An Adventure in Oscillator Theory

[jr_tech]

Originally Posted by VintagePC

Target frequency range is cable 14-83 minus ch5, or 44-500MHz.

But channel 5 is 76-82 mHz, so at some point in tuning, your oscillator will be tuned to the output frequency... there will be a range of channels that will suffer severe interference.

If you add enough "C" across the tuning coils to get the resonant frequency as low a 44 mhz, the tuning range will be greatly reduced.

Are there any cable channels in that range that are NTSC, anyway?

Fun project, but I seriously doubt that it will yield useful results.

jr

[VintagePC]

Originally Posted by jr_tech

But channel 5 is 76-82 mHz, so at some point in tuning, your oscillator will be tuned to the output frequency... there will be a range of channels that will suffer severe interference.

If you add enough "C" across the tuning coils to get the resonant frequency as low a 44 mhz, the tuning range will be greatly reduced.

Are there any cable channels in that range that are NTSC, anyway?

Fun project, but I seriously doubt that it will yield useful results.

jr

Aye, a very valid point. I was doing some experimental calculations to see what would happen when trying things like 2C, 4C, 8C 16C etc... and noticed that at 16C you get a LO of 117 low side, but your high end suffers and is down to 222.

As for interference, that would definitely result in a complex mess to clean up.


Cable and broadcast share frequencies on channel 2-13, then they diverge, except for the high end of cable which overlaps with the low end of broadcast (which is why the converter picks up Ch62-70 cable). http://en.wikipedia.org/wiki/North_A...ble_television has the details.

What's the practicality of inserting a second fixed-frequency LO mixer to simply upshift the incoming cable signal by 350Mhz before mixing with the LO? There'd probably be a detrimental effect on reception but it would boost the channels into rage of the converter... and I do have some more 6AF4s kicking around...

I don't really have any anticipation of this actually working but I figured it would be a neat "let's try and see, just because".