2
$\begingroup$

I have a TV antenna on the top of my house that I don't use. It is the highest point around so I would like to hang a wire antenna (for HF) on it. Is an inactive antenna going to cause any interference? I found this, but I think it is different because I don't care about affecting TV reception.

As for antenna configuration, I will probably first try an end fed half wave with the wire going over the TV antenna about 75% of the way from the feed point. I could also attach it at the far end of the wire. If it helps I am hoping to use 20m 40m or 80m.

$\endgroup$
1
  • 1
    $\begingroup$ Thank you webmarc! I will edit my question now. $\endgroup$
    – Bill H.
    Apr 26 at 21:49
3
$\begingroup$

Of course, the answer to this question is certainly "it depends."

Yes, different antenna elements in close proximity can interact and cause interference problems. The most notable issue would be a degradation of both antennas. You don't want that.

But you might not have a problem - again depending on what sort of antenna you wanted to put up, and what sort of orientation the respective antenna elements would have with one another.

Now, I'm going to assume that you are not using the TV antenna at all, so let's not worry about any deleterious affects there. The primary question would be, would the TV antenna affect an antenna hung from the same support.

For example, if you used the TV mast to anchor one end of a 40m dipole, I doubt you would have any problems, particularly if the dipole element tips were 5-10 feet away from the TV antenna.

If you used the TV mast to anchor the center of a 40m Inverted-V, you might have a little bit of interaction with the TV antenna -- moreso than you would have with the ends of the 40m dipole.

That said, we Amateurs typically mount several antennas on a support, generally with some vertical separation. At my station in Gwinnett county, I have a 15m (50 foot) tower with a Cushcraft A3S / A743, an 80/40/20m trap dipole with one end anchored at the 12m (40 foot) level of the tower, and a 30/17/12m inverted V, whose apex is at 13m (43 foot) level of the tower. All of these antennas are in close proximity, but are mostly for different bands (the dipole and Cushcraft have 40 and 20m in common). From my testing, I don't see any interaction between them.

If you aren't using the TV antenna, I would suggest you take it down and use the mast as a support for whatever antenna you like.

Enjoy.

$\endgroup$
5
  • 1
    $\begingroup$ Hi Bill, and welcome to ham.stackexchange.com! $\endgroup$
    – rclocher3
    Apr 27 at 16:50
  • $\begingroup$ Hello Bill, and welcome! You said "If you used the TV mast to anchor the center of a 40m Inverted-V, you might have a little bit of interaction with the TV antenna -- moreso than you would have with the ends of the 40m dipole." Why would this be so? The high Z points are at the ends. :-) $\endgroup$
    – Mike Waters
    Apr 27 at 21:50
  • 1
    $\begingroup$ @MikeWaters - the reason is simple. At the ends of a dipole antenna, there is virtually no current flowing. At the center of a dipole, most of the current is flowing. Those flowing currents set up large fields that can interact with the TV antenna, perhaps destructively. However, having several dipole antennas cut for different frequencies doesn't always have to be destructive. This is the way an OWA cell works, and is the basis of many antennas from Force 12, JK Antennas and others -- where elements are carefully placed to interact in a positive fashion. $\endgroup$ Apr 28 at 19:33
  • $\begingroup$ Thanks, Bill. Hey, do you know Tom Rauch? I see you quote him on your blog and realized that you live near him. I've known him for over 40 years! EDIT: Comments such as this should be taken to Ham Shack. Now that you have over 50 rep, you can chat there. It doesn't get used near enough. $\endgroup$
    – Mike Waters
    Apr 28 at 23:02
  • 1
    $\begingroup$ @MikeWaters - yes, I know Tom, although it has been years since I've last seen him. He has certainly set me straight on a number of topics over the years. He knows his stuff. $\endgroup$ Apr 29 at 15:05
1
$\begingroup$

Just using it as a support will definitely have some kind of interaction with your antenna, unpredictable but empirically measurable.

BTW, my first thought is that you can try to take advantage of that TV antenna as a capacitive load at the end of your EFHW (make sure to disconnect the TV antenna from any feed line of its own though).

Using it like this will shorten the wire you need for the EFHW, and you'll need to use an analyzer to be able to sanely tune for the bands you want.

Regardless, definitely worth putting it up and giving it a shot!

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.