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
transponder are near the commercial TV downlink frequencies.
So it is possible to use cheap LNBs from TV for the
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
So some modifications with other crystals and also with
external reference input were made. But this was not what I
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
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
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
The result can be seen below...
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
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
- modifiy the LNB with the "right" TCXO G0MRF
has tested TCXOs from Conner
Winfield. Regarding to the datasheet
information the series D75F
and capable to handling sub
1-ppm stabilities over a temperature
range from 0-70 degrees
THAT LOOKS GOOD. I ordered some ...but the TCXOs are relative
EXPENSIVE. After they arrived i modified the LNB
AND HERE IS THE RESULT!
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
The drift from midnight and over the daytime is very
stability (14hours) Octagon LNB with Conner Winfield
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
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
This modification maybe does not work with the new
I have only tested the "older
models" with the RDA8565ES
The new TWIN-LNB uses one cyrstal, one PCB, has
internal filters and the RT320M
Maybe anyone can tryout if it works with 25MHz +-
TCXO and give information about.
TWIN LNB "new model" with RT320M (no modification)