On Thu, 2012-10-25 at 16:10 -0400, Aram J. Agajanian wrote:
> On Mon, 22 Oct 2012 13:15:43 -0400
> "Aram J. Agajanian" <agajania@cs.newpaltz.edu> wrote:
>
> >
> > I have several WinTV PVR-150 MCE cards. I am using them under CentOS
> > 6.1 for FM radio receiving and scanning.
> >
> > Some of the PVR-150 MCE cards have the LG TAPE H001F MK3 tuner. With
> > these cards, the ivtv-radio scan (-s) function doesn't pick up many
> > frequencies.
> >
> > Some of the PVR-150 MCE cards have the TCL MFNM05-4 tuner. With these
> > cards, the ivtv-radio scan function picks up many more frequencies.
> >
> > Is there a way to the cards with the LG TAPE H001F MK3 tuner to be as
> > sensitive as the TCL MFNM05-4 tuner?
> >
>
> Today, I tried to scanning for FM radio stations with these cards
> using the latest Fedora 17 kernel (3.6.2-4.fc17). I found that the
> same problem occurs. The cards with the TCL MFNM05-4 tuner model scan
> better than the cards with the LG TAPE H001F MK3 tuner.
AFAIK both the TCL MFNM05-4 and the LG TAPE H001F MK3 are both clones of
the PHILIPS FM1236 MK3. The linux tuner and tuner-simple module treat
them identically.
That's probably wrong, but without detailed engineering data on the
tuner assemblies, it is hard to know the proper mixer-oscillator / IF
demodulator AGC take-over-points (TOPs) to set for best noise
performance.
Your options are:
a) modify the tuner-simple and/or tda9887 module to play with the TOP
setting to see if they even matter and experimentally find optimal
values.
b) modify the tuner-simple module to dynamically set the tuner charge
pump for fast PLL operation when doing a tune and then coming back to
slow PLL operation for low phase noise when tuned. (IIRC, the
tuner-simple module has the change pump fixed at slow PLL operation for
good performance when tuned.)
c) modify ivtv-tune.c to pause for a short while between
VIDIOC_S_FREQUENCY and VIDIOC_G_TUNER when scanning. It really is
probably just a matter of time to get a signal lock declaration is
different between the tuners.
d) modify your RF cabling plant to good performance:
- An FM antenna with some altitude
- A 300 ohm - 75 ohm balun connecting antenna to RG-6 coax
- A high gain, low noise, VHF/FM amplifier covering 88.0 - 108.0 MHz as
close to the antenna as possible. The overall noise figure of the radio
receiving system is dominated by the noise figure of this first
amplifier.
- A coax grounding block to ground the RG-6 coax shield to ground to
reduce EMI and provide lightin protection
- If required, a variable gain ditribution amplifier to prevent the
signal received by the tuner cards being to weak or too strong.
Overdriving tuners degrades their performance by the clipping creating
intermodulation products that show up as noise.
- Proper splitters, cabling, and termination.
http://ivtvdriver.org/index.php/Howto:Improve_signal_quality Options c) & d) are easiest. Options a) and b) probably aren't worth
the effort.
Regards,
Andy
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