How far apart is far enough apart?

[sallen07]

Quick background. I've been into scanning for quite a few years but just got my amateur radio license this spring. I have a motley array of antennas inside for my scanners, and while I can actually pick up more than I can listen to sometimes, I know there are other things I could hear (or hear better) if I had an outside antenna. On the ham radio side, I bought a FT-60 and can hit a nearby 70cm repeater, but I definitely want to expand and that will absolutely require an antenna. So as I said in another question I posted earlier about grounding, I'm in the very early stages of *thinking* about putting up a mast and a couple antennas.

If I were to put up a mast that clears the roofline of my house and put something like the Comet HVU-8 at the top of the mast, how much vertical separation would I need if I also wanted to put up a Diamond D130J discone for my scanners hanging off the same mast? Honestly I don't think I care of the discone is below the roofline; I'm thinking that an outside antenna a few feet up has got to be better than what I have now.

I know I saw the HVU-8 referred to as a "child's toy" yesterday but it's all about compromises, right? My primary interest right now is VHF/UHF, but if I'm going to put up an antenna it makes sense to pick something that does "OK" on HF rather than putting up a 2m/70cm antenna. I don't ever forsee myself putting up a huge tower or running line-wire antennas across the back yard. Even this idea is subject to approval by the local "homeowner's association", if you get my meaning!

So back to the question ... is what I'm proposing feasible? If so, how far apart should the two antennas be?

 

[K4RBT]

The QST article on this antenna was pretty informative about what it takes to tune this antenna. If it requires moving whatever they call all of the hubs in small amounts, I would expect anything metallic nearby might detune it. It has been a lot of years since college and the semester on antennas. Microwave I can remember well. Have you thought about a Steppr Crankr, it is ground mounted. I have decided to go this route as I need a temporary antenna here and can easily moved when I do.
Also, you have to consider the scanner's leakage that goes back up the feedline. Will close proximity couple that signal to another antenna?

 

[popnokick]

I don't ever forsee myself putting up a huge tower or running line-wire antennas across the back yard. Even this idea is subject to approval by the local "homeowner's association", if you get my meaning!

Homeowner's association? That Comet HVU-8 is going to be a lot more visible... and draw a lot more attention... than a nearly invisible End-Fed Halfwave (EFHW) or Off-Center Dipole (OCFD) wire running from a high location on the house out to a distant support (tree or other support). And either will work FAR better than the gimmick vertical. My HF antennas have always been wires and sometimes my XYL will ask, "I thought you put up a ham antenna?" I'll reply, "I did. Come outside I'll show you." Then I point from over her shoulder up into the air and say, "See it?" Sometimes she'll say, "Oh... now I do." More often, "No... but I believe you."

 

[sallen07]

Homeowner's association?

Did you miss the quote marks?

I have no interest in climbing up on my roof and running a wire out to a tree. I'm sure it would work better, but that's just not in the plan, at least not right now. Plus I'd still need something for 2m/70cm, right? And trust me ... a wire would be seen by the "homeowners association" too.

I appreciate the feedback though. Like I said in my initial post, I'm in the "starting to think about doing something" phase, so if it turns out this is a totally bad idea I will drop it.

So perhaps a follow-up question. If I wanted to put up a discone (for scanning) and a dual band antenna for 2m/70cm, would that change the answer as far as putting them on the same mast?

 

[Ubbe]

If I were to put up a mast that clears the roofline of my house and put something like the Comet HVU-8 at the top of the mast, how much vertical separation would I need if I also wanted to put up a Diamond D130J discone for my scanners hanging off the same mast?

A discone are immune to anything directly below it but above and to its sides are like any other antenna. The bigger distance the better it is, but 3ft are probably enough. It could also work with 2ft but 1ft are too close. The closer to a metallic object the more it could shade the radiosignal from that direction.

A vertical antenna using ground plane elements also do not care much from what is below it so it will be the top element of the D130 that dictates the vertical distance to the Comet top antenna and the horisontal elements of the discone dictates the distance to the mast pole and the discones lower vertical elements distance to the metal pole dictates how much of the radiosignal that will be obscured from that direction.

/Ubbe

 

[W5lz]

The quick-n-dirty answer to that how far apart thing is... as far as is -practical-. Further than that is better but may not be practical.