[mythtv-users] No live tv and not recording

Stephen Worthington stephen_agent at jsw.gen.nz
Wed Mar 14 13:17:36 UTC 2018


On Wed, 14 Mar 2018 10:27:12 +0100, you wrote:

>Le mardi 13 mars 2018 23:19:39 CET, vous avez écrit :
>> On 2018-03-13 12:57 PM, Klaus Becker wrote:
>> > Le mercredi 14 mars 2018, 05:05:28 CET Stephen Worthington a écrit :
>> >> On Tue, 13 Mar 2018 16:52:45 +0100, you wrote:
>
>
>Hi,
>
>Finally I found technical details about my antenna on the Optex web site, but 
>for the moment only in french : 
>http://www.groupe-normand.com/Fichiers/Notices/m701260.pdf.
>
>It says:
>
>• Fréquence d’oscillation basse             9750MHz
>• Fréquence d’oscillation Haute           10600MHz
>• Bande Sortie de Fréquence       950 ~ 2150MHz
>
>I understand in terms of mythtv-setup:
>
>• LNB LOF Switch = 950 ~ 2150 Mhz (?)
>• LNB LOF Low = 9750 MHz
>• LNB High = 10666 Mhz
>
>I tried with several "LNB LOF Switch" at about 1500 Mhz, but channel scan will 
>not work.
>
>Mythtv-setup always says 
>Your frequency setting (114000) is out of range. (min/max:925000/2175000).
>
>Also I wonder if I have to choose as LNB-Type:
>
>    * Bandstacked
>    * Legacy (Fixed)
>    * Standard (Voltage)
>    * Universal (Voltage + Tone)
>
>I suppose Universal ? Only this option allows me to set up the 3 LNB values, 
>otherwise 2 fileds are dark and I cannot modify the values.
>
>Sincerely
>
>Klaus

Yes, that is a Universal LNB, with two local oscillators.  So the low
and high frequencies are what you need.  The switch frequency is not
defined by the LNB - it has to take into account the capabilities of
your DVB-S2 cards and the highest and lowest frequencies you want to
receive from your satellites.  The DVB-S2 cards will have a
specification for the frequency range they support.

The way it all works is that the frequency of the satellite
transmitter (TF) gets mixed in the LNB with the local oscillator
frequency (LOF), and that produces signals at frequencies of TF+LOF
and TF-LOF on the aerial cable down from the LNB.  The TF+LOF signal
is a very high frequency that is probably too high to even propagate
well down the aerial cable, and is so high that your DVB-S2 card will
not see it either.  The card may have a filter circuit to block it if
necessary.  The TF-LOF signal is the one the card needs to be able to
receive.  My TBS 6909 DVB-S2 card can receive 950 - 2150 MHz, and most
consumer style DVB-S2 cards will have a very similar frequency range.
So, using those numbers, you need to have TF-LOF in that range, so
using your low LOF frequency of 9750 MHz, the DVB-S2 card will be able
to receive from transmitters in the range 10,700 MHz - 11,900 MHz.
Using your high LOF frequency of 10600 MHz, the card will be able to
receive from transmitters in the range 11,550 MHz - 12,750 MHz.  There
is an overlap in the middle, so transmitters in the range 11,550 MHz -
11,900 MHz are able to be received using either the low LOF or the
high LOF.  So the switch frequency where reception changes from using
the low LOF to the high LOF needs to be set in that overlap range - I
would suggest having it in the middle at say 11,725 MHz.  The switch
frequency is used by mythbackend to decide whether to tell the DVB-S2
card to switch on or off the 22 kHz tone that tells the LNB to switch
to the high LOF.

The full frequency range you will be able to receive from is 10,700
MHz - 12,750 MHz, so I hope that covers everything you want to receive
from your satellites.

Also note that when you are using an LNB, if you are splitting its
signal to send to more than one DVB-S2 tuner, I think you need to use
mythtv-setup to put all the tuners using one LNB in one input group.
That tells mythbackend that it can only use one polarization setting
and one LOF tone signal on all those cards.  Without that, different
cards can try to use horizontal polarisation on one card and vertical
on another, resulting in two different voltages being sent to the LNB
at the same time.  That can cause damage to either the LNB or the
DVB-S2 cards, or both.  And one card might send 22 kHz tone and the
other not, and that second tuner would then not be expecting the high
LOF to be being used and would not receive the signal it was
expecting.  The best way to arrange that sort of setup is to use one
LNB per card, if you have enough.  If you do have to use a splitter,
make sure you use one that has power passthrough only on one output of
the splitter, so that only the card on that output will be able to
control the LNB polarisation by sending it a voltage.  Then make that
tuner higher priority than the others in the group so it will be used
first and will get to set the required polarisation and LOF.  Note
that I have never had to use input groups as here in New Zealand all
the satellite transmitters we use are on the same polarisation, and
out LNBs only have one LOF.  So I could have that wrong.


More information about the mythtv-users mailing list