[TowerTalk] Expected VSWR of antenna near the ground

Peter Voelpel dj7ww at t-online.de
Mon Sep 28 19:14:39 EDT 2015 

Its very unlikely that it free-wheels with that R3503 rotator which is made
with a worm drive gear and chain.
But I am not sure what rotator Dennis is using.
Too bad that California is that far away from Germany, otherwise I would go
for some of the Collins parts.
Nice documentation on your page!

Awaiting that big signal via the long path on 40 and 80 this season!

73
Peter



-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Doug
Ronald
Sent: Dienstag, 29. September 2015 00:29
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Expected VSWR of antenna near the ground
Importance: Low

I e-mailed with VE6FI some time ago after searching to see who else may have
one of these antenna systems. He mentioned that they had to add a friction
break at the twin tower base to keep the antenna from free-wheeling in high
winds. USAP assures me they have these world-wide, some experiencing
hurricanes, and haven't received any reports of that happening. 

I have documented the multi-year effort of assembling this antenna/tower
system on W6DSR.com: Projects-->LPDA Antenna. It takes a bit longer when
only one person puts it together. I add on as I make progress.

-W6DSR
P.S. Also on that site are some tube-related parts I am trying to get rid
of. If you have any interest in tubes for your final, take a look...

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Peter
Voelpel
Sent: Monday, September 28, 2015 3:07 PM
To: 'Doug Ronald' <doug at dougronald.com>; towertalk at contesting.com
Subject: Re: [TowerTalk] Expected VSWR of antenna near the ground

VE6FI got one, may be has some suggestions.

Scroll down on his page:

http://www3.telus.net/ve6fi/New%20Antennas.htm

Perhaps Dons, VE6JY is the same model:

http://alfaradio.ca/ve6jy/images/Log1.jpg

73
Peter


-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Doug
Ronald
Sent: Montag, 28. September 2015 23:49
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Expected VSWR of antenna near the ground
Importance: Low

Bingo!

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Peter
Voelpel
Sent: Monday, September 28, 2015 2:47 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Expected VSWR of antenna near the ground

It´s probably a LP1005 

http://antennas.usantennaproducts.com/item/log-periodic-antennas/-lp-1005aa-
25-kw-rotatable-hf-log-periodic-antenna/lp-1005aa

73
Peter

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of K0DAN
Sent: Montag, 28. September 2015 23:09
To: Doug Ronald; towertalk at contesting.com
Subject: Re: [TowerTalk] Expected VSWR of antenna near the ground

Make sure the booms are electrically separate. Each 1/2 element should be
staggered onto the other boom from the previous one. Some LPDA's have issues

with the feedpoint choke, and how the coax is routed. You might want to look

for those articles (such as this: 
http://www.w8ji.com/baluns_on_log_perodic_antennas.htm).

Wow that is one big antenna!

Good luck!

73
dan
k0dan

-----Original Message-----
From: Doug Ronald
Sent: September 28, 2015 14:42
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Expected VSWR of antenna near the ground

Well, okay, I'm convinced, thanks to everyone's advice, that I cannot expect

a VSWR sweep to yield anything meaningful with the antenna on the ground. So

I've done everything I can on the ground to ensure the antenna has been
constructed correctly. I have verified that there is continuity on every
dipole, with the correct phasing to the transmission line. I have verified
that the coaxial transmission line isn't shorted, and has continuity
throughout. Since the antenna is a commercial product, shipped completely
disassembled, I have to assume it will perform when at its design height of
100 feet.

Unfortunately, I'll only get one chance to get it right, since I have to
schedule a crane and helpers, around the constant wind which blows up here
almost incessantly. Judging by the wind forecast, this week is pretty much
out. The antenna is pretty big; 72 foot boom, 105 foot longest rear element,

about 2800 pounds weight, so once I manage to get it up there, its staying
up there. It covers 3 - 30 MHz, although below 4 MHz, the VSWR can rise to
over 2:1. Over the rest of the range the VSWR is < 2:1.

Thanks for all the answers to my question, -W6DSR

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim
Thomson
Sent: Monday, September 28, 2015 9:27 AM
To: towertalk at contesting.com
Subject: [TowerTalk] Expected VSWR of antenna near the ground

Date: Fri, 25 Sep 2015 18:16:17 -0700
From: "Doug Ronald" <doug at dougronald.com>
To: <TowerTalk at contesting.com>
Subject: [TowerTalk] Expected VSWR of antenna near the ground

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

###  What is the make and model of the LPDA ?     Or is it HB ?
What freqs does the LPDA cover ??   Is it   14-30 mhz.... or 10-30 mhz,
or  7-30 mhz ??    How LONG is the boom ?

##  I assume  you mean  low freq end of boom is on the ground, while the
other end of
boom is aprx 3 ft above the lawn ??   That proves nothing.  If far end of 
boom is 3 ft above
ground, all the inboard eles will be LESS than 3 ft above ground.  IE:  0-3 
ft.    Sure,  You could point
it  straight up to the sky, with low freq end of boom aprx 1-3 ft above the
lawn..and also temp guying the boom with non conductive  guy rope..pita.

##  with my 15m yagi  sitting 3 ft above ground on wooden sawhorses, it
resonates way too
low.   Typ 20/17/15/12/10m  yagi will shift a huge amount higher in freq 
when raised up   from
3’...to  20’.

##  If it’s a commercial built LPDA, just install it to its final height on 
tower.   Or at least temp raise
it to  10-15 ft, with boom parallel to ground.  If its still screwed  up,
you may well have a problem with the assy  /  construction process.

Jim   VE7RF



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