What would happen?
Would it over load people's radios and have a mix of both if they had the same out put?

When I was in my childhood I was having two smart kit vco I did that and nothing happen .with different type of antenna .it was funny

Maybe I should give it a go be funny to see the results and even when going far away to see what one tries to come in.

Not unless you tried to put two rigs into the same aerial!

Albert H wrote: ↑Sun May 07, 2023 8:23 pm Not unless you tried to put two rigs into the same aerial!

I've done exactly that, using a custom designed duplexer and multiple cavities, two frequencies at each end of the band 87.6mhz and 107.5mhz, fed into a dual band dipole. It's mounted up on a steel truss tower with comms repeaters on the same tower. One of the comms repeaters in on around 165MHz transmit, and the receive is 168Mhz thereabouts. The whole setup has been running without any issues for the past 4 to 5 months, although just yesterday the comms guy's complained they could hear the program from 87.6 on their receive on 168Mhz - it's gradually washing in and out over a few hours in the afternoon - easily heard on their portables when holding the channel open.

Now I have to get up there with my analyser and find out what's causing it. The plan is to try a coaxial trap first. The whole setup was tested for intermods when installed, and they were very low down below the noise floor. Theres other stuff on the same tower too, another repeater on 85Mhz receive, transmit on around 82Mhz - for that one the comms guys had to use multiple cavities on their receive, one with a deep notch on 87.6 otherwise they lost a lot of receive sensitivity on 85Mhz

I assumed that the original poster just meant connecting two rigs together.

I have recently been involved in diplexing four transmitters into the same antenna: These rigs were in the 40kW class, and the diplexers were specially constructed for the specific group of frequencies. In the event, there was virtually no adjustment needed on site (which was very surprising!). Everything up that tower went through cavity filters, and there were some (small) intermodulation issues which were tweaked out in the relevant receiver input filters. We were lucky, I suppose, because there were no receiver (or repeater inputs) operating anywhere near any intermod mix or harmonic frequencies.

Incidentally, some years ago in Eastern Europe, we ran two transmitters on the same frequency - both phase-locked to a common link to keep them phase-coherent - separated by about 4 km. One was about 800W and the other was around 200W. Trying to locate the source of the transmission with the normal Doppler DF gear proved to be virtually impossible!

turn off one by one and easily without instruments you will find the cause

Years ago I would mess about with fm local oscilators in radios when you couldn’t get any other transmitters, sometimes when i’d put them both on the same frequency I could get the stereo light to come on.
Two transmitters on the same frequency won’t do anything, if you put two which were doing a few watts from the same place on different frequencies, I imagine you’d get more intermods on your radios, like you’d do if you went to a place where they broadcast radios 1-4, mixture of the strongest stations with whatever you’ve got going. I’ve spent so much time in the past trying to find pocket radios which don’t have them, as theres nothing worst trying to pick up your signal hearing just mixture of other radio stations.
It may depend on the quality of the radios and transmitters, the power of them, i’m thinking if they were cheap chip transmitters one might have a perfect match, the other might not so you might get spurious, having 2 going would make it more likely, if there were just 0.1w transmitters it wouldn’t matter. You could get higher quailty transmitters, PCS ones are quite good they withstand a mismatch, have thermal protection, unless you’ve got 1 that is a dud, they won’t put out spurious, they probalby could be left going.
As long as your not trying to connect the rf from one transmitter trying to amplify it, then it won’t harm either, you could always check on one of those tiny handheld spectrum analyzers by turing one on then turning the other offending article off, making sure just the harmonic frequencies are present, so your transmitter frequency times 2, example 87.8 x 2 = 175.6, then you go 87.8 x 3 = 263.4.