A Baofeng field telephone for multiple users

[Fusionstate]

Tech question: Have you ever heard of connecting say, four Baofeng radios, in different locations in the field; 100 meter coax runs each, to a central junction box, for the purpose of setting up an Old School secure field set. If nothing else, perhaps simply running the coax, properly loaded, to a shielded, buried in the ground, junction box and extending the inner conductors as radiators should work? Four or more observation posts.

silverfox.

 

[brandon7861]

Why use RF equipment if running transmission line? Just send audio frequencies down regular telephone/speaker wire. There is the Plain Old Telephone Service, you can still use regular old telephones and a battery. At 100 meters, you could just use hand signals or IR transmitters and skip the wire altogether. Even cave man magnetic radio is an option. Coax seems like an expensive way to create such a small closed-circuit audio network.

If you did connect multiple baofengs to a central junction via coax, the radios would overload each other. Directly paralleling them would be an expensive lesson, and just extending a little of the inner conductor into the junction would cause high SWR on the coax and still may be enough RF to damage the other radios. You would need to terminate each incoming radio line with a separate resistor of suitable power rating matching the coax impedance and each of those resistors should have some sort of shielding from the other incoming lines/resistors to control the amount of coupling between them. And even then, enough RF will probably leak out of the coax system to defeat the whole purpose anyhow. You are literally burning tens of watts of precious battery power in the field to accomplish the task of what should be a µW signal.

If you want to use the radios, you would be better off turning the power setting to low and investing in attenuators to lower the power that gets to your antenna, using only what power is necessary to make the contact limits who else hears it..

 

[Fusionstate]

Thanks, It was a question and I appreciate the answer as I didn't have enough info to answer it myself. Again, thanks for the informative answer.

silverfox.

 

[Wire Weasel]

Tech question: Have you ever heard of connecting say, four Baofeng radios, in different locations in the field; 100 meter coax runs each, to a central junction box, for the purpose of setting up an Old School secure field set. If nothing else, perhaps simply running the coax, properly loaded, to a shielded, buried in the ground, junction box and extending the inner conductors as radiators should work? Four or more observation posts.

silverfox.

Many of the current Chinese HT's out there have Scrambler Mode. 10 Different selectable Voice Inversions. There's your Privacy.
A recently discussed model here on the forum is the Quansheng / Anysecu UV-5K

 

[Fusionstate]

Many of the current Chinese HT's out there have Scrambler Mode. 10 Different selectable Voice Inversions. There's your Privacy.
A recently discussed model here on the forum is the Quansheng / Anysecu UV-5K

I'm on my way to Amazon now, I'll have to check that brand out. Thanks.

 

[Shadetree Mechanic]

When I was a kid, my older cousin gave me some of his old walkie talkies. The ones that used a CB channel. I was fascinated by all the stuff inside, and all the adjustable cans that had a screw driver slot in them, obviously they were made for a screwdriver. So one day I decided to find out what they do. While talking to myself, I would make an adjustment and key and talk, adjust key and talk. I came to the conclusion that those adjustments did absolutely nothing. Then I got my sister to talk on the other one, I could not hear her, and she could not hear me! OH NO! How to adjust it back? I could not figure it out. So the next solution was to connect the antennas with a long piece of wire. With my sister in the next room, it kind of worked. For a few minuets. And then that was the end of that. So I learned early on what not to do............

 

[Fusionstate]

When I was a kid, my older cousin gave me some of his old walkie talkies. The ones that used a CB channel. I was fascinated by all the stuff inside, and all the adjustable cans that had a screw driver slot in them, obviously they were made for a screwdriver. So one day I decided to find out what they do. While talking to myself, I would make an adjustment and key and talk, adjust key and talk. I came to the conclusion that those adjustments did absolutely nothing. Then I got my sister to talk on the other one, I could not hear her, and she could not hear me! OH NO! How to adjust it back? I could not figure it out. So the next solution was to connect the antennas with a long piece of wire. With my sister in the next room, it kind of worked. For a few minuets. And then that was the end of that. So I learned early on what not to do............

As mentioned in the initial post: "perhaps simply running the coax, properly loaded,"

Perhaps I didn't specify it sufficiently, and at this point, I'm sold on the principle that it's not practical to, "field telephone" handhelds. But if I did try it, I would incorporate an Impedance network to properly couple the transmission lines to the handhelds. Another possibility would be to use a distribution amplifier; If there is such a thing?

Perhaps there is no way to properly feed a piece of coax in some, "Broad Band" manner.

I do appreciate the feed back though, and amused by your story. The things we did as kids- I can't image any of those experience's being had today by the children of the present age. Perhaps a few of them.

Regards.

 

[Woody-202]

Many years ago my friend Dana lived behind our house and it was a straight shot from my room window to his. We hooked 2 coffee cans with a string between them for covert conversations. Unfortunately we soon found out that our secure line wasn't so secure because we were shouting into the cans, so 1/2 the neighborhood knew about it.

 

[brandon7861]

Amazon sells really cheap laser modules (with the beam receiver included) for a couple bucks. You can audio modulate the laser and receive it by connecting the photo sensor to an audio amp. It is reasonably linear if you get the laser drive levels right. Here I had my scope connected to the photosensor and the laser connected to my sig gen with a 500Hz sine wave at .9v pk-pk with a 4.3v DC offset.

Edit: you will need a decoupling cap between the photo sensor and amp to block the DC from the laser bias (its always on, just to a different degree) and have the laser and receiver fairly stable because the change in DC offset from changes in the laser alignment will also be amplified. Since the laser will have a DC bias too, the audio input will also need a DC blocking cap.

 

[Captain Kilowatt]

Why use wires to communicate via a wireless system? It WILL radiate so it will NOT be private. If you want privacy and a closed system use old telephones with the carbon mikes, a battery of some voltage 12-48volts and you have private comms.

 

[Hurricane145]

When I was a kid, my older cousin gave me some of his old walkie talkies. The ones that used a CB channel. I was fascinated by all the stuff inside, and all the adjustable cans that had a screw driver slot in them, obviously they were made for a screwdriver. So one day I decided to find out what they do. While talking to myself, I would make an adjustment and key and talk, adjust key and talk. I came to the conclusion that those adjustments did absolutely nothing. Then I got my sister to talk on the other one, I could not hear her, and she could not hear me! OH NO! How to adjust it back? I could not figure it out. So the next solution was to connect the antennas with a long piece of wire. With my sister in the next room, it kind of worked. For a few minuets. And then that was the end of that. So I learned early on what not to do............

Great story! Reminds me of ME back in my early radio days!

 

[Hurricane145]

A few tin cans and a lot of string may work!!