Posts by DL9QJ

Dear Ismo,

you need to consider the Doppler shift.

If you are transmitting exactly on the upper limit of the passband and the bird is approaching your QTH, it will not receive your signal correctly (within passband limits) because it is outside the passband for the bird (this might be 7 - 8 kHz on 70 cm). So you need to adjust your TX signal well below the upper limit of the passband (that frequency limit minus Doppler shift) to stay within the passband.

If you are transmitting exactly on the lower passband limit and the bird is approaching, you should be received well inside the passband limits (your TX frequency plus Doppler shift). And you could TX on a frequency that is (a bit) lower than the lower edge of the passband - Doppler will shift it into the passband. But all this valid only if the bird is approaching!

So the passband limits need to be considered from the view of the sat - not your TX frequency!

Of course, vice versa if the bird departs from your QTH (negative Doppler shift). And the same consideration for the re-transmitted signal (downlink).

So it is not important on what frequency you are transmitting (or receiving), important is that the bird will receive your signal within its passband limits. Then it will be re-transmitted on the other frequency band (within its passband limits), and again the frequency on your receiver might read beyond the passband limits.

Does this answer your question/confusion?

73s Oliver DL9QJ

Removing the xtal:

It is even easier if you use a so-called SMD tweezer (like TWZ100, please search the Web - about 60 EUR if you have the soldering station ). Just add some solder to both sides of the xtal, touch both sides of the xtal with the tweezer, wait a few seconds, and you can easily grab off the xtal. No need to use several soldering irons, additional tools or to remove the PCB.

73s Oliver DL9QJ