RF Modulator Questions

[Electronic M]

I've only seen through hole lytics in BT agile mods. A they need is the lytics and as long as you get polarity and value correct, and do a decent solder job you won't introduce new problems.

[Tube TV]

I noticed with mine the ripple changes with how the IF in IF out jumper is placed, and where the antenna wire is placed also.
Seems to be beeter also when it warms up.

Agreed though they're all due for some new caps though.

[ARC Tech-109]

How are you verifying the actual carrier frequency of the modulators?

[trinescope]

The "newer" BT modulators have surface mount electrolytics that go bad, and cause all sorts of problems as well. A flashing green status light indicates one or both PLLs out of lock, most likely from bad 10uF SMD caps under one of the shield cans.

[Electronic M]

The nice part about SMD lytics is that if there isn't anything else SMD too close even a hack like me can touch a regular soldering iron to the leads and get them to come loose...I've soldered regular through hole lytics to the pads and fixed VCRs and computer gear with surface mount lytics that way...The phrase crude but effective sums it up.

[Tube TV]

If you're new to soldering the best thing you can do is get a bunch of junk circuit boards and practice on them till you get the hang of things. Removing and installing components on them then move on to something you actually want to use or care about.

[vintage.digi]

Have any of you guys ever used a "leaky" coax as an antenna? I was researching antenna options for UHF broadcasting which brought me to this, which seems like it could perhaps be a great option for my interconnected metal buildings. I haven't tested the UHF transmission of combined channels yet, but I did find this diagram in the manual for my UHF modulator which shows the output connected to an amplifier and antenna: fig 2. http://files.d-tools.com/Visualizati...-1_Manual1.pdf

It actually shows the modulator output running to a splitter which then goes to both wired coax and wireless, but I have no need to do that in my situation. (The UHF broadcasts will be VHS simulcasts)

My mini modulators don't have power supplies built-in, but I think I fixed a lot of the interference by replacing my old MIPS-12 power supply with a new MIPS-12D, and also additionally skipping channel 2 as this channel had more issues on older sets than any others. It's still not 100% perfect, but I have to really be looking to see the issues in most cases, and I feel like they're likely in line with the sorts of issues that were present in TV signals when I was younger.

As for the question, "How are you verifying the actual carrier frequency of the modulators?" Currently I'm not. I'm just learning all of this. How would I verify this? Also, if it was out of calibration, is there anything I could do about it? I don't recall seeing any adjustment pots inside but I didn't look for them when I changed the jumpers.

So far, I've managed to get things pretty functional by just eyeballing. I would like to learn how to set this stuff up properly over time, as I'm able to acquire the needed testing equipment. Right now, I don't have much in the way of testing equipment asides from a multimeter, CRT tester, and a pattern generator.

I also will need to learn how to set an RF amp. Currently I'm setting it to the lowest amplification level that doesn't cause static, and I'm setting the slope to nothing in particular.

[Alex KL-1]

For WiFi (wireless, ~2.5GHz SHF), some leaky cable solution exists: long waveguide resembling a large cable, with spaced holes, but I dunno if this solution is applied to UHF (I never searched about).

[Alex KL-1]

...for subbing PSU caps in these modern equipment, I use the solid polymer series, since these support very high ripple current, higher than most common electros. Guaranteed long live!
Some concern about the low ESR of it interactinc with PSU feedback possibly making instabilities exists, but in practice, I never seen a PSU turning unstable using it, so I personally recommend. And the lower ESR of it helps to lower the PSU ripple.

[Electronic M]

Originally Posted by ARC Tech-109

How are you verifying the actual carrier frequency of the modulators?

I wonder how many of us actually do that...

On my Blonder Tongues if I can get them on a TV tuned to the same channel I take it for granted that they are on frequency.

On some continuously tuned modulators I have I typically take a VCR with manual channel configuration in the menu and with the modulator off or detuned configure the VCR to tune the channel(s) of interest and disable blue screen then I tune the modulator until it comes in properly on the VCR on the desired channel.

The proper way to do it would be to get a GHz capable digital scope, spectrum analyzer, or RF network analyzer and use that (there may be CATV tools that can work, but I'm not familiar with any), but I'm allergic to spending 3-5 figures on test equipment.

It's probably possible to economicly do it with an SDR, but I haven't simultaneously had time and money to go down that interesting rabbit hole.