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)

[BoxCar]

16 hours ago, WSGI548 said:

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)

Base station antennas will have wind load information as it is critical in many installations. It may not be readily available on a retailer's site, but the manufacturer will list it in their brochures for the product.

Yes, there is a difference between a mobile and base antenna. The radiation patterns will most likely vary with the base having a more defined pattern closer toward the horizon. The antenna length also comes into play as most mobiles are base loaded while base antennas tend to be center loaded.

[GrouserPad]

548, that is awesome improvised setup. Props to you for getting on the air. Crutches and all  

[SteveShannon]

On 2/2/2025 at 3:37 PM, WSGI548 said:

If all else is equal, is there a difference between a 6 dbi Base antenna vs a 6 dbi Mobile antenna?

6 dBi is 6 dBi, but with the base antenna you usually have a larger radiator and need less inductance. Higher inductance causes steeper troughs and narrower dips in SWR (called high Q). That means that SWR might be lower across a wider range of frequencies. Also, a larger radiator is usually better than a smaller radiator, if it's tuned correctly, because it has more area to gather RF and because it sticks further up. 

But in actuality, you might never notice a difference. If what you have works for you, I don't think I would change it.

And I agree with @GrouserPad, nice setup!

[WSGI548]

Thanks guys!

It does work pretty well, but is more of a “lets see what I got that will work before we ask the wife for more money for nicer setup”.  
It was definitely an inexpensive way to get a HT some more range. Luckily I am at about 600ft asl but the big repeater is 30 miles away at 8600asl so I can clear the mountains between me and it(about 3000-3500). I will probably go to an umbrella base with a 16-24foot extension pole, maybe with something like a Comet 2x4sr on top. That would give me an easy 4-7 feet taller, but still maintain a fairly light antenna on top. Then I need to decide whether I want a 25w, or 40-50w mobile, but paying 3-4 times the price for about 10% more signal kind turns me off.

Here is the plot for the big repeater I can hit on 5w. I am the blue pin. But this repeater has huge range. We heard a guy last weekend hit it with a 7 element yagi and 50watts iirc from N. Las Vegas, about 110 miles away!! He was scratchy, but readable.

[GrouserPad]

Can you enlighten me as to what app that is showing your “radio path study” ? Looks cool. 

[SteveShannon]

2 minutes ago, GrouserPad said:

Can you enlighten me as to what app that is showing your “radio path study” ? Looks cool. 

It’s a website called scadacore.com. The tool is RF Line of Sight.  https://www.scadacore.com/tools/rf-path/rf-line-of-sight/
 

[GrouserPad]

6 minutes ago, SteveShannon said:

It’s a website called scadacore.com. The tool is RF Line of Sight.  https://www.scadacore.com/tools/rf-path/rf-line-of-sight/
 

Nice! After messing with it on my cell I think I’ll have to fiddle with it on a home computer. The site is hard to navigate with an iPhone. 

[WRYZ926]

The Comet 2x4SR is an excellent multi band mobile antenna. Since you said that you can get into that repeater with an HT then yes going to 20/25 watt radio will improve things. Stepping up to a 40/50 watt radio will definitely improve things.

I have a repeater that is about 50-55 miles away that I can get into with a 20 watt radio but the other people hear a lot of static on my transmission. Everyone can hear me clearly when I use a 50 watt radio.

Basically you have to quadruple the power output to notice any big difference.

I am still going to suggest going with the Comet CA-GMRS for a few reasons. One is that it is light enough at only 2 pounds. Second, it has a wind load of 135 mph. And you can also get rid of the pizza pan that will definitely act as a sail in high winds.

The CA-GMRS is lists at 5.5 dBi which is 3.4 dBd. The 2x4SR is listed at 6.2 dBi ( 4.1 dBd). Plus you would still have to use a metal pan for your ground plane which is a wind sail.

I can't tell in your photo if your roof is fairly flat or has a ridge. Getting your antenna up some more and going with a mobile radio will improve performance for you.

[SteveShannon]

19 minutes ago, GrouserPad said:

Nice! After messing with it on my cell I think I’ll have to fiddle with it on a home computer. The site is hard to navigate with an iPhone. 

