Antenna Questions

[WSGI548]

So I have currently been using an UV5G plus a UT72G stuck to a pizza pan on the end of an extension pole at about 12ft high. This has worked ok for simplex to a buddy about 3 miles away, as well as hitting a couple repeaters, though a little scratchy on the farther repeater(30miles +/-). Kind of a pain to set up, but it works. I currently set it up and down when I want to goof around.
 

I am wanting to start upgrading things a little with the ultimate goal being a base, probably 25 watt, lmr400, and a better antenna. Due to how my house is, shallow backyard with overhead power lines directly over the back fence, I was looking at doing an umbrella base with an extension pole so I can raise and lower when not in use. I  live in the desert, so no trees, most houses 1 story, but high winds during the year.

So my question is primarily about antennas. I understand dbi vs dbd and gain, but what, if any, is the difference between a base (ie: Comet Ca-GMRS) vs a nmo mobile (MXTA26) with a ground radial adapter. I ask because it seems like the base/repeater style antennas are heavy and large , vs the mobile antennas are light and slim. I was concerned about 2-3 lbs antenna on a 16-20 ft extension pole vs a 1/2 lb mobile, thinking about wind load, or am I over thinking this. If all else is equal, is there a difference between a 6 dbi Base antenna vs a 6 dbi Mobile antenna?

 

Any help or insight is appreciated!

 

(sorry if this has been asked before. I tried searching, but didn’t find much)

[SteveShannon]

17 minutes ago, LeoG said:

If you want to give me coordinates, antenna heights and radio power I'll throw it in there to see what it spits out.  Also how you think you are receiving each other R9 R7 R5 etc so I can play around to see if I can get that approx signal strength.

Here’s the best I can do, sorry. I’ve never been there. 
http://www.macpassradio.com/mprg/boulder/

[LeoG]

[SteveShannon]

2 minutes ago, LeoG said:

Thanks for your work. Just one small correction: This is on 440 MHz 

[LeoG]

Oh that'll kill it....

 

[LeoG]

50% reliability brings it to 0.20µV

[SteveShannon]

11 minutes ago, LeoG said:

50% reliability brings it to 0.20µV

Thanks again for doing this.  
This first picture is looking in the direction of the Boulder  Hill Repeater.  

The second picture is of the cabin. The cabin is in what’s referred to as The Boulder Batholith.  The ground is full of these granite boulders. I like it.

[LeoG]

That site you linked me to had GPS coordinates on it, made it pretty easy.

[WSEZ864]

9 hours ago, SteveShannon said:

I think @WSGI548 is probably right about the signal reflecting from something. There’s an old iron transmission line going through the park. There’s are a couple cell towers. There’s granite mountains on either side of the park. Radio is magic sometimes. 
Even more astonishing is the fact that I can use the Boulder Hill DMR 70 cm repeater from my cabin. It’s much further north and with more mountains between it and me. I don’t have coordinates, but I can give you the website and you could approximate the location. I haven’t tried, but I suspect that these programs will predict failure. 

Knife-edge refraction?

[SteveShannon]

2 hours ago, WSEZ864 said:

Knife-edge refraction?

I wouldn’t think so; there’s no knife edge type of topography between me and my friend’s house.  But there are definitely features that would support reflections.

[LeoG]

As much as they say UHF doesn't reflect well, in some cases it does.  I have an area that has a big building I think the signal reflects off of because the signal is in the shadow of a hill and I shouldn't get it.  But right in front of that building I can contact my repeater with an HT and if I move off to either side of the building I can't.  On top of it I'm shadowed by a tall brick building that should degrade the signal even more.

 

Like you said, radio can be magic.

[SteveShannon]

Agreed.  I didn’t know “they” said it didn’t, but UHF (and higher frequencies) reflects very well from some materials, just not from the ionosphere. Passive reflectors are common for microwaves. The mountains in my area are fairly rich in minerals. Butte’s nickname for a century has been “The Richest Hill on Earth” due to the mining activity around here. Whether those minerals contribute to the possibility of UHF reflecting I don’t know, but they don’t seem to retard reflections.

[LeoG]

That website mentioned linked repeaters.  Maybe you are getting a signal from one of those and not the direct line from the actual site.

[SteveShannon]

14 minutes ago, LeoG said:

That website mentioned linked repeaters.  Maybe you are getting a signal from one of those and not the direct line from the actual site.

Nope, unfortunately not. The others are also programmed into my radio. The frequencies are all different. That’s the closest of the linked repeaters (since Butte/Red Mountain is down). The one in Butte is off the air until we get the electrical service replaced. 

[LeoG]

Had to ask.

[SteveShannon]

5 minutes ago, LeoG said:

Had to ask.

Absolutely.  Sometimes I miss the most obvious things. 

[WSGI548]

I am gonna slap my head and say… Doh!!! 

It didn’t click yesterday, but you are in Butte which means your basin is chock full of copper containing rock. I would think has to have an effect on signal, but I am not sure what mechanism.

Hmm, gonna poke around and see if I can find anything on that.

[SteveShannon]

7 minutes ago, WSGI548 said:

I am gonna slap my head and say… Doh!!! 

It didn’t click yesterday, but you are in Butte which means your basin is chock full of copper containing rock. I would think has to have an effect on signal, but I am not sure what mechanism.

Hmm, gonna poke around and see if I can find anything on that.

If nothing else it should make a helluva ground plane!

[LeoG]

Maybe just ground conduction and propagation of the waveform.

[AdmiralCochrane]

Possibly, but doubtful

 

In Washington DC at the entrance to the Naval Observatory, you can reliably hit the Davidsonville UHF repeater at the old NIKE base property.  There are places closer to the Davidsonville side of DC where you can't make the same contact. You definitely do not have line of sight at street level. Must be the buildings there working like a funnel to channel the rf back and forth. 

[WRTC928]

On 2/7/2025 at 5:02 PM, AdmiralCochrane said:

Possibly, but doubtful

 

In Washington DC at the entrance to the Naval Observatory, you can reliably hit the Davidsonville UHF repeater at the old NIKE base property.  There are places closer to the Davidsonville side of DC where you can't make the same contact. You definitely do not have line of sight at street level. Must be the buildings there working like a funnel to channel the rf back and forth. 

Radio waves do weird stuff. There used to be a GMRS repeater about 25 miles northeast of me. From the back yard, I could always work it with a 5 watt HT and sometimes could even do it from inside the house. From the driveway, I couldn't hit it with a 20 watt mobile and an antenna on the vehicle roof. The only thing in between is my house. It's made of 6" logs, but I wouldn't think that would make that much difference. 

[GrouserPad]

I can’t hit repeaters 10 miles from me but I can hit a couple others that are 25+. I can talk to my north/northwest but talking south/southeast is impossible. Those Appalachian foothills are a bugger. Seems to me 462 mhz doesn’t work as well in the woods as 27mhz