[drgordon]

There is a problem with combining ANY signals from aerials pointing at adjacent transmitter groups - from reflected ie out-of-phase signal images; your antennae are picking up in a lobar pattern - stronger in the "forward" direction, where the aerial is pointed - but picks up some signal from the 180 degree opposite ie back of the aerial.

If you can put some shielding BEHIND the aerial (a water tank in the loft, in my case) it will block a lot of this. Essentially, any grounded metal plate NOT ELECTRICALLY CONNECTED TO THE AERIAL SYSTEM, but erathed to ground, should reduce the back-of-beam signal.

I am a licensed radio ham, and I use this to keep the signals from my 2m ham, DAB receiver aerial, massive high-gain FreeView aerial, and PC signals (wifi, etc) separated. I have main transmitters at Brighton and Isle Of Wight TV (analog & Freeview), a relay station a mile or two away, and most of the French coast using more power on the same frequencies, and only analogue TV on BBC1 & 2 is adversely affected - French TV seems to run 1000s of times the RF power that the UK use, and spread it around like a dose of pox!

If you really MUST combine, try using a frequency mux-demux unit, which combines multiple signals - look in most satellite TV mags for ads and reviews, they use them to combine the outputs of multiple satellite dishes to feed to multiple or the same receivers, and I don't thinkthey were _that_ expensive. But try shielding the rear of the beam first, e.g.

A ! F A
/ \ ! I / \
/ \ ! I / \

Transmitter SHIELD Your aerial Other transmitter

Dave G6ENT, with multiple aerial for multiple transmitters, receivers, etc