"Elegant" Antenna DIY Design Questions - HF/VHF/UHF

[kingshootr]

After a looooong hiatus from scanning, I just dove into the RTL-SDR pool. My house is apparently a type of SCIF (block walls, low-e windows, single story) so inside antennas just aren't working. I am set on installing an outdoor antenna. Here is where I have to put it:







My main interests, in order of want, is: Police and Fire/Aviation/Public Safety/Municipal Communications/CB/FRS. I intend to figure out trunking with SDR eventually.

I am not a fan of the size and cumbersome nature of discones. I saw this Moonraker design and it's what I'd really like to do, if it actually works. I can't find a single online independent review of it though.



Questions:

1] Does a steel plate (16"-24" dia) under it add anything to it's receiving ability?

2] The way all these antennas are screwed into a single hub with one coax connection to the scanner - is that a problem or no?

3] If it is, would having 2/3 independent antennae mounted as closely as these, running into a duplexer/triplexer, then to the scanner be a better option, or no difference, or worse? Or, spaced 12" apart +/- on said 24" plate (ideally a 16" plate.) Recommendations for these type of antennas?

If the above is "so far, so good", I'd be looking at mobile, magnet mount, roof top type antennas tuned to each desired frequencies.

4] It would not be taller/above the roof peak - about 12-14ft off the ground. No association to worry about, just how hard the missus will roll her eyes... All houses in the neighborhood are also single story so no house obstructions, (besides roofs.) Airport = 20miles. Public Safety = Unknown, but I'm in an urban area so I have to reason there are plenty of antennas in the area. Is this a waste of time with these conditions?

Thanks for letting me post all this gibberish lol. And thanks in advance for any guidance.

 

[KevinC]

I'm not endorsing that antenna at all, but mine works surprisingly well for VHF and UHF.

 

[iMONITOR]

Maybe consider mounting your antenna on top of the shed instead of the house roof.

You're not planning on transmitting CB on that antenna, right?

 

[popnokick]

Regardless of the antenna you end up using, get it up HIGHER above the roofline. You can do this with what's usually called an "eave mount" or "gable end mount". It's a very simple setup of two crossbars to hold a TV mast or fence top rail post with your antenna on top. To avoid strain on the eave, keep the mast length to 10 ft or less. But that will still get you well above the roofline. And it looks like your neighbor has mounted a TV antenna with an eave mount (way in bground of your pic). You'll need to use some more coax to go along under the eave and around the corner to whichever is the closest gable end. Here is what a gable mount looks like -
https://www.amazon.com/Channel-Mast...ocphy=9059193&hvtargid=pla-319935015285&psc=1

 

[kingshootr]

I'm not endorsing that antenna at all, but mine works surprising well for VHF and UHF.

I'll take your word for it lol. I'm cool with real people/users giving their opinions on a board like this. (The "super moderator" tag helps too.)

Maybe consider mounting your antenna on top of the shed instead of the house roof.

You're not planning on transmitting CB on that antenna, right?

No, no transmitting of any kind, just listening. I was wondering about the shed - as a place to mount it. As a hobbyist welder, fabbing up a sturdy mount is a walk in the park.

Let's say I put the Moonraker's base about 36" above the peak of the shed roof, would it need any kind of ground plane under it?

For a 30ft coax run, with a terminus of a SMA-Male, what coax or conglomeration of parts would be recommended for this installation?

 

[kingshootr]

Regardless of the antenna you end up using, get it up HIGHER above the roofline. You can do this with what's usually called an "eave mount" or "gable end mount".

Good bad or otherwise, I don't have any eaves on my house.

 

[popnokick]

Good bad or otherwise, I don't have any eaves on my house.

View attachment 144704

Gee.... all your neighbors do ;-) Oh well... back to the shed (which DOES have an eave / gable on each end). Hmmm....

 

[kingshootr]

Doh - wasn't thinking...

 

[mmckenna]

Let's say I put the Moonraker's base about 36" above the peak of the shed roof, would it need any kind of ground plane under it?

