[VHFcontesting] The Band Is Closed? There's an app for that.
les at highnoonfilm.com
Fri Nov 20 11:40:50 PST 2009
VHF Men who have had a chance to read a few issue of DUBUS magazine may have noted that Meteor Scatter operators in Europe put a lot more emphasis on manipulating the WSJT software to achieve successful contacts than we do in North America. That's a very general statement, as there are certainly some very skilled WSJT operators in the US and Canada as well...but for most it seems to be a casual experience. They're quite content to sit back and let the software do most of the work and rarely attempt to manipulate it to their advantage.
Others use the software infrequently, perhaps only during major showers, and don't take the time to unlock it's full potential.
Recently, Harry Johnson, WB3BEL wrote a very compelling response to a discussion about this topic on the WSJT reflector. For anyone interested in the mode, it should be required reading. Following some of the techniques that he outlines will make you a better WSJT operator, and you'll put more contacts in the logs. With his permission, I'll share an edited version of those remarks now:
I agree that while the physics and geometry tend to debunk the notion of "one-way" rocks. The term will endure to describe the frustration due to one party decoding more pings the other. I will say I am by no means an expert, but I have a few observations that may benefit others.
It would be true that if the mode were full duplex and both stations had similar effective ERP and G/T you would both receive reciprocal reflections off of the same physical meteor trail. But, that really isn't how we run on MS. We run simplex mode. So it is probable that if the meteor pings are short and/or few, one station receives more than the other.
However, if this does not appear random over a long time period you may want to investigate why.. If you more frequently receive fewer pings than your partner or you often take longer to move to the next message than they do, and you have similarly equipped station it's worth investigating.
I'd say that most of the major reasons have a common basis; poorer signal to noise ratio. It may be you have high local noise, it may be that you have less skill using WSJT controls or decoding using your eyes and ears. Or it may be a defect in signal quality.
If its local noise you will have a struggle. An antenna with lower sidelobes may help. Finding a quieter freq may help. Finding the source and neutralizing it is your best option but may be difficult or an ongoing battle. Sometimes pointing off direct bearing by both parties can help especially on short paths.
If you have a big frequency error either TX or RX the decoder will be less sensitive. The solution may be to start a sked with Tol = 400 and progress to lower Tol (200, 100...etc) after receiving the first bursts and adjusting VFO if early in sked or RIT if later. What you are trying to do here is get the DF low and then tighten the Tol. You don't want to change your freq if the other station has also made a correction. This is a bit of mind game. For example, if I have only run a few sequences and RX a fragment of other stations TX1, and see a big DF say +250. I can fairly safely assume that they have not seen me with a big -DF and counter corrected. I will move my VFO +250. and then lower Tol to 200. But if its later in the QSO and say I RX the other station TX2. I might just move the RIT assuming they may also have made a change on their side. So being a better operator may improve success here.
WSJT is NOT as sensitive in decoding SH tones as your brain using eye and ear. If you set WSJT to be super sensitive to SH tones (choosing low clip value) you WILL get false decodes and result in some busted contacts. Tiny noise spikes will sometimes decode as SH tone. But listening for specific tone using headphones and looking for a trace line at the right vertical position on the SpecJT in combination with the WSJT decoder for SH is many more dB sensitive and less prone to false decode. If in doubt, you can click on the region on the specjt trace to encourage multiple decode using different start time for the captured data. Or you can wait for a second confirming ping. I find that WAY FEWER THAN HALF of decodable SH messages automatically decode in WSJT. Know how to adjust the RX level close to 0 dB, and understand how some noise blankers/AGC reduce sensitivity to short fast rise time pings.
I don't fully understand it, but if I am listening using headphones and discern a definite meteor ping especially TX1 or TX2 with data, I will relentlessly click on it or slightly before and after it in time until I squeeze some useful characters out of it. It's like...I know you are hiding in there...and I am going to beat on you until you give up a few letters. These reluctant to decode pings come from signals with lots of impairment. They may be for example (not exhaustive):
1. Very weak (1 or 2 dB),
2. Very strong /without a sharp rise time
3. Have a big DF.. or a lot of time varying doppler..
4. TX/RX station has a lot of hum, distortion, sound card jitter on signal...
So also it depends on how hard the operator on the other end is trying. If you walk away from the screen to get a coke, watch TV you will get fewer decodes than a skilled op trying to choke every character string out of the ether...Some guys want to see the full message in a decode. Other guys will mentally glue call fragments together ala old SSB days. I think that is all fine. If you get carried away and look for single isolated characters you may be over the line. You can click a blank screen enough times and force any letter to decode standalone.
So while the best remedy is higher power, bigger antenna, better QTH and rarer DX call, you might still be able to better your odds of logging a station by perseverance and skill with your tools.
Good luck with the meteors.
[Despite his modesty, Harry is an excellent operator, and very successful at digging out stations with significantly less ERP than his own. He's done a great service to the VHF Community by presenting some techniques that can help everyone make more contacts using the WSJT software]
Les Rayburn, N1LF
121 Mayfair Park
Maylene, AL 35114
More information about the VHFcontesting