Combining Rf signals to amp

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
I am working on a wifi A/V project that uses 4 TX6729 2.4GHz FM A/V transmitters (4 A/V sources, etc). Each runs on a different 2.4 channel. I would like to mux them up to one Rf amp. How can I combine their outputs?
 

KeithWalker

Joined Jul 10, 2017
1,918
Can you be a little more specific in your question?
What are your sources; audio, video or both?
What format is the data in? Are all four channels in the same format?
What do you plan on doing with the resultant multiplexed signal? Are you going to de-mux it back into 4 discrete signals or are you going to just use the combined signals?
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
The small 6729 A/V modules have inputs for audio and video, it then mux's that up into 2.4GHz carrier using FM. Each runs on a different set of 2.4GHz channels.
I have 4 security A/V cameras and want to transmit them via one amp and one antenna. It's unidirectional only, from remote location to a monitoring station. The de-mux is fairly easy because each A/V camera rides in it's own 2.4GHz channels.

There are many COTS A/V "wifi" cameras to be had, so think of it like buying 4 COTS items, setting each to be on different 2.4GHz channel, and then wanting to feed all 4 into Rf amp and then out via one antenna.

I can do it with an amp and antenna for each A/V camera, but getting it down to one amp and one antenna would simplify the amount of hardware & costs.
 
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Thread Starter

DC_Kid

Joined Feb 25, 2008
806
I am thinking a simple passive 50ohm diplexer (a 4ch one) will suffice, like this Wilson item. The passives work bi-directional. Although I may need to add an attenuator so as to not swamp the input on amp.
Thoughts?
 

Yaakov

Joined Jan 27, 2019
3,501
I am thinking a simple passive 50ohm diplexer (a 4ch one) will suffice, like this Wilson item. The passives work bi-directional. Although I may need to add an attenuator so as to not swamp the input on amp.
Thoughts?
Are you talking about an amplifier feeding the antenna?
 

KeithWalker

Joined Jul 10, 2017
1,918
I can do it with an amp and antenna for each A/V camera, but getting it down to one amp and one antenna would simplify the amount of hardware & costs.
NO! It would increase the hardware cost immensely. You would need a transmitter and receiver with a much higher frequency then Bluetooth if you want to modulate it with even a single 2.4GHz signal. Using four signals of different frequencies mixed together as a modulating signal would require a very complex custom demodulator to recover and separate the original four 2.4GHz signals. What ever is receiving that signal would require two way communication for the 2.4GHz signal handshaking protocol. Are you capable of designing and building such a system?
The obvious way to do it would be to have an inexpensive tablet connected to each camera via Bluetooth and networked to the internet. If you don't have remote internet access, it would probably be much cheaper to subscribe to a basic satellite data service than to buy a lot of very expensive high frequency transmitting and receiving equipment.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
Each 2.4GHz channel is ~22MHz wide.
I can't feed a channel 1 (2412 ±11) and a channel 10 (2457 ±11) into a passive diplexer to combine the two? A diplexer used as a combiner, perhaps in Wilkinson config for isolation?

It's 2.4GHz FM modulated, what handshake? It's not 802.11.
 
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Yaakov

Joined Jan 27, 2019
3,501
To amplify the signal.
This is almost certainly not legal. The ISM band power is limited to 30dB (1W) input to the antenna, and if you have a gain antenna The ERP is limited to 36dB (4W). If your intention for the amp is to make up losses in the transmission line and diplexer that’s fine, but you can’t exceed the ERP, legally, so you’ll have to calculate that and reduce the input to the antenna to meet it.

You will need this entire setup on each end, of course, and any amplifier you use must be able to deal with a transceiver, that is, it must be able to switch between transmit and receive as needed.

I think you’d be better off with a simple array of four yagis on each end, but you still need to respect the 36dB ERP limit,\.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
I am well aware of max power limits. Max range and best signal (using crap components) will come from max allowed power.

Why would the sending side need to be a transceiver? It's only sending data, never gonna receive data. It's send on one side, receive on the other.
 

Yaakov

Joined Jan 27, 2019
3,501
I am well aware of max power limits. Max range and best signal (using crap components) will come from max allowed power.

Why would the sending side need to be a transceiver? It's only sending data, never gonna receive data. It's send on one side, receive on the other.
Sorry, I realized I was thinking of WiFi, same band. Just a mental habit, broadcast is different. I am glad you are aware of the legal limitations, so many are not. 2.4GHz is a shared band and interface is a serious problem in some places.

You may find you have trouble with adjacent channel interference though. Do check the channel spacing and bandwidth specifications. If the center frequencies are too close together they may overlap and interfere with each other.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
wifi channels are just 5MHz apart, but are 22MHz wide. It's a bit of overlap for adjacent channels. I certainly do want to choose channels that minimal overlapping, like 1/5/9/13.
 

Yaakov

Joined Jan 27, 2019
3,501
wifi channels are just 5MHz apart, but are 22MHz wide. It's a bit of overlap for adjacent channels. I certainly do want to choose channels that minimal overlapping, like 1/5/9/13.
This *isn't* WiFi based, right? Also, when you mix these channels in a diplexer the interaction may be much worse than in physically separated free space.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
806
Most think of "wifi" as implementing 802.11, but no 802.11 in this project.
I kinda use "wifi" loosely in regards to the 2.4GHz band using the channel centers designated by "wifi".
It's bad use of the nomenclature/lingo for sure. The FM A/V modules broadcast out on a "wifi" channel frequency.
This is a DIY project for me, so I will test w/ and w/o using a plexer (and no amp) just to see what issues I may run into.
 
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