[600MRG] U3 Experiment phase one initial results (long)

[jrusgrove at comcast.net]

John

Thanks for sharing the results of your test. A couple questions.

1) Was the "large master antenna" for 630 meters shorted to ground or detuned?

2) Please explain "1200 pF of capacitance to get the 50 ohm match".

Jay W1VD  WD2XNS  WE2XGR/2  WG2XRS/2


----- Original Message ----- 
From: "John Langridge" <jlangridge at sbcglobal.net>
To: <600mrg at w7ekb.com>
Sent: Friday, January 17, 2014 10:33 AM
Subject: [600MRG] U3 Experiment phase one initial results (long)


Good Morning:

Last night was a really solid night for this little experiment (1000 spots hearing my 50 mW ERP to a 
different antenna than normally used here) that I have been running for myself over the past week 
and I wanted to share some very initial results as I go through the data.

My focus has been on S/N values that would be able to yield a QSO where meaningful information could 
be passed (more than just beaconing alone). JT9 seems to bottom out around -24db so I set that as 
the lower limit. I still need to look at consecutive reports better than -24 and will have to work 
up some queries to accomplish that but there were almost 700 reports greater than -24 and that was 
not limited to ground wave signals as reported from the guys in OK. XJM reported 166 spots, XNS 
reported 33 spots along with a multitude of others on the sky wave path. The ground wave was solid, 
as expected, within a 250 miles radius, as reported by XXM, UV, JIA, GX in OK and AA5AM who is only 
51 mile away. Other keyboard modes like Thor, GMSK, PSK(?) and even CW were very easily represented 
by the signal levels reported, both skywave and groundwave).I have a lot more to look at here so for 
me personally, this is just the tipping point.

The antenna used in this experiment is a 25 foot tall 20m inverted Vee (sloping wires @ 45 degrees, 
in-line, broadside to the NW/SE) fed using ladder line as a marconi. There were only 4 radials, 3 of 
which were less than 30 feet long and another that was 50 feet long but wound around to fit in the 
small space provided. A chainlink fence (at a range of 15 feet) surrounded the antenna, which was 
attached to a fiberglass pole lashed to a pecan tree. There was a ground rod at the feed point as 
well as at the transmitter entrance. The system was resonated with a hurriedly-wound variometer on a 
5 gallon bucket, secured with electrical tape and elevated on two cinder blocks. The system required 
about 1200 pF of capacitance to get the 50 ohm match but it was a simple process and I admit that I 
did not calculate any values for this - I simply wound it and put a tap every few turns. Initial 
tests were with the U3 alone with 2 extra BS170 FETs running
 between 1 and 2 watts to the coax for a (corrected) ERP of no more than 10 mW. The improvement I 
made on Thursday was the addition of a small amp, running about 10 watts into the coax for an 
increase ERP of 50 mW.


Ground conditions here are actually quite good. FCC maps show 30 mS/m average here which abuts an 
interface with 15 mS/m average to the west at the bottom of the escarpment. No doubt this helps.


So for me having used the large master antenna for my 1w ERP operations on the band over the last 
year+, this was a significant surprised to me even though I had read the reports of guys running 12 
foot radiators with coils from the balcony of an apartment complex and being heard across country on 
WSPR or somesuch. I had to see it for myself. And for that matter, that information is not readily 
available for the casual passerby that was curious about the band. In fact, that is what 
precipitated this experiment. After a number of talks and discussions about the band at club 
meetings and hamfests, the question that always came up was how someone who lived in a small lot, in 
a condo, or perhaps only had a G5RV could get on the band and be successful. While there are a lot 
of guys who have had really great success with very small loops and thus not concerning themselves 
with radial systems, this data seems to show that one might be able to get away
 with very little radial system and still experience some success. Additionally, the construction 
portion of this project was intentionally completed very haphazardly because I know a lot of the 
guys asking these questions and how they do things so I was hoping to interject as many problems as 
possible. As long as voltage was respected(just under 1000v at less than half an amp while running 
the amp) there were no problems and this is obviously a big part of using a very compromise system.


So while none of this information may be earth shattering, it gave me personally some data to work 
with when I am asked the question about how someone can run this band with minimal conditions. No 
doubt it can be done. It would be interesting to see similar experiments duplicated from different 
locations as I have a favorable location here for lots of activity in all directions.

Going forward I am going to test some other compromise, bare bones antenna designs, possibly 
starting as early as tomorrow afternoon and I will post details about that. The U3 continues to run 
at 10 watts to the coax and will probably run over night in the same configuration. I do have pics 
of the setup if anyone is interested in seeing them.


So that's my ramble. I know there was very little "new" here that has not been uncovered by someone 
else earlier but I needed this information for dealing with the hams I deal with as they prepare for 
something at some point on this band.

73 and thanks for the bandwidth... much more to follow as I wade through this data and begin the 
next phase on this project.

John WG2XIQ/KB5NJD
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