Posts by HB9SLV

A known issue with the Pluto is that its transmitting frequence drifts because ot the temperature rise during tramsmission. At 2.4 GHz, the drift can be several Kilohertz.

There are a number of descriptions on the Web, and particularly on this forum, that show how to replace the oscillator of the Pluto with a TCXO. This corrects the issue, but these SMD components are really tiny, so this modification really needs sharp eyes and steady hands!

So I wonder if it could be possible to minimize this frequency drift, using software. After all, SDR console does an excellent job compensating the LNB drift, by using the satellite's beacon as a reference.

As receiver, I don't use the Pluto, I use a separate RTL SDR stick, so the Pluto's receiver does nothing.

Could it be possible to feed a stable reference into the Pluto's receiver, such as a TCXO, OCXO or GPSDO, and have the software compare it with the actual transmit frequency? For this to be done, part of the Pluto's transmitter output signal should also be fed into the receiver, but maybe the parasitic feedthrough between transmitter and receiver should be sufficient at 2.4 GHz.

The final result would probably not be as good as the TCXO solution, but maybe it could somewhat mitigate the problem?

Now, I know that common wisdom says that "if you think you just had a good idea, be aware that there is probably someone who has had it before you. And if it was feasible, then someone has probably already tried it"

That is the reason why I am asking my question on this forum. What do you think?

Hi,

Has someone tried this amp?

It is advertised as a 2-W amp. If this is true, it would be quite convenient to mount the device right at the focus of the dish, because it looks much smaller thant the usual wi-fi booster, and maybe more weather-resistant with its shhrinked-plastic cover.

They claim 11dB Tx gain (and 10dB Rx gain) and require a 3.7-5.5V supply. Input power is +4 to +20dBm.

I suspect they'll run quite warm but it doesn't look too hard to strip off the heatshrink cover and attach a heatsink.

https://fr.aliexpress.com/item…de-452d-b12a-b7bc705c07af

73s

Quote from G0MJW

the SNR on the wideband DATV beacon here is

~10.5 dB with a 2m dish and not very good LNB.

With a 1.2m dish, with 6 dB less gain, it is ~9 dB.

With a 30m dish with 22dB more gain (yes, 22 dB - think about that) it is ~11.5 dB.

Mike

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Then I assume that in the case of DATV, the noise floor of the transponder must not be as easy to see as it is on the NB transponder.

Because if you can clearly see both the level of the beacon AND the level of noise on the screen of your receiver, using a small dish, then using a 30-meter one would have the same effect as running the received signal through a (linear) amplifier. The sihnal/noise ratio would not improve.

This is the very point of this thread. Why should a larger dish improve the signal/noise ratio of a received signal from the Oscar 100 transponder? This signal is broadcasted by the sat with a given s/n ratio, which cannot be improved lest breaching some thermodynamics law.

you really have a 30 m dish?

Maybe the benefit of a better dish illumination was canceled by signal absorption within the lens.

I was planning to carve a lens to be fitted in front of my LNB, to improve efficiency. The material I was planning to use is wax. Candle wax. Wax being a good dielectric, losses should be low, I hoped.

So I melted a few candles into a cylinder slab 2 cm thick. The first thing I measured was the attenuation brought by 2 cm of wax in front of the LNB. I measured 4 dB with SDR console. This is about what I was expecting to gain with a better dish illumination.

Needless to say, I shelved the project.

A better way ( no absorption losses) should be a secondary reflector. There was such a project in a recent DUBUS issue.

I'm glad I came here to ask this question.

I tried asking the same question on the Facebook group and someone answered that he had tried one 60 cm dish, an 80 cm one, a 1 meter and a 1.5 meter dishes and the bigger the dish, the better.

Thanks again!

Vy 73

That is exactly what I thought. But it is always better to have one's beliefs confirmed by more trained people.

Thank you guys!

Vy 73

Quote from DL5CN

@HB9LSV, the signal to noise ratio at the transponder output depends on your uplink power.

Hello Andreas and thanks for your answer.

You are right, of course. What I should have asked is : " what is the signal to noise ratio of the high frequency beacon?"

Because if it is 20 dB at the satellite, as I see it here with my system, there is no hope I can make it better with a larger dish.

But if a station sends a weak signal to the satellite, let's say 100 mW and a 60 cm dish.

The transponder will output it with a small signal/noire ratio. Let's say 5 dB,

Will I be able to decode this better with a larger dish?

/3s

Quote from PA3FYM

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?

Here is what SDR console says about the Noise floor:

On 10.495 GHz: -94 to -97 dBm

On 10.489 GHz: -94 to -96 dBm

On 10.483 GHz: -95 to -97 dBm

The high frequency beacon : -73 to -78 dBm.

I think I got the point. The noise floor I am seeing is the same within or outside of the tpx band. This means that this noise floor that I am seeing is produced by my LNB.

With a larger dish, the noise floor will remain at the same value but the beacon will be stronger.

Does someone know what the s/n ratio is at the output of the transponder? I started thinking about this when I read on this forum that a few months ago, it was decided to lower the noise floor at the output of the transponder to save energy on the sat.

the nb transponder is not 2 MHz wide. And there is actuvity all the time.

You mean 2 KHz wide?

Hi all,

I am currently using a TV sat 80 cm dish, an unmodified LNB and an RTL SDR.

When monitoring the NB transponder in SSB, SDR Console shows a noise floor at about - 90 dBm and the upper beacon some 30 dB above the noise floor.

Is there any point in using a larger dish?

Signals will certainly be stronger, but so will the noise floor too, with the s/n ratio still at 30 dB..

What do you think?

73s