Because I do a lot of military monitoring, I find a need to combine multiple radios in different ways. In the car, I feed multiple handhelds from a single antenna. But to escape from the car to a lawn chair--particularly in a high-noise environment--I need to feed all the radios into noise-reducing phones or buds. This setup keeps the radios organized and accessible, feeding a headphone amp thru a mixer, and allowing me to power them from USB power packs. Materials came from Walmart, Lowes, CVS and Amazon. It all fits nicely in a thrift store valise along with cheat sheets (in plastic display pockets), notepad and extra cables, etc.
Combining Multiple Handhelds for single audio output
- Thread starter n4jri
- Start date
dispatchgeek
Control channel goes "brrrrr"
Fine work! I might steal this idea from you 
Great idea! What is the device on the lower right in pic 5290? It seems to have no leads to it.
The OP can correct me if wrong, but I believe a headphone amplifier.
OK, so the mixer feeds the amp, then the speaker or headphones connect to the amp I assume.
Correct. At the time I took the photos I hadn't found a short lead to connnect the mixer output to the speaker amp. If you look on the side with the radios, you'll see that I was also missing a USB power connection to one of them.
While I do like that the TRX's headphone jack is wired for stereo earphones/buds (despite a mono output), the world of mixers has been slow to catch up to this. Both mixer and amplifier were in the $30 range. In fact the same folks who make the mixer make a 4-output headphone distribution amp.
I bought my amazingly scanner-tolerant girlfriend a set of Koss noise reducing headphones to protect her ears from all the jet noise coming from the airshow, but also hooked her up to the unit with a Y-adapter so she could hear the Thunderbirds. It was a very positive step toward further scanner tolerance. Am also planning to experiment with an amplified speaker.
One regret I have is that I was in a hurry to build this for the airshow at Langley AFB. Because I'm using that 3M hook stuff (like they use to mount smart tags on a windshield), to mount the mixer, amp, and join the two boards, I'm a little wary of the fiber clipboards. I may replace them later with plastic clipboards--now that I can use them for drilling templates.
If anyone wants to build one yourself, just let me know if you have any questions about the materials used. The hardest stuff to get was the angle pieces, but they can be found in the 'hard to find' drawer at Lowes. All are Hillman products. Used #6 nuts and bolts for most mounting. 3/8" for most stuff and 1/2" for the D-rings that I mounted double.
73/Allen (N4JRI)
Next you can get a BT transmitter and use wireless headphones.
You might consider something like this that will take in receive audio from 6 receivers or receive and mic audio from transceivers. Then its got a single really loud amplified speaker with individual level controls for each radio and one mic will work on any of the 6 transceivers. It runs off 12 to 24v and is not very big for what it does.
LOL…fixing up the connectors would like cost way more than my entire project!
eBay usually has connectors or I was thinking of putting an RCA jack below each M/S connector for connecting cheap stuff. Or another trick is get cheap female pins, slide them over the male audio input pins then cover the audio cable to the scanner and chassis connector where it exits with heat shrink for a strain relief.
In fact, that headphone amp has a bluetooth receiver. Might be fun in the other mode...where the scanners are left in the valise discretely recording
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