[HomeBrew] Re: Wireless CATV

[Steve Uhrig]

On 3 Aug 2004 at 4:00, Jim N2EY, who eschews obfuscation, wrote:

> > Wanting to watch CATV on the screened in back porch (where running a
> > cable extension line would have been very difficult)...I  connected the
> > cable box output to a 3  stage class A amplifier chain (e.g. 2N5179 /
> > 2N5179 / 2N5109 I built w/ muliiple feedback at about 25 dB gain per
> > stage) and the output to a channel 3 (i.e. 62MHz) dipole. Then w/ a TV
> > set on the porch tuned to channel 3...I was able to receive wireless
> > CATV.

> By 'broadcasting' channel 3...

> > Not knowing the output level from the cable box.....I was lucky and
> > obtained about a 100' wireless  range.

> > Looking for any additional ideas on how I might refine this idea
> > further. For example, on further thought....I assume that the cable box
> > output is FM 

> It's not FM. It's a plain NTSC TV signal. Your TV could not decode an FM
> video signal.

Broadcast video picture is AM. Sound is wide FM on a subcarrier. 

That's why when there's a storm in the area and you're watching off air, 
the picture has noise but the sound stays clean.

If you do an amp, which is not a good idea, you will have a lot of work 
ahead of you. You'll need a broadband linear amp as you mentioned (sound 
subcarrier is 4.5 mgacycles up from the video carrier), and the amp will 
compress the video's sync so you'll have to build a sync stretcher. This 
will bump the sync level up so by the time it gets compressed in the amp 
you'll still recover enough at the other end to be usable.

To extend the range, improve your antenna, esp on the receive end. Try a 
simple dipole. 

There are cheap Wavecom or equivalent 2.4 gig license-free wireless 
video/audio boxes which will give 150 feet through inside walls if you 
play with the antenna positioning and don't need to penetrate any metal. 
They won't give more range than that unless you improve the receive 
antenna which is legal.
 
The work in small area coverage wireless video is done with antennas, not 
with power. See some of the White Papers on my website for details.

Steve WA3SWS


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Steve Uhrig, SWS Security, Maryland (USA)
Mfrs of electronic surveillance equip
mailto:Steve at swssec.com  website http://www.swssec.com
tel +1+410-879-4035, fax +1+410-836-1190
"In God we trust, all others we monitor"
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