Is anyone here experimenting with micro-power analog (or even digital) television?
Hi Ken!
Somewhere in the junk pile I have a 915 MHz NTSC
Part 15 TV transmitter and a receiving converter
for the same frequency that outputs into
an analog TV set.
This gear was given to me, and I had high hopes
for it. However, even though it was sort of cool,
the units did not work very well.
The transmitter and receiving converter used
free running RF oscillators, so they drifted.
After a while, the drift would slow down and
almost stop. The range of these units was only
about 50 to 100 feet. Although, somebody with
a good receiving antenna might be able to
capture the signal from farther away.
The biggest problem, by far, was that the audio
and the video could not be tuned in at the
same time on the receiving end. Something
was wrong with the transmitter. You would
either get a good picture with no audio, or
a lousy picture with fair audio. When I actually
used the unit, I transmitted audio separately on the FM band
instead.
I actually used this set-up a couple of years ago
to help calibrate my OTA (Off The Air) HDTV receiving
converter. It was pretty amusing.
This HDTV receiving antenna was in the attic. That
went down a line of coax into our bedroom. Then I
took the video output from the back of the bedroom TV/VCR
and plugged it into the 915 MHz TV transmitter.
Upstairs in the attic, I had another TV, which was hooked
to the 915 MHz receiving converter. So I could move the
HDTV receiving antenna around and watch what was
being received down in the bedroom. This was fun for
a while. Then when I had figured out how to get
enough OTA HTDV channels, I took the 915 MHz relay
out and through it back in the junk pile.
So that's my experience with Part 15 915 MHz TV transmission.
One person on this board is lucky enough to own a channel 14
transmitter that was marketed by some company 20 or 30
years ago. He hasn't used it for years, but it is a cool
keepsake. It's very low power, but still - it isn't permitted.
Ramsey Electronics had a TV transmitter kit that operated
from channels 2 - 6 (analog.) I saw a demonstration of
one of these on YouTube. I barely got from one room to
another. And again, Part 15 regs did not permit it's use.
Even if we were allowed some low power for HDTV experiments,
say 10 milliwatts or something; it would go nowhere.
I think that some Part 15 stations have video studio cams on
the net though. That's pretty cool. I know nothing about
computer wireless technology, but maybe somebody could
rig up something there for video.
Best Wishes to you, Ken!
Bruce, MICRO1690/1700
I have a TV Genie, from back around 1970, designed to send on channel 14, and before I dug into the rules and realized I cannot properly use it except as a paper weight, here's what I did a few years ago.
When DVD-Video took over, I still wanted to play a few VHS tapes onto the big screen TV, but this required draping cables right across the walking path, not a safe thing to do.
So I sent the VHS tape nine-feet over to the TV, and the picture was razor sharp, but the audio was dull. I found the builder had neglected to install a pre-emphasis circuit and so I set up a project.
Wired to an A-B switch, I was experimentally able to hear the direct VHS audio on the A-circuit, and the B-circuit came from the TV audio output, so that changes to the transmitter audio could be compared to the A-circuit. Ultimately I got the exact match using a resistor and capacitor, which is all that a pre-emphasis circuit is.
If channel 14 ever opens up again for part 15 TV I am ready to start.
Just to satisfy curiosity, I applied video to the "audio" input of an old signal generator. The generator was able to produce an RF signal on TV channel 2. The generator audio input was for AM modulating the signal generator.
Since video is a type of AM signal (VSB) I thought what the heck.
I actually got "some" picture. It was real soft as the bandpass of the audio modulator doesn't pass much of the 4.5 mHz video but, you could see an image.
In the 1990s while our video production business was alive, we wired the house with a closed-circuit cable, fed at one point by a channel 3 modulated output from a VHS tuner. This enabled watching TV anywhere in the house on several TV sets hooked to the cable and tuned to channel 3.
We purchased two surplus video/audio modulators, the kind used at cable company head-ends, and had video production feeds on channels 7 and 13, and we also used the channel 14 Genie plugged into the cable, which was legal.
The two pro-modulators had a variable output up to 10-Watts, way too much for the cable, so we rolled the powers back to a safe line level.
Meanwhile, a buddy used a modulator to send movies to his private-gate neighborhood every weekend. He never got "discovered" by authorities.
It seems to me that it could be very possible to create a lptv station in the 902-928Mhz portion of the band.
Cable TV channel allocations will allow normal Receivers to pick it up.
In the "jumboBand"
143 907.25 to 911.75
144 913.25 to 917.75
145 919.25 to 923.75
source ( http://en.wikipedia.org/wiki/North_American_cable_television_frequencies )
In fact it should be possible and quite practical to Get a DVB modulator putting out 16-QAM or something to go full digital on a modern receiver.
The trick here being the receive station would need a good high gain antenna maybe a pre-amp and a short run of high quality coax. With your transmitter at height @1 Watt and some gain antenna 15+ miles could be achieved.
Current Wireless Internet equipment on that frequency can shoot out over 100miles although its FSK not 16-QAM
And the best part here seems to be that it should be legal under the part 15 ISM rules.
Kent
That TV project is more professional looking then some regular TV stations I've seen.
And the website is so perfect it may be the best one ever seen.
Thanks for sharing.
you know this is something I've been wanting to do for awhile now.
The idea of Part 15 TV fascinates me.
I believe the station shown is not Part 15, but Amateur TV ... you need an a Amateur License, can't be used commercially, can't advertise ... don't know about educational stuff ... maybe a a variance?
Part 15 would be the short range microwave wireless units you would use for watching TV in other rooms not hooked up via cable. The trip into this would be to see how far you can go legally. I believe if you want an audience outside, you'd have to provide a down-conveter or separate microwave receiver for each TV receiver.
look up D-ATV or digital amateur television on google and it will yeild much info on digital tv broadcasting under mostly part 97 but no reason it cant be adapted to part 15.
also
add me on facebook facebook dot com / robert dot chrysafis i have pics of my radio gear links to different info and some various projects.
mention your p15us user name and some technical info related to part 15 am/fm/tv/or microwave in a message so i know you are not a spammer.
Just as a test, I hooked up one of the amplified tv antenna's to the output of a vcr and hit the play button to see if I could get the signal a tv and it worked. I stuck the antenna in a window on the second floor facing out the back of the house took a battery operated tv outside and was still able to get the signal (roughly about 100 feet or so).
wcbo of oldies 1023 fame experimented with something similar many years ago using a vcr, amp and yagi on roof. forget what the results were, but i think it was pretty impressive. it was either wcbo or another friend of mine, was told of this many years ago but cant remember who told me.
That WA6RZW digital TV operation is absolutely
amazing!
By the way, when I was a tech at the University of
Hartford in the late 1980s, we had a professional
channel 11 NTSC TV modulator that took programing from a
satellite receiver to a TV in another building through
a dedicated permanent cable.
Somewhere along the line, we were checking it, and
found that with a wire antenna plugged into the back
(random length, not cut to the channel) it went 50
or 100 feet in the building. That was cool.
I still like fooling around with my Part 15- 915 MHz
TV transmitter. I drifts and you can't get the sound
and picture at the same time, but it's still fun.
Bruce, Dog Radio Studio 2
I think it's pretty quite cool to broadcast on LPTV. Sure, most FCC-licensed LPTV stations play mostly kids programming (probably because of PBS's best wishes to it's fondly kids television, which is actually used to fit the E/I requirements), but there are also several commercial-LPTV stations, like KPVM-LP in Pahrump. Anyone know how much power and transmitter height I should use? Just saying.