[Fourlanders] 2m Antenna comparison

[Ron Rogers]

OK...here's my initial thoughts without further facts to confirm or refute.

The only way to truly compare antenna performance is by using the same feed
line for testing of both antenna sets. I would say that the majority of the
signal difference is due to differences in feed line loss of both antenna
arrays.

If I remember correctly, the feed line going to the horizontal antennas on
Blackhawk is made up of about 150' of LDF4-50 (2 pieces with a jumper),
50-60 feet of untested RG-8 "something" from the hard line up to the
antennas, another short jumper in the shack, etc. If everything was perfect
and met specs, that's at least (theoretical) 3.8 db loss in the feed line
run at 144 MHz. and that's significant !

Until you actually measure under some power with a pair of calibrated Bird
43 meters at each end of the individual feed lines you will not know what
your true system losses really are.
 
At this point I would have to say that the EME antennas having much shorter,
and newer feed line give them the real advantage, no matter what the height
is.

Ron
WW8RR

-----Original Message-----
From: Fourlanders [mailto:fourlanders-bounces at contesting.com] On Behalf Of
w4zst at windstream.net
Sent: Tuesday, December 30, 2014 10:43 AM
To: fourlanders at contesting.com
Subject: [Fourlanders] 2m Antenna comparison

Here's some interesting results for the group to ponder on.

Johnnny's 2m EME antennas have been up here at my QTH for about 3 months
now.  They are two M2 2MXP20 cross-polarized antennas mounted on his tower
trailer with an AzEl rotor, 12' separation on a horizontal boom (fiberglass
extensions).

We have used them exclusively on horizontal polarization so far for all the
EME Q's we've made, because I was using my transverter with common output
rather than his with separate RX and TX connections.  This was done for
trouble-shooting purposes as we had some problems with his preamp and
transverter and I had bypassed the H-V relay for convenience.

Last week, Johnny and I put up the club 2m beams for the contest.  The pair
of M2 2M9SSB antennas that we have been using on the BlackHawk tower trailer
stacked vertically and at about 45 feet right now.

What I found interesting and would like your observations on were the
results I had on last weeks Monday night 2m net.  I had an AB switch from
the 2m station to be able to switch between the contest antennas and the
horizontal EME antennas.  Note that the EME antennas are only about 20'
high.

I followed the net control stations directions and copied almost every
station that checked in from EL96 to EM77 and couldn't tell any difference
switching between the two set of antennas.  The only two net check-ins that
I couldn't hear were uncopyable on both sets of antennas.  those stations
were North of Charlotte.  Of course, since net control is about 65 miles
East of me, there would be times that stations pointing toward him might not
have been optimum for me.

Anyway, I was pretty surprised that the much lower EME antennas performed so
well here.  Maybe it has to do with the pretty rapid dropoff of terrain from
the hilltop.  That's what Sherman said was the reason he recommended the
height for the 6m antennas, both here and from the mountain.  All the leaves
are off the trees right now too, so that may also be a factor, but I've had
Johnny's antennas on for the monday night 2m net many times in the last 3
months before they started falling.

I have copied the FL checkins to the net off the side of the EME antennas,
copied stations in central AL off the back and even the station in EM77 in
KY off the back of the antennas.

I am planning to leave the 2m EME antennas and station set up for the
contest as it is expected to be a good condition EME weekend and we may be
able to get some good multipliers out of it.  I also plan to listen with
that station while Kos is on 2m with his station and the contest antennas,
just to make some futher comparisons.

I also copied K8TQK last night 59 on the EME antennas, pointed right in to
the house!!

Either the 2m EME antennas are magic or the height is special.  It does make
me want to get a pair of them for myself to set up here permanently for both
EME and terrestrial!!  And actually so far, they've only been used with
H-pol.  I did change them last night to V-pol when I had about 50+ degrees
elevation and sigs off the moon were stronger with V-pol.

Let me know what you think about this antenna situation.

Thanks, Bob

 
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