I have been working on a low cost RX system
The system is based on:
an Avenger PLL321S-2 LNB
a 64 cm offset dish from Triax
which is mounted on a IOPTRON Gearbox
and then the Funcube dongle.
I have done some measurements on the Avenger LNB
First I tried to find frequency stability, it seems good enough to use it
If needed the temperature of the quartz can be stabilised
Then I tried to find the Noise figure performance by measuring cold sky to hot earth Cs/G.
I am using the Funcube dongle connected to the Avenger LNB and found no difference between Cs/G.
After some testing I found that the Funcube is already in compression just by the wideband noise from the Avenger.
After adding 20 to 30 dB attenuation I could see difference between Cs/G.
I measured on 10368 and on 10750 MHz the noise difference from Cs/G
nF performance off the Avenger within the operational band of the LNB is about 1 dB better
With a noise figure of about 1.8 dB @ 10368 MHz we will lose about 2 dB in S/N compared to an LNA with a nF of 0.8 dB
Using an offset dish with 64 cm doing almost 35 dB gain @ 10368 I should be able to receive DL0SHF in low power mode.
First I would like to measure solar noise to find performance of the overall system, if that looks good I will try to search for DL0SHF
On 23 November 2014 I did make my first measurements with this low cost system.
At first I tried to measure without adding attenuation in front of the Funcube dongle, results were looking very strange and totally useless.
Then I added 20 dB attenuation in front off the Funcube and results were much better.
I also tried to switch off the LNA in the Funcube and then use no 20 dB external attenuator but this was not working, don't quite understand why but it was no good.
So I performed my measurements with Funcube dongle using the normal default settings and a 20 dB attenuator between the Avenger and the Funcube dongle.
I did sun noise measurements and cold sky measurements and my best results are visible in the picture below.
At start my Avenger LNB was positioned in the most backward position off the feed holder.
I tried to optimize the position off the Avenger LNB and found performance best when it was in the most forward position off the feed holder, this gave me an improvement off 0.5 dB in solar noise.
I measured solar noise to cold sky at best at 3.9 dB
Sun noise to cold sky (0.5 dB/div)
I also measured Cs/G with the Avenger mounted in the Offset dish.
The Cs/G value I measured is 3.0 dB
When I turned the elevation from 15 degrees to 90 degrees I find a change in cold sky noise level off about 0.3 dB with minimum noise at 30 degrees elevation
A solar noise off 3.9 dB looks very promising for receiving DL0SHF on low power.
When moon declination is more to the North I will try to receive DL0SHF with this setup.
Interesting webpage of HB9AFO about the Avenger LNB: http://www.hb9afo.ch/articles/pll-lnb/10ghz_pll-lnb.htm
An inside story off the Avenger and if needed a way to improve frequency stability: http://f1chf.free.fr/LNBPLL/inside.pdf
Perhaps I will open up my Avenger and try to optimise the nF performance for
The mechanical setup off my low cost system
I mounted the offset dish to the IOPTRON gearbox dovetail plate using two M5 screws, had to drill holes into the support off the dish
I made a counterweight using two lead plates mounted with two M8 threads. the weight off the counterweight is about 2 kG
At first I did not receive anything and I contacted the first operator of DL0SHF
, Per DK7LJ to ask if the beacon was on, and it was on.
Again I did not find the beacon and did not understand so again contacted Per to get confirmation that the beacon was on high power which it was.
After more checking and testing I tried to turn my polarisation a bit and then I found a weak signal. I found that polarisation was 90 degrees wrong, I do not yet understand why, will need to do some further measurements on the Avenger LNB.
After I turned the polarisation and optimised my dish signal was fine
About 8 dB S/N in 12 Hz bandwidth (2 dB/Div)
After the beacon was switched down to low power I still could see the beacon on
my SDR with acceptable signal
About 3 dB S/N in 12 Hz bandwidth (1dB/Div)
WSJT Decode in low power mode
WSJT decode in high power mode
Some things need to be further tested.
First off all the difference between high and low power from DL0SHF should be much more difference
Second, why is the Avenger LNB 90 degrees wrong in polarisation or what did I do wrong with it
I also want to try to receive DL0SHF when moon is higher now it was at 17 degrees elevation just on the lowest possible elevation off my antenna
Also I will then try to measure moon noise, today this was not possible