jac1dlists at gmail
Dec 1, 2009, 9:41 AM
Post #4 of 11
Thanks for confirming things Andy, Devin.
Re: cx18: Comparing SNR for OTA channels?
[In reply to]
I am getting 21.5 to 22 on SNR, which seems quite low. This is for OTA
signals. I'm used to 25++ on a cable network. I am quite a distance from
the transmitting tower, and at a low elevation so perhaps it is to be
expected. I'd be curious to hear what others are getting and their relative
distance from the towers if they know it. I'm about 35 miles away.
It seems to be consistent across all three stations, which are all coming
off the same tower as far as I am aware.
Generally the video performance is very good but I get occasional periods of
lost packets and slight pixelation in small areas, which is consistent with
being near the lower end of signal strength and losing a few packets.
At the moment I am using dvbstream to stream the output but I'm finding it
dies with a buffer overflow error after a random period of time. I suspect
this may be related to the signal strength and mangled packets, but I
haven't looked in to it in any detail yet. Is dvbstream normally stable for
long term streaming?
On Tue, Dec 1, 2009 at 3:33 AM, Andy Walls <awalls [at] radix> wrote:
> On Mon, 2009-11-30 at 23:41 -0800, Jeff Campbell wrote:
> > Hello All,
> > I was using the ATSC tuner side of the HVR-1600 over the weekend and I
> > had a hard time determining my signal strength or finding a place
> > where I can get a consistent SNR reading that can be used to compare
> > the relative strength of the various channels I am able to tune. What
> > is the recommended way to determine signal strength and SNR?
> I'm sure Devin has a lot more details than I, but you can look at the
> output of femon. Keep the following in mind:
> 1. The status is coming from the s5h1409 module, the driver module for
> the ATSC/QAM demodulator
> 2. The signal strength is bogus. From the code it looks like a copy of
> the SNR.
> 3. The SNR value will only be valid when there is a lock. Don't count
> on it otherwise.
> 4. Since Steve Toth wrote the driver, I'm assuming the SNR value is in
> 0.1 dB, but I'm not sure.
> That of coure still doesn't give you what your margins are for good,
> bad, and marginal for 8-VSB, QAM-64 and QAM-256. I suppose one can look
> up the theoretical BER vs SNR curves to find out.
> That's actually one status output I would like: SNR margin. The
> absolute values don't mean much to people.
> > -Jeff