Topband: 2-el array SWR question (160m)

[Mike Smith VE9AA]

Today I installed 160m vertical #2 in what will soon become a Comtek PVS-2
(2el BS/EF) array for 160m. (vy recently I installed 3 Comtek (wire)
4-squares for 20, 40 &80m.

Spacing is about 134’ for these two 1/4wl 160m antennas. (oriented
NNE/SSW-best I could do, given the property here)

 

With 3 of these wire (4-el) array’s now under my belt, I measured very
carefully today with some confidence and cut all my wires accordingly
thinking I was done.

 

This 160m antenna is all wire and configured as an inverted L, same as the
original (ant#1).  Two raised radials only 90º apart (not 180º)  around
6-10’ off the ground in the woods (varies with what trees I could find for
supports and they zig zag a little bit at the far ends for around 15’ due to
property line constraints).  They “Gull-Wing” a very little bit at the PVC
hub where the vertical itself and coax and 2 raised radials all meet.

 

When I checked the SWR on the new antenna (#2) with my AA-230pro I was a
little surprised to find out my math wasn’t quite as good as I have enjoyed
on my 3 previous  arrays.

 

SWR was ~1.5:1 or so at 1770kHz
.not quite what I had calculated. (by the
3rd array I thought I was getting pretty good at the math and had it
virtually bang on freq and flat as a board on the desired frequency)

My original vertical’s (#1) SWR remained virtually unchanged, pretty much
flat at 1835kHz
The original (#1) has a mile(1.6km) of in&on ground
radials
..Antenna #2 just has the 2 raised radials

I don’t have the PVS-2
relay box situated or two coax or control line(s) run to the center
yet
.more work for the coming days.

 

So my first question is, once I am feeding them with the PVS-2 box, will the
resonant frequency of both rise or is simply the proximity to one another
what causes the SWR to rise in these arrays? 

 

It’s probably pretty easy at this point to tweak the just-installed
vertical’s (#2) SWR to dip precisely @ 1835 like the other one by adjust
some of wire lengths (either radials or the vertical itself), but I’d rather
get it right the first time, rather than trying to add wire later !

 

My 2nd question is I know (now!-oops) this type of array is supposed to be
fed with two equal 50 Ohm cables, but I only have 75 Ohm on hand.  How bad
do you think the SWR will be affected? (I just don’t have the $$ right now
for a big spool of 50 Ohm coax, so will use what I have on hand.

 

I should mention there is a LOT of clutter 50’-150’ to the north of this
160m 1/4wl vertical (three 4-squares, other wire antennas, etc.) so maybe
this 

has affected the SWR and my Casio calculator is not actually broken?)

 

Thanks for any advice from the collective.

 

Mike VE9AA

 

Mike, Coreen & Corey

Keswick Ridge, NB