There is a huge difference in signal quality between Mode A and Mode B on AO-7. I've been working Europe on Mode A days and have found that the audio quality is excellent. I've experimented with higher power levels to see how the transponder performs and have found that it can handle the highest power levels on the uplink without fm'ing, distorting or creating images across the passband. Of course it is harder to hear with severe fading on a horizontal beam antenna, but it is very usable.
This morning there were three French stations on in Mode A. F6FLE was pounding away on CW and loud. But there was no apparent degradation of the other voice stations using the transponder at the same time. Strong CW on Mode B just kills voice readability and strength on other stations. No images were heard, the passband was quiet except for other ham radio transmissions. I have several antennas for 10m. The one I use for Europe is a 5 element beam at 120'. It can see the horizon in all directions and can hear AO-7 when it is below the horizon. For higher elevations I use a single element at about 15 feet. The Mode B transponder never sounds very good. And it seems to be in a power limited situation even when there are no ham radio transmissions in the passband. What you do hear is all kinds of noise and I suspect this noise is the culprit in robbing all of the available power to run the transmitter. The noise moves and is probably being received from ground sources, hence the apparent doppler. User stations sound choppy even when running minimal power. When you run more power, signals FM and images are heard within the passband. The question is what is the source of all the crud that AO-7 is hearing in Mode B? After all, 432 is supposed to be used for weak signal operation and should be very quiet. Are there issues within the satellite that contribute to this? If you were a user of AO-7 back in the 70's, what was Mode B like back then? Of course it had a better power source when the batteries were still functional, but was the signal/audio quality much better? Did it FM and was the audio choppy? We are very fortunate to have AO-7 regardless of the performance issues. It is challenging to work at low elevations but the payoff is worth it. What we would really appreciate here in North America is more activity from Europe on the passes that reach the across the Atlantic. Last week I had a qso with IK8YSS in Mode B, 7554KM. I have seen his callsign in the AO-7 logbook for a long time and finally we had a mutual window with good conditions. LA4FPA/p was on yesterday as promised from JP22. AO-7 might not be the HEO that many wish we had, but it is the highest bird we have right now. Let's use it while we still have it. 73, John K8YSE _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
