Posts by G0MJW

Quote from pe1hzg

I opened it up and voided the warranty on mine, and this is what I found:

It seems this is an RDA5815. It is possible to find datasheets for it, and the specs says it goes as low as 230 MHz (!) but the datasheets i found do not include programming info.

I'm still struggling to rebuild OpenATV from source (before I can attempt to make changes) but I thought this would be of interest.

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That's useful. I see a 27 MHz TCXO there too which could be useful - sniff it's output and send it back along the coax to the LNB.... there is info on the web about this tuner, register settings etc. Minimum RX bandwidth is 4 MHz so it might not be good for lower bandwidths and that explains why it selects any signal on the transponder with the right symbol rate.

Quote from F4HGU

dd9fj how did you attache the Rocket lens (Venton) to the potty antenna? What kind of glue? On my side diameters are closed but different and it doesn't fit well. I need to stick the internal part of the rocket into the cupper tube... That rocket is made of 2 different parts, is it important to have those tow parts totally nested into each others? Thanks.

I used a small bit of electrical tape to hold it in position.

Mike

Here are some test dimensions for 2.25/8.4 GHz.

Only slightly - see the posting in this forum from June. Its 16mm high. It can be retrofitted but the best result also moves the feedpoint a little on a slightly smaller patch and that's not so easy to do after it has been built.

Mike

Computer analysis of dual band dish feed (G0MJW, PA3FYM, M0EYT). Part 2 –S Band

Quote from R1CAU

Colleagues, with all due respect to you, I want to remind you that you are most likely limited to this forum.

Most non-Europeans and, moreover, non-German-speaking radio amateurs do not even know about the Amsat forum, about us, and that we are concerned about the interference here.

They don't know about the webchats either. It beats me how anyone who doesn't understand German or English get's their information. It must be difficult.

Perhaps we need to provide the webchats in Italian, Spanish, Russian, French, Arabic etc etc. So, a question. Is it possible to design a char with automatic google translation so you set whatever language to want to chat in and a seemless translation occurs? There will be some amusing "Out of Sight, Out of Mind" / "Invisible Maniac" events I am sure, but it might get the non-English speaking community to join the discussions.

If anyone is interested, I have been adapting the antenna in two ways, firstly to add a "pie tin" choke ring as suggested by Willi HB9PZK to improve the radiation pattern and secondly a 2.2/8.4 GHz version that might be useful for detecting deep space satellites. This is a rather specialist application, trying to see if you can detect a satellite 100s of millions of km away. Easy with a 35m or 70m dish, not so easy from your back garden.

The choke ring mainly makes a difference to the 2.4 GHz sidelobes. This is not significant enough benefit for QO100. It won't make the signals into the transponder much stronger; it would reduce interference to adjacent satellites, but there are none; it will improve the performance on 2.4 GHz receive, but QO100 systems do not receive on 2.4 GHz. Conversely, the 2.2/8.4GHz feed is only for receive so it's worth adding this.

The Twitter thread is here https://twitter.com/TheRealMike/status/1177286413685014528

So the conclusion is the isolator is usable. What is below the label? Could there be any adjustment?

Quote from pe1hzg

Do we know for certain that the hardware of the SF8008 sat receiver does not tune below 950 MHz and this isn't a software limitation?

The SF8008 also runs OpenATV. I have tried (but so far: failed) to build my own image from source code - once I have that working I can see if there is a software limit that can be bypassed.

Did anyone open the tuner module? Do we know what silicon is used there, and if perhaps the silicon can be coerced to work on lower frequencies?

We know it can't tune out of band as delivered, with the software available but we don't know if the tuner can tune out of band. It probably can, given the right firmware and support components, but with no information, we can't know for certain how much it can be pushed, if at all. I looked inside and there is nothing to see unless one opens up the tuner can. It might be worth sniffing the control lines, or perhaps better buy a minitiouner.

Mike

Ideally perhaps striving for a global Geo Satellite transponder - and before anyone says that's not possible, it is with a network of 3 satellites and inter-satellite links.

