Would an old tube UHF to VHF converter work on HDTV?

[wa2ise]

I would think that an old style vacuum tube UHF to VHF TV channel converter should work with over-the-air UHF digital TV channels, feeding it into a DTV set top box or DTV set set to the appropriate low VHF TV channel, channel 5 or 6 if I recall correctly.



However, I don't know how the DTV receiver, set to channel 5 or 6, will tolerate the converter's frequency drift over time. Also, tuning the converter may be tricky in that it takes some time for the DTV to lock onto a decent signal after it sees one.

[vinyldavid]

Just a question, but why would you want to do this?

You should just be able to run an antenna into the converter, and then the RF output to channel 3 on a TV.....

That's what I do.

[wa2ise]

Originally Posted by vinyldavid

Just a question, but why would you want to do this?

No practical purpose, other than the fun of doing it, and to show that an old tube device can pass modern DTV signals.

[vinyldavid]

Originally Posted by wa2ise

No practical purpose, other than the fun of doing it, and to show that an old tube device can pass modern DTV signals.

I like your reasoning!

Go for it, and let us know what happens.

[ChrisW6ATV]

If you let the UHF converter warm up for a while (10-20 minutes or more) and have a known-good, strong digital UHF signal, it may indeed work. Most likely, though, you will need a lot of patience to make it work, and you will have the best chance if you check the calibration/accuracy of the converter's channel display in advance with an analog UHF signal. (In your picture, the converter appears to be tuned to about channel 41, but it may not be accurate.) The reason for the patience is that I doubt digital tuners have any equivalent of "fine tuning", automatic or manual. More likely, the whole DTV system probably assumes and depends on highly-accurate and stable frequencies and tuning in both the transmitters and the receivers. Your experiment will throw an analog/variable element into an otherwise all-digital system. You may have to use the digital tuner's manual-channel-tune function numerous times, tweaking the converter's tuner position a bit each time, to get the box to find the converted signal.

Since you are also a ham, I would compare this to trying to tune PSK31 with a Heathkit HW-101 or similar...

[bgadow]

It hurt my head to think about this! Easy enough to try; I'll have to do it next chance I get. I was just thinking about how my UHF converters (including a Mallory just like yours) are getting ready to go into retirement.

[old_tv_nut]

Most digital receivers can probably tolerate a carrier frequency error of up to +/- 100 kHz or so.

This should be a fun experiment.

I don't know how flat the response is of these old converters, but if happens to have a *very* strong tilt, that could cause problems also. Also, the thought occurs that you should be sure the 'lytics are good so the power supply is stable and not possibly causing AM or FM hum.

[Captain Video]

...in which I can use the vintage tube UHF converter to feed digital TV signals to an also vintage tube type TV set?

Note: here in Brazil, the Digital TV system is the Japanese ( or something like that... is a Brazilian variation of the Japanese system ), not the American system.

[ChrisW6ATV]

Captain Video, I do not understand your question exactly. You can not modify a vintage TV set to receive digital TV signals, except if you hide a digital-to-analog TV tuner/converter inside the old TV by some method. If you have a digital-to-analog TV tuner/converter that has a VHF RF (analog, converted) output and you wish to change that output to a UHF output (which you could then connect into a UHF converter going to your vintage TV), you may be able to change the VHF to UHF with a device used in the USA in the early 1980's. It is called a "block converter". Here is an example on USA Ebay:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=190140097079

[Robert Grant]

Letting the converter "warm up" for a few minutes should get rid of the worst of the drift.

Powerline voltage variation, if you have any in your lines, is another matter.

Tuning technique: keep a broadband receiver handy to tune the local oscillator of the UHF converter's oscillator (usually this is quite strong, and would not meet Part 15 in a modern product).
If using channel 5 input, take the bottom frequency of the actual channel (e.g.: 470.000 for channel 14 +6 for each channel higher) and subtract 76 (tune to 394.000 to tune channel 14). A digital signal should decode shortly after you hear the oscillator on your radio.
For channel 6 input, subtract 82 instead.

Two pitfalls:
(1) UHF converters, in general, are REALLY insensitive, you will need a very strong signal.
(2) Between the output of the UHF converter, and the input of your DTV converter, there is the opportunity for RF interference from the power supply and digital circuits in the DTV converter itself (and whatever other modern consumers products may be in your home) to leak inward, and make reception difficult.

By the way, you do all realize that all converter boxes tune both VHF and UHF DTV signals (virtual as well as actual channels), and obsolete the need for the UHF converter with your VHF set.

Rob

[Jeffhs]

I agree with Rob's statements 100 percent. There is no need for a UHF converter ahead of your old TV to receive DTV if you already have cable, or a DTV over-the-air converter box; in fact, with either of those hookups, the use of a UHF converter is pointless because they won't work with the new signals (see below).

The old UHF converters were made obsolete when the all-channel reception rules became law in 1964. The converters can still be used (for now, anyway) with old sets that do not have factory-installed UHF tuners, such as many of us here on AK have in our collections; however, the converters will be absolutely useless after February 19 next year, when the analog TV stations (including UHF) will go off the air permanently.

