BNC tee's and splitting feedline to multiple locations

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Bob Lewis:
BNC Ts are not splitters. Splitters use inductors and capacitors to divide the signal across several runs while maintaining the impedance match. Every time you 2-way "split" the signal you loose half plus the loss in the splitter. Half the signal goes down each coax run. Splitters can work in receive only systems because you can use a pre-amp at the input to make up for the splitting loss. It won't work properly with a transmit system like an HT. Either use a switch or make a BNC patch panel where you can connect only one coax run to the antenna.

Bob Lewis:
Think about it this way. Your HT transmits 5W. It goes thru the first splitter. 2.5W heads towards the antenna and 2.5W goes into the unused cable and eventually gets consumed by the termination resistor. Next the 2.5W heading towards the antenna hits another splitter where 1.25W heads towards the antenna and 1.25W heads into the other unused cable and eventually gets consumed by the termination resistor. Every time you do a split you loose half your transmit power. This all assumes no loss in the splitter itself, but they actually add another 1dB of loss, approximately.

This is a very bad design. Don't use splitters or Ts.

Steve Katz:
A coaxial switch on the main feedline is the answer.  If it's inconvenient to access that particular point, you can use a "remote" coaxial switch where the RF switching is at one location and the control box to select the active port is at another location.

Matthew H:
Yeah I just talked to the guy who pushed me to get my license etc (my local Elmer, I guess you would say) and he pretty much told me he was surprised my radio is still WORKING after a 10 minute contact using the setup I'm using.

I'm going with separate runs, and manually switching them out until I can build a multi-radio/multi-antenna switch.

I think I learned a lesson, without blowing up my radio...which is a bonus. Most lessons end way worse than that.

Thanks guys. I'll think a bit more before doing stupid crap like this. Admittedly...I created this set-up when I was receive only, and I should have known it would be wholly unacceptable for transmitting.

Slightly embarrassed, but I won't make the mistake again!

Dale Hunt:
Actually it COULD be made to work if the coax lengths are cut just right, but that
likely isn't the case.

Power does NOT split evenly at a T connector.  Rather, both lengths of coax see the
same voltage across them where they are connected in parallel, and the actual power
flowing in each leg depends on the impedance.  If the open section of coax is a multiple
of an electrical half wavelength that leg will look like an open circuit and most of the
power will flow into the other leg.  But if the open coax is a quarter wave longer that
leg will look like a short circuit (except for some residual resistance due to cable losses)
and the rig will see a high SWR.

Using a switch has a much higher chance of success.  With an appropriate application
of switching relays you could arrange it so a switch at the end of each coax would
cause that one to be connected to the common antenna:  that would free you from
having to walk back to the shack to flip the switch when moving from the porch to
the living room.


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