Problem tuning frequencyusing Nova S plus

I am having a problem tuning to a couple of particular frequencies
using a Hauppauge Nova S Plus. There are two transponders very close in
frequency and neither of them will give a lock, while other
transponders from the same satellite lock just fine.

The satellite is: Intelsat 10 (IS-10) (68.5E) -

and the transponder I am interested in is: 3864.00 H - Txp: 4 - Beam: C
DVB-S (QPSK) - 19850 3/4 - NID:65535 - TID:1

I can tune to transponders either side of this, but I fail to get a
lock when using dvbtune.

root# dvbtune -f 3864000 -s 19850 -p h -c 3 -cr 3_4

No CA device found, skipping

Using DVB card "Conexant CX24123/CX24109"

Using C-BAND parameters LOF=5150000

tuning DVB-S to Freq: 1286000, Pol:H Srate=19850000, 22kHz tone=off,
LNB: 0

Setting only tone OFF and voltage 18V

DISEQC SETTING SUCCEDED

polling....

Getting frontend event

FE_STATUS:

polling....

Getting frontend event

FE_STATUS: FE_HAS_SIGNAL

polling....

polling....

polling....

---- give up

Setting the debug=1 on the module I get this in dmesg:

CX24123: cx24123_initfe: init frontend

CX24123: cx24123_set_tone: setting tone off

CX24123: cx24123_set_frontend:

CX24123: cx24123_set_inversion: inversion auto

CX24123: cx24123_set_fec: set FEC to auto

CX24123: cx24123_set_symbolrate: srate=19850000, ratio=0x003ed29a,
sample_rate=40444000 sample_gain=1

CX24123: cx24123_pll_tune: frequency=1286000

CX24123: cx24123_pll_writereg: pll writereg called, data=0x00100e3f

CX24123: cx24123_pll_writereg: pll writereg called, data=0x000a0180

CX24123: cx24123_pll_writereg: pll writereg called, data=0x00000201

CX24123: cx24123_pll_writereg: pll writereg called, data=0x001f84f7

CX24123: cx24123_pll_tune: pll tune VCA=1052223, band=513, pll=2065655

CX24123: cx24123_read_ber: BER = 0

CX24123: cx24123_read_signal_strength: Signal strength = 64768

CX24123: cx24123_read_snr: read S/N index = 64135

CX24123: cx24123_read_ber: BER = 0

CX24123: cx24123_read_signal_strength: Signal strength = 64768

CX24123: cx24123_read_snr: read S/N index = 64197

When I tune to a very close adjacent channel I also get a failure:

3863.00 V - Txp: 15 - Beam: C DVB-S
(QPSK) - 20600 3/4 - NID:6144 -
TID:9

which is only 1 MHz different from the transponder I am interested in,
though on a different polarity.

When I tune to an channel some way off I get a lock, for example:

dvbtune -f 3836000 -s 20600 -p v -c 3 -cr 3_4

No CA device found, skipping

Using DVB card "Conexant CX24123/CX24109"

Using C-BAND parameters LOF=5150000

tuning DVB-S to Freq: 1314000, Pol:V Srate=20600000, 22kHz tone=off,
LNB: 0

Setting only tone OFF and voltage 13V

DISEQC SETTING SUCCEDED

polling....

Getting frontend event

FE_STATUS:

polling....

Getting frontend event

FE_STATUS: FE_HAS_SIGNAL

polling....

Getting frontend event

FE_STATUS: FE_HAS_SIGNAL FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI
FE_HAS_SYNC

Event: Frequency: 11064000

SymbolRate: 20600000

FEC_inner: 3

Bit error rate: 0

Signal strength: 62464

SNR: 65252

FE_STATUS: FE_HAS_SIGNAL FE_HAS_LOCK FE_HAS_CARRIER FE_HAS_VITERBI
FE_HAS_SYNC

I was wondering if anyone had come across a similar problem? I am
speculating, but maybe this is interference from an adjacent channel
since other channels with wider spacing always work. Interestingly a
commercial satellite STB can tune to this transponder without errors,
so this does indicate a driver releated buglet.

Are there any cx24123 parameters that could be tweaked to help here, or
maybe this is a tuner problem?

Could anyone provide me with the data sheets for the demod and tuner
for these cards? I would be happy to dig into this a bit deeper.

Regards

Pete

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