[Moon-Net] 2M antenna matching Data

Edward R Cole kl7uw at acsalaska.net
Tue Nov 8 19:30:02 CET 2016


Curt,

I think you are experiencing normal receiving limitations of using a 
small array.  I looked up the specs for FO12 and FO13 on VE7BQH 
Antenna Chart and get this:
FO12 gain=12.48 dBd, G/T= -3.25
FO13 gain=12.92 dBd, G/T= -2.76

2x array gain =15.48 dBd or 15.92 dBd accordingly.

comparing with my M2 2MXP-20 gain=13.10 dBd, G/T= -2.61H, -253V, 4x 
gain=19.06 dBd

I have about 3 to 4-dB more gain in receive and that makes a lot of 
difference in what you can see on JT65.  When I was running qrp with 
150w I could always copy the single yagi stations better than they 
could copy me.  I had EIRP=135*150 = 20.2 kW and they might run EIRP 
= 32*600 = 19.2 kW;  both of us generating about the same signal in 
Tx.  But I had 3-dB more signal sensitivity due to having more 
antenna gain.  Of course if they ran 1x with 1000w that helped me 
even more 10Log(1000/600) = 2 dB.  Now days I run EIRP= 135*1300 = 175.5 KW

G/T is a figure of merit measuring how good your pattern is (how well 
does it reject ground noise).  This a factor of the design quality, 
so higher positive numbers are cleaner patterned antennas.  Look over 
the chart:
http://www.bigskyspaces.com/w7gj/6mTable.htm
click on second Tab for 144 antennas.

I am experiencing this same limitation using a single 6m yagi on 
eme.  The 2x and 4x array stations see my signal long before I see 
them.  Both stations running QRO.
My yagi gain = 10.85 dBd (13 dBi) and one needs 15 dBi minimum for 
doing 6m-eme (easier).  I can only see signals in my ground-gain elevation.

You should also try taking advantage of ground-gain (angle depends on 
height of antennas); probably good from 4 to 8 degrees 
(guessing).  My array is at 52-feet above ground so I see gg almost 
at MR or down to MS.

Hope this helps explaining your issues (a little).

73, Ed - KL7UW
I benefited from starting eme in 1998 when only CW was used and my 
array was minimum capable of eme with 1000w.  I made four contacts by 
CW before 2003 when I downloaded JT44.  All were super big-guns.

At 05:44 AM 11/8/2016, Curt Nixon wrote:
>Thanks for all the comments and directions folks:
>
>Regarding the data and its presentation, I can only say I copied it
>directly from the dispaly on the software utility.  Some of it I
>understand, and some not so much.  I am a newb with the Smith chart.
>The software is a data sampling and control utility for the T100.  It
>collects sweep samples over a range of frequencies and step sizes and
>loads them to a CSV file.  They are then used to plot a smith chart as
>well as an SWR, RL, and R+Jx charts.
>
>I believe the G is for Gamma which is (I think) the 50 ohm Smith
>normalized values of ZL.   I also think the "angle" shown is the angle
>of the vector at the given frequency and as the G point approaches 0+J0
>the angle becomes meaningless due to the minimum sample resolution  (25KHz).
>
>Anyway.  I have been using these two antennas for 2+ years and yes they
>are as near identical as my machinist skills (substantial) could build
>them.  The T match jumpers are at the ends of the T bars as someone
>suggested.
>
>They are oriented in the proper phase, and I cut the jumpers to less
>than +- 1/16" from same pc of LMR-400 Brand new.  My divider is one of
>the 1/2 WL  (1/4 +1/4) from square tube
>
>THey system has about 28 initials on it but perhaps I am still expecting
>too much from the pair.  During the first period of the ARRL weekend
>past, I could not detect a single station, including the mega stations
>which were operating.   Even when they worked, stations rarely had a
>hard time detecting me, but I can barely  see a trace for them.  System
>still shows less than about 1.2:1 SWR.
>
>So I decided it was time to start at the top and see if something is
>amiss...and it appears that, so far, not the antennas or feed+divider.
>I am next going to check the TR relay(s)  and will be working agin for
>the ARRL weekend in 2 weeks.   All the leaves are off the trees so that
>may help a little.
>
>Prior I will do some noise floor tests with the 50 ohm LNA terminated
>and see what it looks like.
>
>Again, thanks for all the support.
>
>As an aside, I believe my issues previously noted regarding the big KW
>paging system a mile away on 143.9 has been resolved.  It looks like the
>last of the antennas listed on that site have been migrated to DMRS on
>800MHz.  So I no longer see any of the intermod junk.
>
>Curt
>KU8L
>
>
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>
>
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73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
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