It’s a very good tool, but while line of sight is great for vhf and uhf radio work, it’s not absolute.  For instance, here’s how it analyzed the path between my friend’s house and my cabin.  He and I can communicate via 2 meter simplex, but according to the chart we shouldn’t expect to:

[WSEZ864]

The Scadacore site is interesting, but without antenna height input, I don't think it's as accurate as it could be.

NVM, I just figured out how to input antenna heights.

Edited February 5 by WSEZ864
Correction

[LeoG]

On 2/5/2025 at 10:07 AM, SteveShannon said:

It’s a very good tool, but while line of sight is great for vhf and uhf radio work, it’s not absolute.  For instance, here’s how it analyzed the path between my friend’s house and my cabin.  He and I can communicate via 2 meter simplex, but according to the chart we shouldn’t expect to:

You have your antennas set to 1 meter.  Are you both HTs?

[LeoG]

I also use the Radio Mobile Online calculator.  It's much more complex but gives more information.  You do have to figure out how to set it up.  Keep the required reliability up toward the high end or it'll tell you everything will work.  I keep mine at 99.85% and it's reasonably accurate.  It doesn't account for trees which can be a major blockage of UHF so you have to think about that yourself.  You have to sign up for an account to use it.

https://www.ve2dbe.com/rmonline_s.asp

 

[SteveShannon]

14 minutes ago, LeoG said:

You have your antennas set to 1 meter.  Are you both HTs?

Mine is. His is probably 7 meters above ground, but if you look at the topography there are probably 10 kilometers of intervening granite that is as much as 500 feet higher than the “line of sight“ between my cabin and his house. 

[LeoG]

Yep, just noticed it's 300' of mountains.

 

Maybe try it in Radio Mobile, they have a frequency input that might show you it can reach.

[SteveShannon]

18 minutes ago, LeoG said:

Yep, just noticed it's 300' of mountains.

 

Maybe try it in Radio Mobile, they have a frequency input that might show you it can reach.

I know it reaches. My point was simply that if you looked at nothing other that the line of sight tool in scadacore you wouldn’t expect to be able to communicate on either VHF or UHF. 

[LeoG]

Can you tell me what the green location Longitude is please?  I wanted to plot it.  And wattage of your transmitters would help too.

[SteveShannon]

4 hours ago, LeoG said:

Can you tell me what the green location Longitude is please?  I wanted to plot it.  And wattage of your transmitters would help too.

My radio was a typical dual band handheld, 5 watts. 
Here’s the coordinates of my cabin. It won’t exactly match the coordinates from before; I just picked them on the map approximately.

46.13057° N, 112.39271° W

 

[WSGI548]

I wonder if some of your being able to talk to him is due to being on 2m and the granite. Especially since it looks like you are broadcasting kind of down a valley and those ridge lines are almost parallel. Still learning in case I want to get my Technician, but I think I read vhf has a little more bounce than uhf. So much to learn

[SteveShannon]

Just now, WSGI548 said:

I wonder if some of your being able to talk to him is due to being on 2m and the granite. Especially since it looks like you are broadcasting kind of down a valley and those ridge lines are almost parallel. Still learning in case I want to get my Technician, but I think I read vhf has a little more bounce than uhf. So much to learn

I think it probably is. 

[LeoG]

I put your friend as a 50w transmitter and 7 meters of 7.2dbi gain antenna and you as the receiver with and HT

 

[SteveShannon]

Thanks!  He was probably running at 20 watts, but I doubt that makes a huge difference. 

[LeoG]

20 watts brings the signal down to 0.07µV from 0.11µV

 

Don't know what the sensitivity of those radios are but this program seems to say you can't communicate either....  And yet.

[LeoG]

Bringing the reliability down to 96% the signal gets to 0.51µV which is plenty of signal.  I accidentally did 462MHz and it was 0.00µV

[SteveShannon]

8 minutes ago, LeoG said:

20 watts brings the signal down to 0.07µV from 0.11µV

 

Don't know what the sensitivity of those radios are but this program seems to say you can't communicate either....  And yet.

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. 

[LeoG]

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.