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HD cards that can tune above cable channel 125?  

post #1 of 11
Thread Starter 
Do any of the HD PC cards tune QAM above channel 125? I tried the Fusion 5 gold and it only goes to 125. Channel 125 is about 800 MHz. I need one that can tune to 860 MHz.

Dick
post #2 of 11
I don't believe any card uses a tuner clock that supports a frequency above 800.

EDIT: Most tuners used in PC tuner cards can support frequencies up to around 855 MHz, but the cards don't have clocks to support that frequency.
post #3 of 11
Cliff, I don't think that's right. For example, this thread highlights how a driver limitation was overcome and the successful tuning of two channels at 843MHz.

As an edit - I recognize that you qualified the statement with "most", but it is my suspicion that most actually don't have a hardware limitation .... but nonetheless, you could be right
post #4 of 11
Quote:
Originally Posted by CityK
Cliff, I don't think that's right. For example, this thread highlights how a driver limitation was overcome and the successful tuning of two channels at 843MHz.

As an edit - I recognize that you qualified the statement with "most", but it is my suspicion that most actually don't have a hardware limitation .... but nonetheless, you could be right
No mistake. That is a hack that pushes the clock higher than it should be run and can cause timing instability.
post #5 of 11
Thread Starter 
The AverMedia card on Amazon has the following specs:

Technical data

Input frequency range: 54 MHz to 864 MHz
Channel bandwidth: 6 MHz
Channel assignment: US standard
Input impedence: 75 ohms
Modulation modes: 8 VSB/64 QAM/256 QAM

If I believe them, it may tune cable channels up to 864 MHz. Can anyone confirm if that is true?

Dick
post #6 of 11
Quote:
Originally Posted by Dick Kalagher
The AverMedia card on Amazon has the following specs:...If I believe them, it may tune cable channels up to 864 MHz. Can anyone confirm if that is true?
Dick, that spec is a bit misleading. Its a classic case of a manufactuer either not having much to say about the product or there truly not being much to talk about -- which usually results in the specs or feature list being filled with padding. For example, marketing teams for tennis ball manufacturers are probably very tempted to round out their spec sheets with "360 degree circumference" :p

All Aver has done is list what the RF tuner on board the card can do, and as Cliff noted earlier: "Most tuners used in PC tuner cards can support frequencies up to around 855 MHz" .... its just that the cards themselves (being a sum of all its components) do not operate natively operate above 806MHz.

A second fact that is a little damming to the worthwhileness of the spec listed by Aver is the sheer fact that no OTA broadcasts are made above 806MHZ ! (or at least that I'm aware of). It is only some cable providers that are making use of those frequencies (again, as far as I'm aware). And the catcher ? -- the A180 is currently only capable of OTA reception. :p
post #7 of 11
Quote:
Originally Posted by Cliff Watson
No mistake. That is a hack that pushes the clock higher than it should be run and can cause timing instability.
Hi Cliff,

I hear what your saying and tend to agree, but am not uncertain for sure whether there is any negative consequences.

I don't have a data sheet for any of the demodulators used by existing DTV cards, so I had a look at those for some older Philips demodulaors used in analog cards to try to figure out the exact operation characteristics.

Suffice it to say the PLL "clock" uses the frequency of the PC bus (not surprising), but for demodulation purposes a linear muliplier is used (obviously analogous to a cpu's operating frequency). The exact mechanism aludes me as I don't have a deep understanding, nor time to sit down and figure it out, of how the intermediate frequency is interacted upon by the amplifier and the VCO stages...nor what exactly determines the multiplier that is applied to derive the frequency to demodulate.

Given I don't know the specs on the demodulators, their tolerences, or the underlying physical mechanics, I'm hesitant to say whether or not what was done in the Air2PC case would actually result in a frequency that a demodulator shouldn't be driven at, or cause timing instability. Nonetheless, the basis of what you have voiced certainly seems very plausible.

Do you have any specs or deeper understanding that you may be able to provide?

I will link this discussion to the linux-dvb mailing list, for if your assertation is indeed correct, and the "patch" that Tom supplied to Taylor Jacob (who wrote the linux driver for the Nxt200x demodulators) is still part of the driver, it should really be addressed.

TIA
post #8 of 11
I got confirmation from the makers of the Air2PC card that it can tune QAM channels up to 860mhz before I made a patch for the linux driver. They said it was a misprint in their spec sheet and that only for OTA it stopped at 806mhz. So any card that has the nxt2002 demodulator on it should be able to tune QAM channels over 806mhz with the right drivers.
post #9 of 11
CityK,

I may be wrong about this because I was thinking of cable systems that support up to 156 channels (~1000 MHz).

All current consumer tuner IC chips support up to 860 MHz with their internal oscillators and maybe it is simply a matter of the driver supporting channels over 125. I’ll check with the MyHD Chief Engineer when he returns from a trip to see if he will support channels up to 860 MHz.

Sorry for the confusion (I’m old).
post #10 of 11
Quote:
Originally Posted by Cliff Watson
Sorry for the confusion (I’m old).
LOL, No worries Cliff :) It certainly wasn't intentional, and besides, the discussion may lead to a lot of good - specifically:
Quote:
I’ll check with the MyHD Chief Engineer when he returns from a trip to see if he will support channels up to 860 MHz.
I'm sure there will be at least a few MyHD users who would benefit if this can be implemented.
Quote:
I may be wrong about this because I was thinking of cable systems that support up to 156 channels (~1000 MHz)...All current consumer tuner IC chips support up to 860 MHz with their internal oscillators
And now we'll even start seeing PC cards with tuners capable of 1000MHz. For example, the all silicon Microtune 2121, which has already found its way into the newest ATI AIW design.
Quote:
and maybe it is simply a matter of the driver supporting channels over 125
Perhaps. We certainly know the tuner stage of the front ends are up to the task, but whether or not most demodulators can be driven for such frequencies remains unclear. Tom's response about the Nxt2002 is encouraging though, especially given the age of that IC.

Quote:
Originally Posted by tbdombrosky
I got confirmation from the makers of the Air2PC card that it can tune QAM channels up to 860mhz before I made a patch for the linux driver. They said it was a misprint in their spec sheet and that only for OTA it stopped at 806mhz. So any card that has the nxt2002 demodulator on it should be able to tune QAM channels over 806mhz with the right drivers.
Thanks for the quick response Tom. That's good to hear.
post #11 of 11
"Perhaps. We certainly know the tuner stage of the front ends are up to the task, but whether or not most demodulators can be driven for such frequencies remains unclear. Tom's response about the Nxt2002 is encouraging though, especially given the age of that IC."

The internal oscillators of the tuner IC's are specified to support nearly up to 900MHz, but the tuning range also depends on the external components such as a tank circuit.

If the external components are properly selected, the tuning frequency can be increased over the specification taking account of the design margin.
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