Help Understanding RF Transmitting

[TinCanAlley]

So here's what I want to do, but I need some help understanding what is needed so I can get the setup right the first time.

I currently have several RF devices (laserdisc, VCR, etc.) that I want to transmit and ditch the coax. My first step was to get the Archer Video Distribution System that will take three RF inputs and output all three on a single RF out and you access each by tuning to a certain UHF channel. What I want to do now is take one of those RF outputs and send it through an RF amplifier to transmit it so each TV in my place can tune into one of those three channels.

So here is what I need help with.

What kind of power would be necessary to transmit a signal strong enough to cover 2000 sq ft. Not looking to send it far as each TV would be within 20 feet of transmitter and maybe one wall.

With the power amplifier, is it as simple as connecting a pair of rabbit ears to it for transmitting, or do I need something tailored to the channels I want to broadcast?

I've read several posts here recommending the BT AM-60, but it seems a little overkill for what I need. Is it? If not, does it take a simple RF signal as input or do I need to do more signal conversions?

Anyway, thanks ahead for all the great input I'll get (as usual).

[Electronic M]

Amplifying your archer video distribution system is not a practical thing. There aren't really amps out there designed for that sort of thing especially at UHF.

You need 40-60 dBmV to get good results especially if your antenna isn't optimized for the channel.

The Blonder Tongue Modulators take line level audio and composite video (the white and yellow RCA jacks on the back of your VCR)... Blonder Tongue uses F-type connectors for RF output, line level audio and composite video...they use RF style connectors for non-RF signals because they were designed for cable television head ends where only screw connectors are acceptable (RCA connectors can be yanked out which would cause many nightmares for their technicians). They make little F-type male to RCA female adapters that are like 1$ each that convert the Audio and video jacks on a Blonder Tongue to the RCA connectors we need.
Just about every VCR and Laserdisc player ever made has RCA composite video and line level output as do most video sources...2 exceptions I can think of are early RCA CED video disc players and some Atari era video game consoles that only have RF output...my basement transmitter has such a CED player and several such game consoles...I tune them on the VCR and feed the composite output of the VCR into the Blonder Tongue to transmit those

There are 4 different Blonder Tongue models I'm familiar with that will do the job of transmitting. There are AM-60 model 60dBmV that can cover a block with the output level set to max, the AM40 40dBmV which can cover 2 houses at full output, the BAVMz family that is halfway between the output of the other 2, and there's some mini modulators, which I have never used, that a bunch will fit in a 2RU power supply/mounting system. The AM series are agile modulators meaning you can change which channel they output. The BAVM series definitely and possibly the mini modulators too are fixed channel so if you buy a unit for channel 2 it'll only ever transmit on channel 2. The agile modulators have the final 3 digits of the model number as the max frequency they can transmit (an AM60-400 can only do VHF, a -550 can do VHF and low UHF, a -860 can do VHF and all UHF). Something to keep in mind with the fixed channel modulators is channels above 14 are cable channel numbers which operate on entirely different frequencies than UHF channels with the same channel number... Some cable channel frequencies overlap with some UHF channel frequencies, but you have to use frequency to translate (IIRC cable 66 is around 16 UHF)... some cable channels are in the FM radio band, some are below VHF some are between TV bands some are above UHF and it jumps around and there's 2 different cable TV frequency schemes IRC and HRC so it can be a PITA to do UHF...

Some Blonder Tongues need recapping at their current age and setting up a good antenna is a process I've written about so many times on videokarma that I rather you search my old posts.

[TinCanAlley]

If I got a wide band amp, wouldn't that be able to amplify all three of the channel frequencies output by the Archer? If so, is that where the antenna issue comes in? I'm guessing it's not as simple as rabbit ears on the transmitter and rabbit ears on the TV.

[Electronic M]

Originally Posted by TinCanAlley

If I got a wide band amp, wouldn't that be able to amplify all three of the channel frequencies output by the Archer? If so, is that where the antenna issue comes in? I'm guessing it's not as simple as rabbit ears on the transmitter and rabbit ears on the TV.

I doubt you'll be able to find a amp with enough bandwidth and power. All amplifiers have a rating called the gain bandwidth product (it may not be a published spec depending on application). Basically it means there's a trade-off between passband bandwidth and gain....
Most antenna amps that are wideband enough to cover multiple TV channels are going to not have enough power to transmit (they also didn't want their amps transmitting). Also the higher the frequency the harder it is to make a good amp for it.
The only thing that might work I can think of is Blonder Tongue made an amplified combiner for their agile modulators when might work.

In antennas there's a similar trade-off between bandwidth gain and size... It'd be most noticeable on the transmit end. 4 separate antennas each optimized for a channel and connected to only the modulator for that channel are going to be better than one combined transmit antenna fed by multiple modulators.

You can try what you want to, but I don't know of anyone who has gone down the path you proposed with that archer box so if you are set on using it to transmit you're probably going to be basically on your own troubleshooting your own unique problems that may or may not have solutions...that if they exist may not be easy solutions...If you like that sort of solo challenge it could be fun.

What I outlined in my previous post is the way that is known to work and will have the most support since many collectors are using Blonder Tongues and most of their issues and the solutions to them are known...if you want an easy transmitter go with a Blonder Tongue, another cable grade RF modulator (there are other brands) or a hilly transmitter.