[Hi-zreceivingarraydiscussions] Grounds for 4 square

[John Kaufmann]

Paul (K5ESW) and all,

To do my impedance measurements on the verticals, I disconnected the
feedpoint amplifier and connected the antenna and ground leads directly to
the AIM-4170 input port.  At 1.8 MHz, the radiation resistance of a short
vertical is essentially zero, so all the resistance that is measured is
assumed to be ground resistance.  

I measured two of the verticals in my 8 circle and got very similar results.
At that point I didn't bother measuring the rest of the verticals because I
assumed the results would also be similar.  

W3LPL uses passive (non-amplified) receiving verticals.  In his
multi-transmitter operations, the extremely strong RF from the transmitters
would cause serious blockage or intermods in any active electronics at the
array when another receiver is trying to listen through them.   That's why
he uses the passive approach but it also means his verticals are very
narrowband because they have to be resonated (with inductance).  I'm not
sure what kind of combiner he is using and I don't know exactly how he is
doing his TDR measurements.  However, I am guessing he is checking for
feedline discontinuities or faults that would produce reflections back to
the TDR.  The TDR would help him pinpoint the location of the faults.

With the Hi-Z system, which uses active electronics, I'm not sure what you
could learn about the verticals from a TDR in the shack.

73, John W1FV

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Date: Mon, 12 Dec 2016 22:12:24 -0500
From: Paul Ferguson <Paul at PaulFerguson.us>
To: Hi-zreceivingarraydiscussions at hizantennas.com
Subject: Re: [Hi-zreceivingarraydiscussions] Grounds for 4 square
Message-ID: <c317f6d5-12b4-bcbf-81b9-c98883bac7f2 at PaulFerguson.us>
Content-Type: text/plain; charset=utf-8; format=flowed

John,

I also have an AIM 4170C and am interesting in looking at my HI-Z verticals
ground resistances. Did you do the measurement by taking the analyzer to
each vertical and connecting it to the ground rod wire and vertical wire
with the vertical amplifier removed?

I also noted Frank, W3LPL, uses a TDR to check his verticals from his shack.
I assume you cannot get useful information about the HI-Z verticals from the
shack because of the vertical amplifiers, phasing controller, and preamp
being part of the system near the arrays. Is this correct?

73,
Paul
K5ESW


On Mon, Dec 12, 2016 at 8:13 PM, John Kaufmann <john.kaufmann at verizon.net>
wrote:

 > I have measured RF ground resistance for a short receiving vertical
(about  > 15 ft tall) with just a 4-foot ground rod.  I used the AIM-4170,
which is a  > pretty accurate instrument, although I won't claim it's
perfect.  On 160m  > the resistance is about 60 ohms.  As expected, the
measurement also shows a  > large amount of capacitive reactance, equivalent
to a series capacitor of  > about 50 pF.
 >
 >
 >
 > Actually I measured the resistance across a span of 1 to 10 MHz.  The
trend  > is for the resistance to decrease with increasing frequency,
although it  > reaches a floor of 25-30 ohms around 4 MHz and higher.  The
equivalent  > series capacitance is pretty constant across frequency.
 >
 >
 >
 > I would have expect the resistance to be higher with just a simple ground
> rod and it's possible there is some measurement error here. On the other
> hand the vertical is installed in an area that is surrounded by wetlands,
> so  > the soil conductivity is probably above average.
 >
 >
 >
 > 73, John W1FV
 >
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