rvmills
Well Known Member
A quick call to the FCC today yielded a shiny new tech license (as yet virtual, but legal just the same). It was very timely, having just buttoned up after installing the APRS below the panel, and the Ryan Howell J-pole antenna in the right gear leg fairing.
VAF's "guccidude1" Dan came by with his null modem cable, and assisted (or supervised, depending on who you ask) as we configured both profiles on the MT8000FA.
I then launched on two quick flights...one using the J-pole, and one using the Comant belly whip (stolen from COMM2). I was a bit skeptical about what we'd see with the J-pole being so close to so much metal (the gear leg and the engine mount...pics of that install are in this thread).
However, I was pleasantly surprised by the results. I have some more testing to do, and am certainly open to ideas from "Team APRS". The short version is that it appeared to transmit good positons/tracks with both antennas (though the whip looks stronger, as was expected). I also tested the Primary and Secondary profile on each test, by running primary on the way out (shows MIC-E "En Route"), and switching to secondary (shows MIC-E "Returning") on the way back in. Pretty cool stuff! If you want to look at the tracks on aprs.fi, the link to my APRS track is now in my signature block.
Here are a few screen shots.
The first is both tracks superimposed. Both flights were at 8500' MSL (approx 3-4K' AGL). The inside circle is the J-pole flight, and the larger circle is the external whip flight.
Looks like the whip was a bit more consistent with its position reports at altitude, though both antennas performed well when smart beaconing.
Where I saw the biggest difference was back at Stead in the pattern. I only did one landing with the J-pole, and three with the whip, but the J-pole dropped me as I turned downwind, while the whip kept tracking through the three circuits. Here are two shots zoomed in at Stead with TO and LNDG(s) for each flight. (I took off R-L on 26, turned right and departed to the NW...off screen right. Then came in from the upper left on the 45 to right traffic for 26).
First the J-pole:
Next the whip:
Pretty marked difference...though I'm hoping that the J-pole will show more, given "equal time" in the pattern. I will go out tomorrow and do some more test runs, and do some more low work, to test the performance more fully. I'll also swing by the avionics shop on the field and do some SWR testing of each antenna combo, to see what it shows.
If Sam, Pete, Allen, or any other APRS gurus have any ideas on tuning, or other measures to increase effectiveness, I'm all ears.
Given my desire to do live APRS tracking during SARL races, the low altitude performance is a key factor. I'd feel pretty good tracking normally (X-C etc) with the J-pole, and could use the whip for racing only (don't need the SAR radio then!)...however...
I did have a downside with the whip. Every time the APRS transmitted with that antenna, it broke squelch on my SL-40 (Comm1). Just a short burst as the packet was sent, but it'd be very annoying, long term. And when I was monitoring approach and later ASOS on the SL-40 STBY freq, when a packet launched and the SL-40 broke squelch, the STBY freq muted. So that is a no-go, till I get it resolved.
gucci Dan suggested I just turn up the squelch...will give that a try tomorrow.
The antennas for COMM1 and COMM2 are 28 inches apart, and line abreast on the belly. Not sure if that is a factor. I've not yet used the SAR radio in flight, so I do not know if it causes similar interference with COMM1 (we can't get the radio programmer and my schedule in sync, and I can fly missions without that radio, so just not done yet.)
Both antennas on the belly are COMANT 122s, and the SAR antenna has not been trimmed (still 22" long). I have another CI-122SP that I can trim down for 2 meter 1/4 wave and swap in for COMM2/APRS, and perhaps that will stop the RFI...not sure.
Will report back on further testing, and open to any suggestions ya'll may have!
Cheers,
Bob
VAF's "guccidude1" Dan came by with his null modem cable, and assisted (or supervised, depending on who you ask) as we configured both profiles on the MT8000FA.
I then launched on two quick flights...one using the J-pole, and one using the Comant belly whip (stolen from COMM2). I was a bit skeptical about what we'd see with the J-pole being so close to so much metal (the gear leg and the engine mount...pics of that install are in this thread).
However, I was pleasantly surprised by the results. I have some more testing to do, and am certainly open to ideas from "Team APRS". The short version is that it appeared to transmit good positons/tracks with both antennas (though the whip looks stronger, as was expected). I also tested the Primary and Secondary profile on each test, by running primary on the way out (shows MIC-E "En Route"), and switching to secondary (shows MIC-E "Returning") on the way back in. Pretty cool stuff! If you want to look at the tracks on aprs.fi, the link to my APRS track is now in my signature block.
Here are a few screen shots.
The first is both tracks superimposed. Both flights were at 8500' MSL (approx 3-4K' AGL). The inside circle is the J-pole flight, and the larger circle is the external whip flight.
Looks like the whip was a bit more consistent with its position reports at altitude, though both antennas performed well when smart beaconing.
Where I saw the biggest difference was back at Stead in the pattern. I only did one landing with the J-pole, and three with the whip, but the J-pole dropped me as I turned downwind, while the whip kept tracking through the three circuits. Here are two shots zoomed in at Stead with TO and LNDG(s) for each flight. (I took off R-L on 26, turned right and departed to the NW...off screen right. Then came in from the upper left on the 45 to right traffic for 26).
First the J-pole:
Next the whip:
Pretty marked difference...though I'm hoping that the J-pole will show more, given "equal time" in the pattern. I will go out tomorrow and do some more test runs, and do some more low work, to test the performance more fully. I'll also swing by the avionics shop on the field and do some SWR testing of each antenna combo, to see what it shows.
If Sam, Pete, Allen, or any other APRS gurus have any ideas on tuning, or other measures to increase effectiveness, I'm all ears.
Given my desire to do live APRS tracking during SARL races, the low altitude performance is a key factor. I'd feel pretty good tracking normally (X-C etc) with the J-pole, and could use the whip for racing only (don't need the SAR radio then!)...however...
I did have a downside with the whip. Every time the APRS transmitted with that antenna, it broke squelch on my SL-40 (Comm1). Just a short burst as the packet was sent, but it'd be very annoying, long term. And when I was monitoring approach and later ASOS on the SL-40 STBY freq, when a packet launched and the SL-40 broke squelch, the STBY freq muted. So that is a no-go, till I get it resolved.
gucci Dan suggested I just turn up the squelch...will give that a try tomorrow.
The antennas for COMM1 and COMM2 are 28 inches apart, and line abreast on the belly. Not sure if that is a factor. I've not yet used the SAR radio in flight, so I do not know if it causes similar interference with COMM1 (we can't get the radio programmer and my schedule in sync, and I can fly missions without that radio, so just not done yet.)
Both antennas on the belly are COMANT 122s, and the SAR antenna has not been trimmed (still 22" long). I have another CI-122SP that I can trim down for 2 meter 1/4 wave and swap in for COMM2/APRS, and perhaps that will stop the RFI...not sure.
Will report back on further testing, and open to any suggestions ya'll may have!
Cheers,
Bob
Last edited: