Blonder Tongue Modulator Modification

[vts1134]

I've been working with my Blonder Tongue modulator recently to try and fix an issue when I broadcast with a dipole antenna, unfortunately I couldn't resolve it and went with a hardwired connection to all of my sets in the end. It did get me thinking however and I wanted to ask the much smarter people in the room for their opinion. I would like to modify one of my modulators in two ways. First, I want to set the channel frequency to channel 1. All of my sets have channel 1 and I think it would be neat to utilize this channel. Second, I want to modify the audio portion to broadcast in AM instead of FM. Some of my sets have AM sound and I would like to feed them with an AM signal. I know I can use slope detection for my audio, but I want to get an AM signal instead to get strong, stable audio out of my sets. Does any one have any thoughts on the idea? Is it feasible?

[Electronic M]

IIRC those units also can transmit on analog cable channels. There may be an analog cable channel that operates on the SAME frequencies as the old broadcast channel 1, and a channel one by any other name will still receive the same provided the frequencies jibe.

[ChrisW6ATV]

Anything is possible if you try hard enough. I know there is at least one modulator that can be directly set to channel 1, the Olson Technologies OTM-3000. Changing FM audio to AM is also possible, but not trivial.

To do any of these type of projects, it would help a lot to have some knowledge of RF and modulation circuits. One book that is very good is the ARRL Handbook. It is published by and for ham radio operators but is an excellent source of RF information for anyone. There is a new edition every year, but the basics have not changed in years, so you could find a bargain looking for any edition from the last 15-20 years or so.

[WISCOJIM]

Originally Posted by ChrisW6ATV

Anything is possible if you try hard enough. I know there is at least one modulator that can be directly set to channel 1, the Olson Technologies OTM-3000.

The manual says it only goes down to 55.25MHz, Ch. 2.

http://www.olson-technology.com/Manu...000-Manual.pdf

.

[ChrisW6ATV]

You are right about that manual. Then, I either figured out the code with the DIP switches and found it would go down to 45.25, or maybe I am wrong about the model number and another one goes to Channel 1. Maybe it is an OTM-1000. I should look to see what I have here.

[ChrisW6ATV]

Wiscojim-

I got curious and just tentatively re-figured out how to get Channel 1 from the OTM-3000. Looking at the code in the DIP switch settings, if you skip the left-most switch and concentrate on the next seven, you will see they are in reverse order (lowest bit on the left). So, the decimal numbers and resulting frequencies in whole MHz go like this:

DIP...... dec freq (add 0.25 MHz)
1001110 78 55 MHz
1010001 81 61
1010100 84 67
1011001 89 77
1011100 92 83
1100000 96 91

You will see a logic. Every digit higher equates to 2 MHz, with 78 equaling 55 MHz. So, subtract 5 and you should get 45 MHz:

DIP....... dec freq (add 0.25 MHz)
1001001 73 45?

This equates to switch settings in the format of the Olson manual like this:

SW1....... SW2
01001001 01000

I am pretty sure I tested this with my unit, but I did not have a restored TV set that could tune to channel 1 at the time, so I did it in some indirect way (such as looking at a spectrum analyzer, or tuning a VHF audio scanner and hearing the carriers or similar). Now that I have an RCA 8TS30 restored, I should hook up the unit and find out for sure, huh?