I would not put the TCXO on top of the regulator. That is asking for trouble as the regulator temperature variation will be high. Much better to keep the TCXO indoors in a thermally stable environment. Temperature compensation is good, but not perfect.
Mike
My dish is 2.4m and the LNB is a properly modified Octagon Quad, though the MER is often better with unmodified LNBs. It is important to observe the impact of the reference phase noise and select a LO that minimises this. If using a Leo-Bodnar like I am, a change of 1 Hz can make a difference. Aim for minimum phase noise and maximum stability, not absolute accuracy as you can always correct for the latter.
For DATV use, there is no need to modify the LNB LO. However, I also use SSB where it is necessary to for the LO to be much more stable.
Mike
It would be easy to modify the 40mm to 22mm adapter I see there to allow the feed to be 6mm higher and that might be enough. It doesn't have to be exactly centred but you may need to adjust the elevation a little to compensate.
Great - though I would have recommended KiCad. Does design spark also do schematics? I have never seen a BGA heatsink so I looked it up on Google.
Complicated. Here is my solution - but it won't be popular with the analogue operators.
TCXOs....
I have a fair number of microwave directional couplers - 20 dB, 1-2 GHz. I discovered you can use them as an emergency diplexer for the 25MHz if you don't mind losing 20dB of LNB gain. Prevents overloading the spectrum analyser in the above video.
Mike
What about the down converter? Are you using your own and how are you planning to lock the LNB? I have a board for that coming from China.
Ah - so the numbers decrease with increased SNR. They will be dB below the maximum and 57 is 5 dB better than 62. They are not S units. That's more like I expected. I would try a shorter cone but the same final aperture and see if it is the same. Up to 40mm diameter and see if it impacts the S-band pattern. You can't tell by the match, you need to look at the level of your TX over the transponder nose floor. Also the noise floor should increase because you are seeing transponder noise.
Mike
That's right. It doesn't matter which transponder, you still gain with a larger dish, you just gain less and less. At some point the extra gain is not worthwhile so the optimum shifts. With narrow band, it is probably not worth using more than 1.2m.
You could have 50% contribution to the nose on uplink and downlink, this is balanced 50:50 and 3dB down on the best possible. On the NB transponder that's a really small dish, about 60cm or maybe less with a good LNB.
Mike
That is what I did with an Octagon Quad. The 4 connections are 12V, Reference, H and V. There is a mod on the BATC WiKi ( https://wiki.batc.org.uk/Es'hail-2_LNBs_and_Antennaes ) that you can do to remove a resistor that sets permanent H or V on an output. I only modified 1 port to do this.
The port used for the reference is disconnected from the original circuit. The crystal is removed and the 25 MHz fed to one side via a capacitor from the scoket.
The DC in port is unmodified. You could cut the IF track but it is not necessary.
The two IF output ports have had the DC feed inductor cut. This is to avoid DC appearing there but also prevents the 22kHz LO switching so you may not want to do this is you need that facility, put in a DC blocking cap perhaps.
On one If port, it does not matter which, the resistive divider was modified. The chip detects 12V or 18V through this divider and all you need to do is make it think it has 18V when there are only 12V by adjusting a resistor. The only challenge if figuring out which resistor on each type of LNB, but a bit of probing with a multimeter should help.
Mike
Yes I know. But unfortunately not in receive only mode by using a RTL stick. When using a transceiver (FT-100 in my case) SDR console mutes audio to zero. But not to a certain volume. So I prefer my hardware solution. Like in AO10/13 times.
I think SDR Console can mute the RX if it detects a strong signal, but not in your case - I will mention this to Simon. However, a practical solution is to use an relay driven by your PTT to put a resistor in series with your loudspeaker or headphones.
Mike
you really have a 30 m dish?
I do not, but the guys at Goonhilly Earth Station did a test with a 30m telecom dish while they were setting up the QO-100 receiver.
Mike
Your uplink should be circularly polarised so if you are using a linear antenna it's orientation would not matter though 3 dB down.
The phase centre of the feed needs to be at the focus. The phase centre of two vertical antennas will be in the centre of that feed, the phase centre of just one will be where the antenna is, offset to the left or right. This means your dish pointing will be skewed. You can work out how much with simple trigonometry but why does this not impact the horizontal antenna? The same should apply in the vertical plane. I don't know. All I can think of is perhaps your dish is well aligned in azimuth but not well aligned in elevation?
What about putting a single yagi in the middle and seeing what happens as it is rotated?
Mike
Adding a patch to a LNB the feed is no longer a horn but an open waveguide. With a rocket-lense to my open tube nothing changed.
This confuses me a bit. Further research has to be done.
