Posts by PA3FYM

dd9fj Note that when you place a (dielectric) lens on front of the wave guide, the phase point shifts (towards the dish), so you may need to re-tweak the contraption for optimal SNR/sig strenght.

SV1BDS OK, the 'punishment' has to be real hard in conjunction with your airconditioner. When the airconditioner keeps running, or is off, the system behaves nominal? I ask this because now TC is increased very quickly in the beginning, which may result in loosing lock before the OCXO is 'settled' (at least, I experienced that, that's why I checked mod TC.)

Thanks for the addition, I'll try to work that out in some general conditions, perhaps an extra menu-item to deal with discontinuities like your airconditioner ; -)

min TC = 16, max TC = 1024

Yeah, that could also be an idea, to let the TC decrease as a function of the DEMA and/or a more 'sadistic' approach, i.e. 'punish' harder than rewarding. They are now equivalent (>>4) , perhaps the punish part must be twice the reward (from >>4 to >>3)

DEMA value was chosen arbitrarily , although somewhat based on monitoring its value and my ns-offsets with my contraption.

Room for improvement, so if you want to experiment with it, I would greatly appreciate that. After all, it's your airconditioner ;; -)

Well, that reasoning applies after you have a certain magnitude of the transponder noise.

When the tpx noise was around 10 dB more (the first few months) the perceived SNR (with the same dish) was higher.

Imagine the following experiment:

Suppose you have the tpx noise floor with +10 dB over your system noise and the tpx relays a signal which is 3 dB above the tpx noise floor.

Then the overall tpx gain/power (whatever) is reduced with 10 dB so that the tpx noise is equal to your system noise (and the 3 dB signal is still being relayed).

Having the tpx equally strong as your system noise, the whole noise figure (or SNR) degrades by 3 dB (now you have twice as much noise, because the two noise sources are independent, they can be added stochastically) which also makes the 3 dB signal vanish (into the noise).

OK, I have limited TC to max 1024 (also because I couldn't believe that it could be reached, but you reached it anyway : -)

SV1BDS I saw the logs. Again interesting . . . The 'more frequent sampling' trick works to some extend but apparently your airconditioner does 'something' to which the system can't react fast enough. I also see from your time constant (TC) values that your system is (intrinsically) stable. I never had such large TC's with my setup. What is also interesting, is that your DAC value remains ultra stable, also when TC is lowered.

Perhaps you can experiment with the temperature compensation factor (parameter 'c' in the terminal), it's zero (0) by default. Perhaps try to give it a value ? Point is, that with long TC times, it takes a long time before you notice something, so experimening with temp coeff values will be tedious . . .

I am now in the process rewriting some of the c0de because the TIC software will be enriched with an NMEA parser to display locator and QO-100 AZ and EL angles on a LCD display. Just I leave it here for now and come back later on the 'airconditioner' issue ; -)

From the figures you mention I reckon you can't hardly see the tpx noise floor.

A screenshot would be comfortable.

Something like this (where the NB tpx is around 7 - 8 dB above the system noise).

I meant the span of your receiver , not the transponder

HB9SLV Try if you can distinguish the tpx noisefloor and your system noise floor with a wider span (2 MHz or so).

If you can distinguish, how much is it?

And what about the 23cm issue (amateur usage in relation to GNSS) ?

Good, I'll try to dive into the matter in order to solve your airconditioning issue ; -)

It now polls the status during mod TC, that has to be speeded up.

It's not only the 2m band which subject of study, but also the 23cm band. See this document.

Quote

Oh, you mean an even smaller balloon? I haven't even considered that. My guess is that it would be below the measurement noise then, but I'll have a look tomorrow.

Yes, these 'large spirals' are not uncommon, but at marker 1 there is a discontinuity which I suspect will be the 'circular polarization' balloon.

How about marker 1? I think there is your balloon in the vincinity of Z = 1 (normalized) of the Smith Chart. Perhaps you can reduce your span to zoom in?

Then . . . I can('t!) repeat this infinitely ... don't stare yourself blind at these measurements and resulting pictures. A few decades ago (when sex was dirty and the environment clean) having a RL of 10 dB (equals VSWR50 = 2) on the microwave bands was considered 'enough', anything more was 'nice to have'. People having worse RL's are still alive (and making contacts over QO-100)

The 'loss' (with RL = 10 dB) is only 10% of the power, so the remaining power is 90% which, relative to RL = ∞, is 0.46 dB less (!)

Also, related to the difference between linear and circular polarization (theoretically 3 dB), mutilation of the axial ratio will be a fraction of that.

"Deutsche Gruendlichkeit" is not always 'the' solution for a problem ;; -)

Thomas, I have forecasting skills (although no-one believes me, you're not the only one who experiences the proof, others (here in this forum) experienced the same.
Hint: one of these others is from the UK)

; -)

CT2IRJ Follow this time line a little (also look for earlier photo's). Intentionally designed for after a mixer or Pluto.

G8UGD What frequency was the LO carrier en how much dBc lower than the desired signal?

DH2VA Agreed, but I am 'in the flow' or focusing on this parameter only for practical purposes. Fast lock, stability & accuracy (and cheap! : -)

Concerning Saw Tooth Correction, had lots of experience with that while running Stratum 1 ntp-servers, but to go that far ... We only need 1E-10 precision/stability ; -)

Variance / jitter on the PPS (which is an intrinsic issue with GPS ; -) is attempted to deal with by Lars, have to dig into that issue too. Now there is a low pass filter trying to smear out/average this jitter. The system is not punished hard when it misses a PPS.

SV1BDS I saw the data, interesting ... (first read the mail, didn't understand, until you now tell me you switched on the air conditioning, haha : -)

What happens is that the DEMA, the statistical (or some say economical parameter, especially when it's used in stock trading algorithms) parameter to control TC is floating around zero (0) when TC reaches a certain value, in your case 770 seconds.

Because the DEMA didn't exceed max deviation (arbitrary value, chosen by me as intuitive/educated guess) -at the moment when the decision has to be made to increase the TC- the contraption gets rewarded with a longer TC, in your case:

 TC += TC>>4 = TC + (TC>>4) = 770 + 48 = 818

(B.t.w., 770- 818 seconds is a good value, which means 'the flywheel' is running stable)

'Normally', when DEMA drifts away (at least that is MY philosophy/addition/interpretation) in such a matter that it's risking 'flying out of the bend' this is a sign that the contraption cannot remain its lock with the current Time Constant. So, before it looses lock, the TC is lowered until it reaches a moment that the system remains in lock and that the DEMA is in control and you get 'through the bend' with your car ; -)

However, when a 'severe' discontinuity during this process (i.e. while almost flying out of the bend with your car) is involved and you try to press the brakes, but somebody cut the brake hoses (in this case switched on the airco ; -), a crash (or loss of lock) will be inevitable. That is what happened here.

Hmm.. let me think about it (was some time ago I designed this addition), nice mental puzzle ...

Of course, the external (exterior of the OCXO etc) are of importance. When your contraption is not inside a case, the impact of the airconditioner will be larger than when it's inside a case.

A quick and dirty remedy/experiment could be adding Temp-compensation (NTC or LM35 at (iirc) ADC2) and see how it behaves. Anyway, my recommendation is to box your contraption first.

Rgr, then I wait until the postman rings ; -)