Blonder Tongue Modulator, Multiple Units
 

I use an older AM60-550 for broadcasting a nice strong TV signal to my propriety. It makes using my old analog portables a complete and total delight.

I'm waiting to set up at least two more of these, giving different channel options to my TV's. Such as Consoles Games on one channel, movies on another, and rebroadcasted digital TV to another channel for news. That way I can just pop though channels on the analog sets and never have to disturb my transmitter to change what it's broadcasting.

These things are supposed to about 13mW, give or take to the antenna.

What I want to know is can I feed these units though a splitter in to a single antenna, or do I have to have an antenna for each unit?

It is possible, but there are issues that may need to be addressed. First the splitter/combiner will introduce losses that may or may not matter in achieving your desired signal range. Another possible issue is whether or not the output from one unit could damage another...Also there is the chance the two will beat against each other and cause interference or harmonics/carrier drift.

I have three modulators each with a different antenna that I made out of lamp cord cut to the frequency of the desired channel (Shango66 has a great how to video about this on youtube), each one from inside on the second floor can be received at least to the edges of the lawn, and the best one one can be received about a block in each direction.

I try and limit the range to less than that and use channels that I can't find any DTV carriers on so I don't tick anyone off....Though I've been wanting to design an RF booster based on spare sweep tubes and try to see how many miles I can cover as a pirate station on the holidays and whenever.

That is what I was thinking too, is that each modulator will stumble over the other, or damage each other trying to force though a splitter to a single antenna.

I have an old 4-Tube Sweep amp, runs on 4 6LQ6 tubes. I bet I could re-tune it to work on the real low VHF bands and give up some power if I felt creative.

I looked over frequency charts before I picked open channels I could potentially use on VHF. Channel 8 was always open in the Analog days here, and Channel 13. I don't think there is much from 2 to 13 in this area, but to be safe I use 13. Seems to give the best results. In the analog days, it was WREX from Rockford, which, even on a big bream antenna aimed at Rockford, it never came in well here, so even if it's DTV signal is sitting there, I am not bothering anyone.

Blonder Tongue does make rack mounted passive combiners for combining the outputs of multiple modulators at cable head ends. I think some models can combine up to 24 modulators. Here is one example on the 'Bay:
http://www.ebay.com/itm/Blonder-Tong...item1c38a0373f
While these passive units *do* combine outputs of multiple modulators and provide proper isolation between modulators, the penalty is considerable attenuation (-16db) of the output signal to the cable system, or antenna in your case.

jr

That sounds like a neat starter rig. I really need to go to some hamfests and look for some homemade 6 meter RF TX amps (which is close-ish to low VHF channels) to try and convert to TV VHF.

If you happen upon a cheap Zenith/LG/insignia DTV box I'd recommend grabbing it. They have really good RF systems capable of getting in weak signals well. I picked the modulator channels on my modulators by using the manual add channels mode on my DTV box to look for empty channels...In that mode the box shows the actual RF channel along with a signal strength meter so a channel that would be missed in a scan, that I might be able to pickup with a better antenna is properly noted.

Lowband VHF is virtually a ghost town so it is often a good place to tune agile mods, and the sold off portion UHF spectrum is probably decent too.
The UHF band tends to be really packed below CH 50 here these days.

Why not use an active combiner? They're very cheap.

http://www.ebay.com/itm/291360722532

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Perfect! that is *exactly* what is needed!

jr

Nice. I have been wondering how to go about doing this. I'll probably hard-wire the whole thing though.