I also feel that DTV converters for TVs using standard antennas (but not digital cable boxes, also known as set-top boxes [or simply set-tops], abbreviated STBs) will eventually become obsolete as well, when all television has been digital for a few years and most homes have flat-panel HD(or SD)TVs. It is impossible to purchase a new analog TV with an NTSC tuner today, unless you are lucky enough to find a store that has an overstock of such sets they are trying to sell off at a discount. Even at that, all existing new-in-box (NIB) analog NTSC TVs tuning channels 2-69 must carry a clearly-worded notice, either on a sticker affixed to the CRT or in the instruction manual, or both (or even printed on the shipping carton in bold type which cannot be missed or ignored), to the effect that the set will not work after the digital transition unless it is connected to cable or an over-the-air converter box with an indoor or outdoor antenna.

[Robert Grant]

<<the use of a UHF converter is pointless because they won't work with the new signals>>

(pointless, arguably so - I think the posters on this thread just WANT to see a UHF converter work, out of personal curiosity. The question here is can a UHF converter -pass- a "newer signal" down to a CECB, and it CAN).

<<The old UHF converters were made obsolete when the all-channel reception rules became law in 1964>>.

(oddly, they really came into their own -after- 1964, when independent UHF stations started coming on the air in large cities, startups made possible by the all-channel law, and many people still had pre-1964 sets with only VHF tuners. My own childhood is a case in point, we did not know of UHF until our parents got a RCA CTC-38 in 1969. The 1959 GE M4 became the second set. There was a great degree of tension between us and our parents, who wanted to watch the color tv in the living room, and would tell us to watch the GE upstairs, only we couldn't, because it lacked a UHF tuner. In the seventies, at least before 9 P.M., UHF stations were like the Nickelodeon of the day. To children, the Big Three were like what would now be called a mixture of CNN and Hallmark Channel, except on Friday evening and Saturday morning. A UHF converter would have brought my parents a lot of peace, but they weren't technically inclined to know they existed. I bought a used one with my paper route money in 1979).

<<The converters can still be used (for now, anyway) with old sets that do not have factory-installed UHF tuners, such as many of us here on AK have in our collections; however, the converters will be absolutely useless after February 19 next year, when the analog TV stations (including UHF) will go off the air permanently.>>

(True, except low-power stations, and foreign analog stations for those who live in border areas, but those are almost trivial).


<<It is impossible to purchase a new analog TV with an NTSC tuner today>>

(an -analog-only- tuner, virtually all the new sets have analog tuners as well as digital, for analog cable customers, and since many of the same sets made for the USA market are also sold in Canada and Mexico, where analog tuners will remain vital until 2011 or later)

Rob.

[kbmuri]

My own childhood is the opposite case-in-point. We knew nothing of VHF except for the funky other dial on the TV set that didn't do anything but show snow. Fort Wayne's first TV station appeared in 1953 as UHF channel 33. Channels 15 and 21 followed shortly, 39 in the early 70's and 55 around 1978. Before that, TV wasn't really done here unless you put up a tower and recieved the occasional snowy Toledo or Indy channel on VHF.

So before and after 1964, TVs with only VHF were useless around here and UHF converters were completely common. My brother and I had one in our bedroom in the late '60's and the cool part of it was we put a VHF-only Zenith portable up high on a closet shelf and put the UHF converter next to the bed. My brother chopped up some extension cords and put a heavy-duty toggle switch on the converter to turn the TV off and on, and also wired up a remote speaker into the headboard with its own volume-control pot. A full-function remote control in the days before remote control. Noteworthy achievement for a couple of 8- and 9-year-olds.

"Pointless" is a subjective term. I think all wa2ise wants to do is turn the same knob after DTV that he did before. I'm not aware of any DTV converter boxes out there that have a knob you can turn -- just high-tech infrared remotes. So the look-and-feel of changing channels the "old way" is lost forever, unless us clever geeks think of some way to do it retro. I hope his experiments work out and he is able to enjoy the fun of getting up and walking over to the TV and fiddling with the tuning, just like grampa did. It's what we're all about here.

[Robert Grant]

Very interesting that people in Fort Wayne had VHF-only sets.

I would have assumed that the department and appliance stores in UHF-only markets (e.g. Fort Wayne) would have stocked UHF-capable sets exclusively.

A big problem with UHF in markets that already had VHF was availability. Catalogs from the 1950's and early 1960's show that almost all sets were sold in both VHF-only and all-channel versions (the latter usually $25 - $30 more expensive, not an insignificant figure in those days). Problem was, in a city with VHF stations, someone who wanted an all-channel set may not have been able to buy one locally, with retailers unwilling to stock such sets due to low demand.

Rob

[kbmuri]

Well, we weren't rich by any means. The VHF-only set in our room was probably 15 years old, even then. Most of the TVs in the neighborhood (including our main living-room set) were all-channel sets. I don't know what the appliance stores were selling at the time -- I was more interested in what the toy stores or the candy stores had on their shelves. The VHF-only Zenith "portable" I'm recalling stretched the credibility of "portable" -- a mammoth box of metal with one gorilla-sized VHF knob in front, above the crt. I don't know where it came from, or when, but I bet it started its life in Toledo or Indy and ended up on the curbside trash when somebody moved from there to here in 1960. Or maybe my dad snagged it from a customer who was upgrading after moving to town.

The several (many) uhf converters I remember from the late '60s were running 2nd household sets or lake-cottage sets. Usually small TVs like Admiral 19A11's or Motorola VT-71's, which by 1968 were "junk". I'm sure these TVs trickled into northern Indiana from elsewhere as they aged.

The uhf converter we had in our room was a Blonder-Tongue "99".