Mike

Indeed - but I do not agree with not naming and shaming, but only where there is proof. The individuals should be identified and subjected to whatever due process applies in their country.

Its funny how demand and supply resulted in higher prices for these things. I suppose it is a reflection of the tremendous success of QO-100 and the receiver designs based on these cheap PLL LNBs. There is someone asking 68Euro for one, it might just be a decimal place error but I suspect not. Glad I got my ordering in early.

Mike

Hi David

I don't know as I have not looked but I doubt it. A PLL Ventron Red Rocket might be hard to get hold of and the one I ordered turned out to be a DRO anyway, but other DRO ones are still available. E.g the "Venton Rocket Twin LNB EXL-T 0.1dB Full HD 3D Ready" is £11.89 on Amazon this morning.

Mike

Quote from DD4YR

Position of the moon at 5:30 UTC today:

Thanks - this was behind my comment knowing it was an EME weekend and the interference was fairly short could it have been an EME signal that happened to align with the satellite. Someone with the data and more patience than me could work this out and even geolocate to some extent. We must remember we do not have exclusive access to 2.4 GHz and we should not deploy systems that are not tolerant of these other users.

2400-2402 is the narrow band segment in countries that do not have access to 2320/2304. Therefore it is quite possible and legitimate for someone to be operating in 2400.05-2400.300. That's presumably why this band was chosen as QO-100 uplink as many have access and there is an amateur satellite allocation. Many of the countries that do use 2400-2402 are not in the footprint but on an EME weekend there is a strong possibility stations that are will be using these frequencies trying to contact others. I note the moon was up in asia at the time, EU-Japan EME?

Mike

Unfortunately there are idiots about and ones who like to cause trouble. How about reducing the gain again or making the AGC stronger to make such activities more difficult?

And just a thought, where was the moon?

DD0KP this is the problem but there is no information on where to start without the source code so I don't think it will happen. We saw the classic case of someone being strung along earlier by the manufacturer. They always say yes, in the future but the future never comes. It does work fairly well and the chipset can do it, so my earlier suggestion about tuning a fixed frequency and then adjusting the LNB LO is a good one. It would even be possible to put a narrow filter in there to greatly improve the performance with respect to not locking onto adjacent signals. The reasl fix might be possibly in software, but not if we do not have the code.

Mike

I don't know, you will have to use google to find out for your LNB. Most of us just open them up and work out how to do it. If you can't do that intuitively, this might not be a task you should take on, rather get someone who has some experience to do it while you watch. That way you learn, which is the point after all.

Whatever Dream does is irrelevant. The tuner in the SF8008 is different - but in that case why not use this USB RX?

Now - has anyone found some reliable firmware for the SF8008? Good hardware is frequently let down by unreliable crash prone not properly tested firmware and the SF8008 is no exception to this.

Mike

Nice progress. I could have helped you with the 40mm adapter. I did the same as you but in aluminium. However, the recommended POTY lens is one taken from a rocket LNB and they usually come with a 40-20mm adapter as well. Unfortunately, people are reluctant to keep the lens and throw out the LNB, even though it cost under €10.

Mike

We did a bulk buy of isolators for Jim's PA project. They are probably a drop in replacement. I would recommend you measure it on that VNA you have your eyes on.

Quote from DD0KP

In the manual it is written that you can improve from 40W to arround 50W by obmitting the input and output isolators. This is written on page 5 and the pictures are on page 6. 20W is written is the performance without changes to the PA. Maybe you should try to measure your result on an unmodified one, to get a good comparison of your changes.

That sounds like a really foolish thing to do. The isolators are there for a reason. Don't remove them unless they don't work. Re-tune or replace them perhaps if possible, or compensate for the miss-match.

Mike

Quote from M1CTK

No it does not do offsets. Unlikely perhaps. Yes you do need to modify the PLL, not because of stability but because the tuner will not work below 950 MHz. Therein lies your solution to offsets. Lock the PLL LNB with a variable reference and use that to compensate of the lack of offset tuning in the RX. I.e. The signal always appears at (say) 1 GHz as far as the RX is concerned.

Mike