READY for Es'HailSat 2

my goal for this work:
 
It is planned to launch the first geostationary amateur radio satellite after some delay in the beginning of 2018.
Es'Hailsat2 has 2 S-band(uplink) and X-band (downlink) transponders on board. The downlink frequencies of the X-band
transponder are near the commercial TV downlink frequencies. So it is possible to use cheap LNBs from TV for the reception.
In 2013 there were made some observations from radioamateurs that the PLL-LNBs use a simple crystal for the LO and can be
modified for amateur radio use. One of these types is (was - look below) the OCTAGON OTLSO TWIN LNB.
So some modifications with other crystals and also with external reference input were made. But this was not what I want.
I needed an highly stable LNB  for narrowband use  - SSB/CW/digimode and which can be used for normal TV reception without change.
So i decided to try modifiy the LNB with an internal TCXO.

STEP1 - modify the LNB with an TCXO
The LNB has 2 pcbs and 2 LOs with an 27MHz crystal. But is not easy to find an TCXO which can be used. I decided to buy some
FOX924B
which are very small and cheap. They have a 3.3V supply voltage and need only an additional voltage regulator.
But there is enough space on the PCB to build in the additional parts. I modified one LNB with this TCXO and it works
 nice at first sight. But to find out more
about the stability i tuned to one of the ASTRA2 beacon frequencies.
They can be found  at 11.7075, 11.7105 and 11.7115 GHz on V-pol between the TV signals. The LNB needs to set on the
highband (LO 10.6GHz) for this purpose. The signals are strong and easy to find with an connected SDR on the LNB-IF.
For the frequency drift measurement i used the Airspy  and GQRX.
The result can be seen below...

stability of Octagon LNB with FOX924-TCXO


The screenshot shows the center of the beacon which is very stable over time (about 10hours). But it looks that there are some jumps
on the frequency. 
Anybody has an IDEA?
 So i made some more recherche and found more hints on the website of ZS6BTE to G0MRF.
G0MRF has written an article in the OSCAR News in the end of 2015 and he gave me the information,
that the FOX924 TCXO is digitally controlled and the jumps came from the controlling D/A converter.
So this TCXO it not useable for SSB,CW or digimode.

STEP2 - modifiy the LNB with the "right" TCXO
G0MRF has tested TCXOs from Conner Winfield. Regarding to the datasheet information the series D75F is
 analogue controlled and capable to handling sub 1-ppm stabilities over a temperature range from 0-70 degrees celsius.  
THAT LOOKS
GOOD.
I ordered some ...but the TCXOs are relative EXPENSIVE. After they arrived i modified the LNB again.

AND HERE IS THE RESULT!

modified Octagon LNB with Conner Winfield D75F-TCXO


The measured stability on the ASTRA2 beacon frequency over about 14 hours. The LNB was mounted outside in the focus of the dish.
The absolute offset of the LNB-LO is only about 6 kHz for an overall frequency of 11.7GHz .
The x-scale resolution for the drift measurement is  1 kHz on the IF of 1110.506 MHz.
The drift from midnight and over the daytime is very low.

long time stability (14hours) Octagon LNB with Conner Winfield D75F-TCXO


On an other modified LNB (absolute offset is 7kHz)  i had a look on the short time signal quality and the signal noise floor with GQRX.
The overall frequency span is 2kHz. The timespan of waterfall is 3mins.
The center signal is the ASTRA 2 BEACON at 85cm TV DISH with about 55dB over NOISE!


short time stability and signal quality (3minutes) Octagon LNB with Conner Winfield D75F-TCXO


ALL LOOKS NICE UNTIL NOW, I TESTET THE LNB ALSO ON TV RECEPTION.
THIS IS THE BEST LNB I EVER HAD!


ATTENTION TO THE READERS!!
With the beginning of 2017 Octagon changed the design of the TWIN-LNB Model OTLSO.
This modification maybe does not work with the new ones.
I have only tested the "older models" with the RDA8565ES PLL Chip.
The new TWIN-LNB uses one cyrstal, one PCB, has internal filters and the RT320M controller chip.
Maybe anyone can tryout if it works with 25MHz +- TCXO and give information about.

Octagon TWIN LNB "new model" with RT320M (no modification)



If you need more Information write me an email

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