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

Fri Jan 17 10:11:26 CST 2014

Jay,

I'm glad you ask that!

The location of the  test system is actually 1 mile away from my normal operating position in a secure location, operating within my grant which allows fixed operations up to 10 km from the granted location.  At the site, the grant is posted and current copies of Part5 and part2 are available in accordance with Part 2 and part 5.  I do maintain positive control of the beacon and can kill it remotely but have to start it again manually.  For much of the time, the master antenna has been detuned with occasional monitoring using it but most listening has been with the K9AY loops directed to the NE.  I've not been uploading spots because I wanted to get some unimpeded screen shots of the WSPR map.

In order to get the match closer to 50 ohm under the circumstances, I put a 1200 pF silver mica cap to the ground rod off of one of the coil taps...it worked out to around 42 -j10 in the end which neither the amp nor the U3 seemed to care about.

Hope that helps!

73,

John XIQ

________________________________
 From: "jrusgrove at comcast.net" <jrusgrove at comcast.net>
To: 600mrg at w7ekb.com 
Sent: Friday, January 17, 2014 9:56 AM
Subject: Re: [600MRG] U3 Experiment phase one initial results (long)

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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