Ham radio question

To you seasoned veteren HAMs - I'm currently putting up a 2m/440 vertical antenna (Diamond X-50) on my home - was wondering how far you need to keep it from a TV antenna (with a pre amp) to prevent damage ? Right now I have it mounted just above (8" aprx) the TV antenna on the same tower but am concerned that it may damage the pre amp or TV - so I haven't tried it yet. Thanks for any info.

Jon Miller
If you are going to put out anything over a couple of watts, I would definitely give yourself more space than that. I don't know that there is a specific distance, but I don't know that 8" would be sufficient. I've never had mine closer than 10ft, and I've never had any problems. You could try it on LOW power and see if you notice it. Step up the power a little at a time.

There has to be a better answer than what I just gave, but that's been my experience thus far.

When I mount my antennae on masts or seperate poles, I always try to keep them just over the 1/4 wave apart.
I have antennae for 50Mhz,144/145 Mhz, 430/440Mhz and 1.3 Ghz UK ham frequencies, also 137Mhz Turnstile for WX Satellites,

Receive only antennae are on the same mast,FM radio,Digital Radio(DAB) and TV3 but all TX stuff at least 3m away from the receive stuff.

No Interference from TX up to 50W rf output.

UK ham since 1986 (G1GTV)
There are two major factors to consider in this scenario...

1) A TV antenna is horizontally polarized, and a 2M/440 vertical antenna is vertically polarized. Simply put, this means the antennas "see" on planes perpendicular to each other. This will greatly reduce (attenuate) the amount of RF energy passed to your TV antenna when you transmit.
EDIT: Also, your TV antenna being directlt under the vertical puts the TV antenna in a null of the radiation pattern of the vertical, which means the least amount of RF energy possible is radiated in that direction. I can E-mail you a screenshot from my antenna modeling software to demonstrate this if you like. :D

2) VHF TV operates just above the 6 meter ham band (50-54MHz), while 2M is higher in frequency (144-148), UHF is even higher (420-450MHz) These signals will be further attenuated in your TV antenna because it is not tuned to recieve those signals. The exeption will be if you watch UHF TV, which is very close to the 440 band.

I used at my old house, a diamond SG-2000 2M mobile mouned right on top of a TV antenna with little or no RF interference TO THE TV, however, stereo and computer speakers picked up a hum. I ran 50 watts at times with no damage. In fact, the TV antenna acted as a ground plane for the vertical, focusing more of my RF towards the horizon, yielding a better signal (higher gain).

I doubt you will do damage, but you may desensitize the reciever in your TV when you transmit. It would be wise to test at lower power levels first.

Let me know the results, I'd like to compare them to my own experiences. If you have any other ham related questions, don't hesitate to PM me.

Your friendly neighborhood Extra,