This depends on the f/d of the dish. Assuming a standard offset dish with 0.5 or 0.6 f/d the recket lens should make a difference but will move the focal plane of the feed forward a few cm. You may have to move the feed back a little to adjust for this. With a prime focus dish the f/d is lower and the open waveguide will be better. What is your dish?
See my other post - a larger dish will almost always be better, it is just a matter of how much. The signal to noise ratio is a combination of the uplink and downlink SNR, it can never be greater than the worse SNR. To give you a practical example, 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.
This is very old now from 2007 and perhaps over-simplified as it was for Msc students but http://www.mike-willis.com/Tutorial/PF13.htm
I should address the question directly - for QO100 the law of diminished returns on receive applies. The benefit of a larger dish falls quickly above 1.2m and there is little point going above 3m. This does not apply to TX where a larger dish will always be better - as long as you can aim it accurately.
Mike
If it is 5 S units worse with the cone (-30 dB!) pie cooking remains the best use. I wonder if your post is written incorrectly?
Such a cone will act as a horn at 10 GHz, it will focus the beam to a better match to a longer F/D - this is what the lens does as well. However, it will also move the 10 GHz focus much further forward and this would require correction but then the 2.4 GHz and 10 GHz focii would be too far apart requiring you to optimise for one band or the other.
Silver plating won't make much difference but it does look nice.
Mike
Quick test with G4JNTs Signal-Noise monitoring package - 1W CW TX, SNR 58 dB Hz which suggests an uplink G/T of -11 dB/K. That is much worse than I expected so either my dish is not good or it's not very sensitive. I do recall much better results earlier on before the gain was reduced, but I don't think it could be that bad so perhaps a combination of both. It would be nice to have some other measurement datapoints.
To get a specific SNR with known EIRP tells us what the satellite G/T is. Unfortunately I do not know what the SR bandwidth is in SDR Console but luckily I did some spectrum analyser measurements recently.
The beauty of this is I can go back and do analysis on the data. This tells me the Resolution bandwith and other settings and allows me to measure stuff - the result of which is the PSK beacon is 18 dB above the transponder noise floor in 3 kHz. The beacon is 400 baud BPSK and from observation the majority of it's power lies within 1-1.5 kHz so we may have a correction to make.
However, looking at the data the analyser was set to peak so the noise is peak detected too, and video averaged so it's level is somewhat uncertain. What I do know is it is at least 18 dB, probably 22 dB, possibly more. Too much uncertainty. Send contrary arguments to my server at /dev/null.
If it were 22 dB, plugging this into a link budget gives a G/T of something like -6dB or -5.5 dB. That's not so unreasonable as a global satellite beam is about 22 dBi. However the errors in guessing the beacon EIRP based on my 200mW to equal it and not being quite sure where the noise floor is are too much.
Time to try a measurement I think -
G0MJW we do have a link budget with is in very good agreement with the observed performance. But as you feared, this has too much NDA'ed information in it and for the sake of staying clean, I will not publish any numbers myself (sorry for being paranoid).
However, if anybody else is generating a spreadsheet which can be verified by the QO100 community, there is nothing we can do about...
OK - understood. Not everything in the spreadsheet will be under NDA though. I see the noise floor at ~10dB. Assuming antenna gain of 45 dB and a noise temperature of 400k I have a G/T of 19 dB. PSK Beacon SNR is 31.5 dB. This is according to SDR Console, I don't know if it is right but as long as it is consistent it does not matter.
To equal that SNR in the same bandwidth with a similar signal, I need to transmit about 200mW.
This is where errors start to creep in as I find if I TX at this level I am a lot weaker than some other stations who are apparently sending at the same level as the beacons.
My dish gain on 2.4 GHz is (assuming Willi's simulation is correct) is 32.5 dB so an EIRP of 25.5 dBW is what I need to reach the beacon level. It should be mostly the same for everyone else.
Now we could say at this point job done. To have a sensitivity such that the transponder noise is equal to the antenna noise one needs a dish with 7 dB less gain (not exactly, close enough though) other things being equal. -7 dB equates to 1/5th of the area, about 1.1m. The equal noise is an arbitrary target by the way but a fair one.
There are some improvements to the ground station that could be made, I assumed 50% efficiency and a noise figure of 3 dB and about 120k dish temperature. Realistically, this could be improved to 200k with a lower noise figure and better side-lobes with 70% dish efficiency. That's probably the limit without going to extremes. That would allow another 3 dB and a 75cm dish.
Part 2 after lunch
It's not only the 2m and 23cm bands that are under study...pretty much all spectrum, DC to daylight and negative frequencies too, are within the sights of the mobile community.
