM
To: 'Doug Ronald' <doug@dougronald.com>; TowerTalk@contesting.com
Subject: Re: [TowerTalk] Expected VSWR of antenna near the ground
Doug,
You cannot get reasonable readings with the antenna on the ground.
You can get more ball park readings by standing it on the back end with the
front elements facing skyward.
Suggest you place the back end of the boom on top of a step ladder and guy
the top with nylon rope.
I hope you have some help with the mechanics.
Good luck.
73, Jim - w5ifp@gvtc.com
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf
>> Of Doug Ronald
>> Sent: Friday, September 25, 2015 8:16 PM
>> To: TowerTalk@contesting.com
>> Subject: [TowerTalk] Expected VSWR of antenna near the ground
>> Importance: Low
>>
>> I have assembled my 19 element LPDA with the front 12 elements about
>> 3 feet off the ground and parallel to the ground. The back elements
>> are laying on the ground, but electrically connected in
the
>> usual LPDA way. Today, as a check before I erect it, I swept with
a
>> VNA, the antenna from 1 MHz through
>> 32 MHz. The VSWR is horrible! It has peaks and deep dips at the
low
>> end, and then at 14 MHz or so, rises to over 5:1 and stays there.
>> Now I didn't expect even 2:1 over the range, but I expected the VSWR
>> on the high end to be at least reasonable, because the front shorter
>> elements are off the ground.
>>
>>
>>
>> Anyone care to weigh in with an opinion? I hoping an expert says this
>> is perfectly normal for an antenna just a few feet off the ground. If
>> not, I'm kind 'a stuck as I have checked all the connections with an
>> ohm meter, and they are all okay.
>>
>>
>>
>> Thanks,
>>
>> W6DSR
>>
>> _______________________________________________
>>
>>
>>
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