Signal Quality!

  • Morning All,


    This isn't a rant but...


    One of the principles of AR licensing is the point of using it for technical self development, be it of skills, hardware, software, RF tech etc. We have been given access to a prize resource aboard a commercial comsat with the two transponders (nb/wb).


    IMHO we should be setting excellent examples of signal quality / purity, and of excellent operating practices. To see what I mean, have a look at some of the signals from Saturday last weekend;



    If you take the standard SSB as 3KHz bandwidth, or even Hi-Fi SSB at 4KHz you can easily see that there are some nasty signals, most likely caused by over-driving transverters, excessive use of compression, far too much mike gain etc. Some of the signals might be comparable to 'Zetagi 27MHz' equipment but we should be doing better than this by monitoring our own TX signals and ensuring they are clean and presentable before connecting our transmit equipment to an antenna; it is clear that ops have and do use the transponder as 'free test equipment'. Certainly in the UK one of the licensing stipulations is that you have equipment to receive on the frequency you transmit on, so it is very easy to monitor your own TX signal for quality / purity etc.


    I did stop using my FT897 noise generator after being horrified at the atrocious signal quality / PLL noise / broadband PA noise being emitted on transmit, it gave me sleepless nights so its been fixed through replacement.


    Is the behaviour possible to modify, probably not, but poor signals being excreted from badly set up ground stations might eventually cause issues for the satellite operator, who after all has a commercial platform to concentrate on.


    We can do better!


    regards,


    Paul M0EYT.

  • Absolutely. If operators can not generate a clean signal or even worse do not understand they need to they should not be permitted to transmit. The lowering of technical requirements for a license can not extend to reduced spectral purity. Firstly, as a community we need to let people with poor signal quality know and help them to fix it. Secondly, persistent abusers, the sort that tune up and down while transmitting to find their signal, regardless of what interference they cause, those that use excessive power and those otherwise behave disruptively need to be firmly dealt with through the licensing process.


    Mike

  • Hi Johannes


    Unfortunately these sort of people do tremendous reputational harm to the hobby. Usually when someone takes a stance like you describe above it is due to their lacking technical abilities or resources to fix the problem. They have possibly spent a lot of money and are in self-denial that all is not right. They often reject criticism, especially where they know deep down that it's true. There is little we can do about such attitudes other than offer to help them fix it.


    Mike

  • Absolutly agreed...


    Of all leisure activities, only licensed radio amateurs have the valuable privilege of experimental use of frequencies.


    In addition to its rights to use frequency bands, the amateur radio service also has the privilege and obligation (for "self regulation") to independently design the intended use of the allocated areas with radio applications (operating modes and band plans). This also includes the coordination of radio operation facilities such as beacons, relays and satellites.


    AMSAT is indeed not in a position to play "Police", we can only give recommendations and advice.

    However, every radio amateur should be encouraged to help and advice others lacking technical experience. This should indeed be done in a friendly manner, not as a sheriff. Some ignorant's may not like it, but than stop giving them nice 59 reports.. there is always a hope for a learning curve ;-)

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG

  • I agree with all of the comments made so far.


    I think that the main problem is that there are some people that are very conscious about the importance of signal quality, but there are many others in the don't know / don't care category. Examples of "don't know" include not having appropriate equipment to monitor their own transmissions, not having technical knowledge to look for or correct problems (some may not be so obvious). Examples of "don't care" include not realizing that QO-100 is a huge asset that we are extremely lucky to have and what we do with it is quite serious, as it gives the world an impression of what we care for as Amateurs, and also being too lazy to do a couple calculations for the uplink frequency and tuning with a TX signal across all the band instead.


    The problem is not specific of QO-100. I think that it just makes it clearly visible in a worldwide scale. But I think that there are other aspects of Amateur radio where the problem is worse. For instance, I once did a study about IMD in the EAPSK63 contest, and the results were rather bad (something like 11th harmonics at only -10dBc with some of the stations). The contest organizers did nothing about it.


    To try to improve this situation, I think that all of us concerned about the importance of signal quality should try to create a culture on the bands. I should apply these recommendations first to myself, but I'm going to list the aloud here: when you see someone on the bands doing something inappropriate, just tell them and stress why it is important. Examples of this include when you are calling CQ and see someone tune across trying to reach your frequency, working a station with visible spurs, too wide of a modulation, signal stronger than the beacon, splatter, also low audio quality because of compression (even if the signal is fine spectrally). Just tell them politely but stressing the importance.


    Probably there are some people who will be offended by the comment and try to argue back, but I bet that many other will be either surprised or interested and will like to care or learn more. Several times I've had a station with some of these problems call me and I haven't told them anything. Now I realize that by not telling them anything I am just contributing to the problem. Also, if you see a station with a really horrible signal, just call them and tell them.