Summary (tl;dr): This week I’ve been testing various antennas from the same location on the same observations, directional az/el yagis vs fixed low-gain yagi vs discone. A fixed yagi pointing up produces great results but still not yet strong enough to decode much on data links in my configuration. Keep reading for more.
I stumbled across station 488 by @W7KKE a while back, and he seems to have great success with a 3 element UHF yagi pointed straight up (plus a low noise amplifier), using a high “minimum horizon” of 40 degrees. This led me to wonder if our conversations about fixed stations using omni antennas such as turnstiles is not the best way to go about things.
So I got to testing this past week, with the following configurations (as of 2019-05-27 if you’re looking through my observation history):
Station 2: Az/El rotation, M2 cross-element yagis on UHF and VHF fed into an MFJ diplexer before a low noise amplifier, then 100ft of LMR-400 into the SDR (which is typically USRP B200 Mini, but more on that later)
All 3 stations set to a 40 degree minimum horizon, and initially all 3 stations set to capture the same observations from the same location.
Some initial results (Az/El M2 yagis, usrpb200, LNA … vs dual vhf/uhf yagi fixed … vs discone):
FOX-1B, 3.5 min 64.0° pass
Station 2 (38 DUV frames, good audio almost throughout)
Station 300 (2 DUV frames, some spots of good audio near center of beam)
Station 767 (no DUV, one spot of weak audio near horizon)
There are a lot more observations from this portion of the test, click here.
Is there a USRP B200 advantage over the RTLSDR?
At this point I took the discone offline so I could use its rtlsdr on Station 2 to see if there was an unfair advantage with the USRP B200? Summary: No noticeable difference.
RTLSDR vs RTLSDR (Az/El M2 yagis, LNA … vs dual vhf/uhf yagi fixed):
Is the LNA an advantage?
Most certainly yes. I dug up a PGA-103 based LNA and put it in front of the rtlsdr on station 300 as of 2019-06-01 15:00, dropping the gain back down to default. However, I’m still not decoding data frames as well as station 488 is. At this point given the small horizon I’m hitting a bit of a drought before more data downlinks pass, but here are some initial results:
SO-50, 4min 75.0° pass
Station 2 (good audio almost throughout)
Station 300 (decent audio through about 75% of the pass)
(resist the urge to compare this with the audio of FOX-1B above, as they downlink on different bands)
NOAA 19, 3.5 min 57.0° pass
Station 2 (clear image, no difference from the results of NOAA 18 + usrpb200 above)
Station 300 (a little bit of artifacts, but better than the NOAA 18 pass with no LNA above)
I have some other observations between the two in this configuration that you can dig through here.
At this point I’m anxious for another Unisat-6 pass to see if it would decode now but at such a small window/horizon that’s not going to happen for a while. Hopefully I can get @W7KKE to chime in with the secret sauce to his fixed setup.
Interested in your thoughts and ideas here, and other possible combinations for testing. I don’t have much experience with the PGA-103 LNA so at some point I may want to swap it in on Station 2 to see if it under performs compared to what I’ve got in there.