Posts by pe1chl

A calculator is nice to pre-calculate the elevation in case you don't have experience with local TV sats at about the same position, to know what kind of angle (and thus obstacle clearance) you can expect.

However in my experience it is kind of useless for pointing the antenna, because the inaccuracy you get from not knowing the exact direction of south and not easily measuring the pointing direction of an offset dish is far larger than the pointing accuracy required.

So in practice it is easiest to use a TV transponder and a settopbox... and then just slowly pan around the expected direction until you find the signal, then optimize on it. A "satfinder" (a beeper that indicates the overall received signal strength) can also be helpful to find the satellite belt and then pan along it.

In Europe you can always start from a strong transponder on the Astra3 system (23.5 east) and once you have found that turn east finding the next satellite. In Northwest Europe Astra2 (28.2 east) can be used the same way.

In the past it all was far easier with analog TV than now with digital.

Quote from kleiner Peter

What we need is a slim LNB (picture 3) with a PLL (and TCXO, OCXO or an external referenz). But until now I could not find such an LNB.

It looks like the technology for LNBs has changed. I ordered a couple of PLL LNBs in China and received a box that was not even mentioning PLL on it. I mailed back the sender that I got an ordinary LNB while the website said "PLL" and the reply was that it really was PLL. I opened one and he is right, it has a 25 MHz crystal and no DRO.

So maybe I try to order some slim LNBs and see if they happen to be PLL as well. It could well be that the cost for manufacturing a PLL LNB is now below a DRO type and they just silently switched over. My LNBs were only 7 euro each...

Do you think it would be feasible to construct a 13cm feed that would fit around a standard TV LNB? I will use my TV dish with a PLL LNB for receive (it is mounted on a H-to-H motor) and I currently have an LNB that has (with the plastic removed) a neck of 20mm and a horn of 50mm diameter. That could be a bit large to accomodate your 13cm feed, isn't it? Another difficulty is that the horn cannot be removed so it will be tricky to get the 13cm feed fitted around the neck.

That is great news! I wish you good luck with the launch and commissioning!

And let's remember - no transmissions from amateurs until the transponder has been officially released.

Remco,

Please stop taking this discussion into "personal" affairs and as "framing/bashing/judging".

It does not surprise me that you do it, after all it was you that started that row long ago, but I will not discuss such matters here. Nor will I discuss other remarks you have made about your plans.

My question to the builders is just about the preference and operating practices to be used on the satellite, no matter by whom, and the reply from Peter and many others has been clear. It is only to serve as a guideline for anyone who is designing a satellite station or copying another design, and has to make decisions about simplex or duplex operation, not as a personal attack to anyone.

Rob

Quote from DB2OS

Perhaps someone will write an SDR code which will automatically track the beacon while receiving other signals

That is a great idea, it would enable receive using a standard PLL LNB without external GPS reference, which normally is a little too unstable for SSB (and much too unstable for digital modes). When you could point at the beacon and tell the software "keep this at fixed frequency" and then tune around the passband relative to that, I think the free running PLL LNB would be good enough and the mod to feed up 25 or 27 MHz from a GPSDO would not be required.

Quote from Remco

Once the power of the ground station is adjusted
properly (i.e. below level of the LEILA2-jammer)
there is no need for monitoring your uplink signal constantly.

That does not work, because the transponder has AGC (at least all earlier transponders did, I presume this one will have it as well) so the downlink signal for a given uplink output level will vary depending on the other activity on the transponder.

When you have adjusted your power at a busy time, you will cause too strong downlink signal (and LEILA2 warnings) when it is quiet.

Quote from g7iii

Just as aside, a LNB+RTL dongle+ Your chosen SDR software should suffice for the downlink, even providing a nice waterfall so you can _see_ as well as hear that you are no stronger than the beacon, and not transmitting over others.

This would then let you use a single single-band trx just as an uplink.

That is the solution I plan to use. I have a receiver ready with an SDRPlay RSP1a (can easily be swapped for an RTL dongle) and I also have an old ICOM IC-R7100 that I could use. Then an FT-817 with uplink transverter can be used and I have full duplex capability (and waterfall monitoring).

As far as I understand the idea is that a simpler transverter and simpler overall station (using a single single-band trx) can be used when this simplex operation is used, and the opinion of the designer is that full duplex is unusable anyway due to the delay in hearing one's own transmission back.

However, I agree with the others that full duplex really is required. Even when there is no doppler and everything is GPS-stabilized (so the tuning could be calibrated perfectly), the issue of power limitation and monitoring remains.

Quote from Remco

Yes, the setup is designed as 'simplex'.

Solutions that allow only Simplex operation should not be used on the satellite.

See this thread: Simplex operation

What is the "official" position w.r.t. solutions that provide only simplex operation where the operator cannot listen to his own signal when transmitting?

In my experience with older high-orbit satellites it is really required to be able to listen back while talking, even when it can cause annoying problems due to the path delay (stuttering or slow talking), so when doing anything but calling one would turn down the volume on the receive a bit while talking.

However, with equipment that is inherently unable to receive while transmitting, it will be very difficult to judge if the signal is above the beacon, if the LEILA2 system is acting on it, and (when the station is not perfectly calibrated) if one is transmitting over someone else.

I think it would be recommendable to always have the capability to receive while transmitting in the transverter design ("full duplex" operation), and maybe this should be stated in the operating recommendations?

I understand the attraction of having a simplex transverter that could e.g. be used with a single FT-817 to form a portable station, but IMHO it will be very limiting to have no possibility to monitor one's own signal.