Yes. 1/4 wave radius at your lowest frequency. VHF, so around 18" radius ground plane will give the antenna what it is looking for.

That's as easy as some 18" lengths of brazing rod. Be sure you consider wind load….

For a 30ft coax run, with a terminus of a SMA-Male, what coax or conglomeration of parts would be recommended for this installation?

That antenna already has 13 feet of coax, so that'll probably get you down your mast. Extend it with something like LMR-200, which is small enough that it's easy to route into your home. You could go larger, but for 30 foot run of cable, you won't see a huge difference.


As for that antenna, I'm suspicious of its design. I think you could do better, but it would cost more.

 

[KevinC]

As for that antenna, I'm suspicious of its design. I think you could do better, but it would cost more.

I was leery as well, but as I said it works surprisingly well. I equate it to "more metal in the air" syndrome.

The way I originally tested it was using weather channels and a weak UHF IFB channel. Swapped back and forth between several other wide-band mobiles and it was equal to or better than all of them. I can't vouch for 7/800 performance as I didn't test that.

But as I said, I'm not endorsing it as that would positively backfire on me.

 

[mmckenna]

I was leery as well, but as I said it works surprisingly well. I equate it to "more metal in the air" syndrome.

The way I originally tested it was using weather channels and a weak UHF IFB channel. Swapped back and forth between several other wide-band mobiles and it was equal to or better than all of them. I can't vouch for 7/800 performance as I didn't test that.

But as I said, I'm not endorsing it as that would positively backfire on me.

Any corrosion? I just see a lot of places for water to collect.

 

[KevinC]

Any corrosion? I just see a lot of places for water to collect.

No, but I don't use it mobile any longer. I only used it a couple of months mobile while I was waiting on my new company vehicle (old one got totaled and then COVID delayed a replacement), after that I went back to permanent mounts...aren't you proud of me?

 

[kingshootr]

Save for the occasional monsoon's - the good old Arizona desert will keep most corrosion at bay .

 

[mmckenna]

No, but I don't use it mobile any longer. I only used it a couple of months mobile while I was waiting on my new company vehicle (old one got totaled and then COVID delayed a replacement), after that I went back to permanent mounts...aren't you proud of me?

I'm proud of you, Super Moderator!

 

[mmckenna]

Save for the occasional monsoon's - the good old Arizona desert will keep most corrosion at bay .

I suspect you are correct.

 

[KevinC]

I'm proud of you, Super Moderator!

Thanks, I ♥ Ø!

 

[RFI-EMI-GUY]

I would go with your second choice. Why? Because your utility meter and the ground rod appear to be very close by. You need to ground the antenna, mast and coax (via a lightning protector) to that common ground point. It is your best option to have an effective ground, reduced electrical noise induced into your system. There are many discussions about grounding and bonding on RR if you have more questions, you can look at what has been suggested. One important point, when adding your ground wire #12 or larger to the existing rod, use a clamp to add your wire to the rod or a clamp to add your wire to the existing bare solid ground from the meter can. Never disconnect the ground rod or wire from your meter can, even temporarily.

 

[RFI-EMI-GUY]

I'm not endorsing that antenna at all, but mine works surprisingly well for VHF and UHF.

It is essentially a fan dipole, a kooky one, but to be honest it is a proven concept that HF folks endorse. It would need to be attached to the supporting pipe in such a way that the pipe provides an effective counterpoise. Some radials might help.

There is always the discone, though the low VHF performance is a concern. But a discone is simple to clamp to a pipe.

 

[kingshootr]

Filled the morning by starting on the roof mount. Handy to have access to scrap steel and an almost ability to fabricate.

It's going to go on one end of the sheds peaked roof. It's a Tuff Shed and all 2x4 and heavy plywood - I don't thing it'll be a problem when I thru-bolt the mount.

Got as far as welding the mast on, then had to tap out - 110F is my limit.










I'll finish it up this weekend. The antenna, coax, etc will be here by then.

 

[mmckenna]

Very nice! That's a great solution.

I've welded up a few mounts in the past, but never for a sloped roof like that. Nice job.