The Fast-Scan TV Chronicles: The Continuation (2022-11-24)
The progress
Two days ago, my dad talked with the ATN-TV guys through their Whereby net/roundtable.
They were very helpful and gave him some tips on the equipment and how to set it up, alongside confirming that the repeater on Mount Potosi is still active.
They also talked about the repeater's input and output frequencies. Turns out, the repeater might have a different output frequency than what's listed on the website.
But at the very least, it's less complicated than we first thought.
The downconverters
During the meeting, my dad shared a picture of two downconverters that we bought from eBay that hadn't yet arrived.
They were impressed that we managed to find them, given that they were "antiques" and supposedly working.
They're TVC-12G models and were made by P.C. Electronics in 1989.
Unfortunately, yesterday when we had received them, they didn't work.
Here is what one of them looks like. Our specific models are made to downconvert 1.2 GHz, but they were modified to take an input of 1.8-2.0 GHz.
The downconverters are powered by 12V DC, and they have a 100 Ohm antenna input and a 75 Ohm TV output. One of them has a BNC connector for power(?) and the other has a 3.5mm jack. (the kind you'd find on a headphone jack)
We found out that they were modified by the previous owner before my dad bought them, given that they had a label with input and output frequencies that were out of range.
Though I believe that it's possible to re-modify at least one of them to work with the repeater's input frequencies once again. So, we took them apart.
This specific photo shows the inside of the downconverter with a BNC connector for power. The other one has a 3.5mm jack, but are otherwise identical aside from a few potentiometer values.
I labelled the potentiometers with colors and marked down some of their values:
The potentiometers are labeled as follows:
TVC12G W/BNC 12V DC:
Red: 98.9 Ω
Yellow: 0.2 Ω
Blue: 97.6 Ω
Green: 10.06 KΩ (468.3 Ω on other point)
Purple: 0.2 Ω
TVC12G W/3.5mm 12V DC:
Red: 106.6 Ω
Yellow: N/A (didn't check)
Blue: 99.2 Ω
Green: 10.06 KΩ (471.98 Ω on other point)
Purple: N/A (didn't check)
The hookups
My dad hooked up each downconverter to their appropriate power source, antenna, and of course the CRT TV from before.
We were looking to see if the downconverters worked at all, but we couldn't find a signal on the TV, although it did flash a few times and caused some interference on channels 53 and 54.
The correct channel output frequency should be channel 7 or 8 (175.25 or 181.25 MHz video carrier), but we couldn't find anything.
After learning that channels 53 and 54 seemed to be affected by the downconverters, we hooked up the downconverters to an ICOM reciever (of which I don't know the model number) to view the output frequencies.
Turns out that a lot of frequencies were affected, we even managed to find airplane signals on lower frequencies, proving that it is downconverting.
We couldn't find the manual online, by the looks of it only HAM TV only provides them and you need to be a licensed amateur radio operator to get one.
Therefore, I personally can't email them, but my dad can. I'll make a new page with regards to that when possible.
The current state
We're still trying to figure out how to get the downconverters to work, but we're not giving up.
Two days from now, we'd receive a handheld TV scanner that we ordered from eBay, so we'll see if that works.
Come December, we'll have a transmitter to get to Mount Potosi and try to get the repeater to work.
More progress will be shared over time, thank you for reading.