Topband: Help With 80M Array

[john battin]

When you switch directions do you see any (even slight) change in the swr or power into the dummy load??? How far do you have to move the frequency before you see power increase in the dummy load??
John
K9dx
 

> Date: Tue, 11 Dec 2012 16:13:09 -0500
> From: olinger at bellsouth.net
> To: wewill747 at gmail.com
> CC: topband at contesting.com
> Subject: Re: Topband: Help With 80M Array
> 
> That sounds more like relays are not being gotten voltage out at the PVS
> switch unit. 1,2,3,G all have to be separate wires to the controller.
> Particularly suspicious like G may be mixed up with one of the 123 guys,
> which would keep any operating voltage from the relays. If you had to do
> any cable splicing and different wire colors on the two runs, that would be
> suspect.
> 
> 73, Guy.
> 
> On Tue, Dec 11, 2012 at 2:01 PM, Wayne Willenberg <wewill747 at gmail.com>wrote:
> 
> > I recently bought a Comtek 2-element phased vertical array system for 80M.
> > Each vertical is ¼ wavelength in length and the 2 verticals are spaced ¼
> > wavelength apart.
> >
> >
> >
> > I have installed 60-- ¼ wavelength radials in a uniform and symmetrical
> > pattern around the base of the first vertical. Using my AIM 4170 analyzer,
> > I adjusted the length of the first vertical until the minimum SWR was at
> > the frequency I wanted (3.71 MHz). At that frequency, the SWR was 1.4 and
> > the series resistance at the feedpoint measured 35.7 Ohms with a series
> > reactance of 6 Ohms. (If you are curious, the resonant frequency was 3.68
> > MHz.)
> >
> >
> > Next, I assembled the second vertical, making each section and the overall
> > length the same as the first. I then erected the second vertical in a SW
> > direction of the first vertical at a distance from the first vertical of ¼
> > wavelength. I used a transit to make sure the base of the second vertical
> > was at the same elevation as the first vertical.
> >
> >
> > I then installed 60-- ¼ wavelength radials in the same manner as the first
> > vertical. Where the radials of the 2 antennas overlapped, I cut them and
> > soldered them to a 3” piece of copper strip that runs at a 90 degree angle
> > to a reference line connecting the 2 verticals.
> >
> >
> > To make sure the two verticals behaved the same way electrically, I
> > connected my AIM analyzer directly to the feed point of the antenna being
> > tested with 50 feet of coax. (The 50 feet of coax was calibrated out of
> > the measurements.) In taking these measurements, I lowered one antenna to
> > a horizontal position and measured the one vertical that was upright. I
> > then reversed the process. Next I superimposed the scans of both verticals
> > over a frequency range of 3.0 to 4.5 MHz. The traces for the SWR, Theta,
> > and the return loss only varied slightly from each other. For example, the
> > SWR of the first vertical was 1.4 and it was 1.45 for the second vertical.
> >
> >
> > Next, I located the relay box, that contains the hybrid coupler, between
> > the 2 verticals and connected the relay box to each antenna with RG-213
> > that is electrically ¼ wavelength long. I then ran RG-213 from the
> > transmitter port on the relay box back to my shack. I also ran another
> > length or RG-213 from the”50 Ohm Load” port back to a 50 Ohm dummy load in
> > my shack. (All of the RG213 I used was new.) I also ran the control line
> > from the 3-position control box in my shack to the rely box. Finally, I
> > checked the continuity of all of the wiring and also made sure the relays
> > closed or opened in response to the signal from the control box.
> >
> >
> > After all of this effort and expense, I am very disappointed in the
> > performance of the array. I can’t measure the RF output in the NE or SW
> > endfire positions to determine if I am getting any gain, but when I listen
> > to stations in Europe and switch between the NE and SW positions, I can’t
> > see or hear any change in the signal strength. So, I question whether
> > there is any front to back rejection.
> >
> >
> > I returned the relay box to the vendor. They checked it and said it was
> > working correctly.
> >
> >
> > I have used my AIM analyzer to scan the feedline at my shack when the array
> > is in an endfire position. From 3.5 to 4.0 MHz, the SWR slopes downward
> > from 2.5 to 1.5. There is no resonant point, and Theta starts at -30
> > degrees and curves upward to -5 degrees.
> >
> >
> > I increased the frequency scan range and found a distinct null in the SWR
> > at 3.4 MHz. At that frequency, Theta is 0 and the return loss is at the
> > bottom of a very deep “V” trace and measured -36dB.
> >
> > Based on these measurements, it seems to me the mutual coupling between the
> > 2 verticals has moved the minimum SWR and the resonant point of the array,
> > in an end fire configuration, to a point well below the 80M band.
> > *QUESTION
> > 1*: Am I misreading these results?
> >
> >
> > After reading and rereading the chapter in Low Band Dxing on Arrays, the
> > advice is to use 75 Ohm, instead of 50 Ohm, coax for the ¼ wavelength
> > feeders. So, *QUESTION 2*: should I try RG11 with PL-259 connectors? (I
> > use a 1.5KW amp on 80M and the maximum voltage rating for RG11 is 300V. Am
> > I safe using RG11 or should I try LM-400-75 that has a 2,000V rating?)
> >
> > *
> > *
> >
> > *QUESTION 3*: Also, is it OK to put 50 Ohm connectors (PL-259’s) on 75 Ohm
> > coax?
> >
> >
> > *QUESTION 4:* What other tests or measurements should I try to improve the
> > performance of this array? (I do have a dual trace scope, if that would be
> > useful).
> >
> >
> > I’m sorry this post has gotten so long, but I wanted to explain everything
> > I did and the measurements I made.
> >
> >
> > Thanks in advance for any help you can give me.
> >
> >
> > Wayne, KK6BT
> > _______________________________________________
> > Topband reflector - topband at contesting.com
> >
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