[Fourlanders] 2m Antenna comparison

Wed Dec 31 00:57:00 EST 2014

I concur with both Ron and Sherman.  You can't really compare the two antennas without understanding the differences in the feedlines.  It the two stacked 2M9SSB antennas really have 3dB+ of feedlines loss (that is a lot by the way) then the EME antennas might have a significant advantage.  If you really want to investigate this Bob I would look at the differences between the two feedlines.  If you still have Kim's toy you could start by sweeping the two lines for impedance mismatches then look at return loss, insertion loss, etc.  If nothing else you might find a bad connector or coax.  To Sherman's point, there is relatively little skyway propagation  at 2 meters and up except on the rare occasion of sporadic E MUF getting that high.  As a result most of your signals will have low takeoff angles.  Once you are 20 feet above the earth your 2 meter band antenna is up 3 wavelengths and there is little effect of the earth on takeoff angle.  The value of any increase in height above that is from clearing obstructions that may cause shadowing.  My 2 cents.

73
Jim, W4KXY

Sent from my iPad

> On Dec 30, 2014, at 6:17 PM, Sherman Banks <w4atl at shermanbanks.net> wrote:
> 
> I would think the take off angles to be more significant at 6M than at 2M. Remember my analysis was at 6M.
> 
> For those interested, the analysis of Bob's QTH that I gave at the 6M BBQ can be downloaded at aa4xg.com.
> 
> 
> 
>> On Dec 30, 2014, at 11:25 AM, Ron Rogers <ww8rr at charter.net> wrote:
>> 
>> 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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