ATGP 2013 - Stony Man - 22 July 2013
What an interesting day on Stony Man. We got there in plenty of time.
We set the 2m antenna up slightly in the woods to be out of other folks’ way. That was a bit of a problem last year. After a quick install, we attached the coax to the diplexer.
I lost my nice collinear 440 antenna so brought along a “connector” monopole with bent down leads, measured to 440 with my trusty wavelength measuring tape, bend the tip, hung it on a small tree branch and hooked up the coax to the diplexer.
I connected the coax to the radio, hooked up a battery expecting this would be a cinch… because nothing changed at all from last year.
I did expect that makeshift 440 antenna to not produce as good results as last year, but figured there was plenty of margin.
So… I fired up the rig and loaded PM3 (same as last year) and made a few edits to status messages.
We were early so didn’t hear much for quite a while. Soon Dave from Apple Orchard 5 gave a shout on 445.925. We responded on the 710. Nice signals both ways, not bone crushing, but adequate. I thought to my prideful self… “Awesome, VHF will be even better especially with the bigger antenna.”
I heard Dave’s APRS packets just fine. He could not hear a thing from me. Hmmm… transmit UHF on sloppy antenna good… transmit VHF on better antenna nonfunctional.
Later, Dick came online with Maryland Mountains 7. Same thing… booming voice signals on 445.925 and very weak to almost nothing heard from us on VHF. His APRS packets boomed in to us without problem.
So there we were wondering if we weren’t digipeating or something. Eric monitored my VHF APRS transmit signals and they were there. I switched over to PM2, my regular mobile setup, and quickly received many ACKs of my beacon. I switched back to PM3.
Then Eric and I tried another 2m/440 antenna. Same result. UHF rocked, VHF transmit didn’t.
We tried Eric’s voice radio on his antenna. Same result. UHF rocked, VHF transmit didn’t although both AO5 and MM7 heard a faint FM voice from us.
Arggggg…
We moved the 2m antenna back to the rock tip and removed the diplexer… VHF antenna was now straight to the APRS 710. Eric handled UHF with his radio.
Same thing. I could receive APRS VHF packets easily, but no one could hear us. In fact, by this time, I can say I heard beacons from station 2 to 9.
Dick from MM7 diagnosed his A-Band receiver was deaf and moved the APRS functionality to the B-Band. Now MM7 could hear my packets with the greatest of ease.
I could also hear GDHill 8 packet chatter quite easily although I don’t know if it was strong enough for APRS.
AO5 still could not decode packets from us although I think he said he could hear them. So while Dick’s receive was a problem there was still something odd going on with propagation.
Finally, I simply upped the APRS VHF power to 50 watts.
Everything worked… well enough.
Every functional check I made on the antennas suggest they were working just fine. Once the receiver issue at MM7 was resolved, Dick and I had the usual solid signals on both UHF and VHF. This left the link between Stony Man and Apple Orchard to wonder about.
It’s easy to see why UHF signals from AO5 to SM6 might be stronger than VHF… Dave has a very big collinear antenna with, I think, 3 phased portions for VHF and 5 or so for UHF. That should mean a slight gain advantage.
It doesn’t explain why Dave could not hear us on VHF very well despite our antenna and radio swaps. I don’t think his VHF receiver was deaf since he could hear Station 4 just fine.
So the end result is, we did get things working and have already scouted out a slightly higher spot on Stony Man to favor Apple Orchard a bit better next year.
Plus the fact the UHF link between SM6 and AO5 with a dinky antenna hung on a branch completely blew away the big VHF link with its stately, bigger, better antenna.
It sure looks like a VHF transmit problem from Stony Man. A problem in common with two radios and two antennas in every combination.
Fun.
John Huggins, K4XO
Regarding Stoneyman to GSD hill direct packets:
Stonyman was heareding GD Hill reliable with one bar. Note, I put 10 Watts to the Maryland Mountains because that was more than enough. At some point I move my antenna and upped the power to 50 Watts so AO-5 could hear me. This was overkill for Maryland Mountains.
So I was ten watts at first then 50 later. This could account for you seeing me with two bars while I saw you with one.
John said:
I get -19 dB from the point where 95% occurs. I’d say more like 65% probability is what I’m seeing with Radio Mobile.
As far as average signal strength goes, however, it says two bars… just like you saw.
I saw a reliable and repeatable 1 bar from you so we were pretty well symmetrical. In fact once things settled in, south bound packets got into a rhythm of weak packet (from GDHill), booming packet (MMtns), digipeat from me, and then one more packet heard (I guess from AO MTN.
John
I’ll need to look at KD6AKC’s log again to see if I ever decoded you straight.
On Mon, Jul 22, 2013 at 11:11 AM, Bob Bruninga bruninga@usna.edu wrote:
John, just curious what the link looks like from Stonyman to GD hill, since I heard them at 2 bars and decoded some of their packets. I dont plan on skipping MDMTN, but just curious what your LINK calculator gives for this link for comparison to my actual results.
Bob. Wb4aPR