2m/440/GMRS Mobile Antennas Needed

[marcspaz]

7 hours ago, Whistlepig said:

Thanks for the reply.

 

One more question. DO you think mounting a 7900 on a bed rail close to the cab or doing something like a SSB1 on a third brake light mount would end being much different in TX/RX?

 

I would keep any antenna as far away from the cab as possible. Depending on power and distance to the antenna, there are RF exposure concerns. Also, the antenna either on the bed rail or hood, next to the cab, will impact SWR and the radiation pattern. 

 

I mounted mine in the back driver's side corner. I think there is no comparison between the 7900 and the SSB1. It doesn't matter where the SSB1 is, unless it's 100 feet in the air, it's not going to outperform the 7900.

[WRTC928]

6 hours ago, Whistlepig said:

Thanks for the reply.

 

One more question. DO you think mounting a 7900 on a bed rail close to the cab or doing something like a SSB1 on a third brake light mount would end being much different in TX/RX?

I have my SG7900 on the bed rail at the very back driver's side in a stake pocket mount. It works quite well with essentially no ground plane. Obviously, your results may not be the same; however, DX Engineering claims that it works well without a ground plane, so apparently my situation isn't unique.

[AdmiralCochrane]

9 hours ago, marcspaz said:

 

I would keep any antenna as far away from the cab as possible. Depending on power and distance to the antenna, there are RF exposure concerns.

Exactly how much power are you pushing???

[marcspaz]

8 minutes ago, AdmiralCochrane said:

Exactly how much power are you pushing???

 

800w on HF (depending on the band), 300w+ on VHF, and 115w on UHF.

[Whistlepig]

7 hours ago, marcspaz said:

 

800w on HF (depending on the band), 300w+ on VHF, and 115w on UHF.

You think 300w is enough to worry about over exposure through the cab?

[marcspaz]

1 hour ago, Whistlepig said:

You think 300w is enough to worry about over exposure through the cab?

 

RF exposure calculations put the minimum safe distance at 11.5 feet.  In some vehicles, you can get a little closer, due to the steel and glass offering some minor RF shielding.  However, think about how well an HT works inside a vehicle cab.  Now think about people in vehicles like Jeeps, with zero shielding from the cab.

You are not "safe" at 3 feet just because the 300w radiator is on the other side of the window.  Are you going to die right away?  No.  Are you slowing cooking cells with RF heat, which over time can cause serious health issues, including burns (depending on how close) and cancer?  Absolutely.

[dosw]

20 hours ago, Whistlepig said:

I understand the ground plane issues I am dealing with but do not have much of a choice, drilling a hole in the center of the cab is not going to happen and a magnet mount will not work out good for me.

If it goes on the third break light it is going to have to be a shorter antenna, my truck is 7'2" tall so a 5 footer will be way top much up there. This is the issue I am in trying to figure out, a taller antenna on the bed rail or a shorted on third break light....in my mind the shorter on the break light mount would do better but not totally sure and hate the make a $400 gamble on it.

I recall that if you read back in the thread you will see I posted about the Larson NMO 2/70 which is a no-ground-plane antenna. That's possibly a better choice for your mounting options. 

[Lscott]

23 hours ago, marcspaz said:

 

800w on HF (depending on the band), 300w+ on VHF, and 115w on UHF.

What power amps are you using and or is that the raw power output of the radio on VHF and UHF?

[marcspaz]

51 minutes ago, Lscott said:

What power amps are you using and or is that the raw power output of the radio on VHF and UHF?

 

My VHF amp is a Mirage/MFJ B-320-G.  It was originally 200w (198w measured at 150 MHz), but the PA blew, so I replaced it with a custom final circuit that puts out 300w FM (319w measured).  The UHF is straight out the back of my XTL5000.

[Lscott]

1 minute ago, marcspaz said:

 

My VHF amp is a Mirage/MFJ B-320-G.  It was originally 200w (198w measured at 150 MHz), but the PA blew, so I replaced it with a custom final circuit that puts out 300w FM (319w measured).  The UHF is straight out the back of my XTL5000.

That’s cool. I know at one time MIRAGE sold a 300 watt VHF amp.

[marcspaz]

20 minutes ago, Lscott said:

That’s cool. I know at one time MIRAGE sold a 300 watt VHF amp.

 

Yeah... I wish I could have gotten a factory 300w model.  I think toward the end, the biggest one was only 150w-160w.  Even at 200w, it worked fantastic for the money.

[WRTC928]

14 hours ago, marcspaz said:

 

My VHF amp is a Mirage/MFJ B-320-G.  It was originally 200w (198w measured at 150 MHz), but the PA blew, so I replaced it with a custom final circuit that puts out 300w FM (319w measured).  The UHF is straight out the back of my XTL5000.

So, serious question. Not being snarky. What do you do on VHF/UHF that you need 300 watts for? I can hit any repeater within reasonable distance with 50. If I'm so far away that I can't reach it with 50 watts, the terrain has usually become the limiting factor. 

[marcspaz]

12 hours ago, WRTC928 said:

So, serious question. Not being snarky. What do you do on VHF/UHF that you need 300 watts for? I can hit any repeater within reasonable distance with 50. If I'm so far away that I can't reach it with 50 watts, the terrain has usually become the limiting factor. 

 

That is a very reasonable question.  I'm actually glad you asked. Honestly.

So, first and foremost, I believe in the principle of using only the amount of power needed for reliable communications.  If we can have clear communications with 0.5w and increasing power to 1w or 5w makes no improvement in reliability, then I will simply use the 0.5w.  That said, I am a bit of  horsepower junkie, with several of my cars having north of 700rwhp.  Some of that personality bleeds over to radio, where I want as much power as I can afford.  LOL

As far as piratical application, I originally got my VHF amplifier because myself and some of my friends were doing a lot of mobile simplex in areas that are highly congested with RF noise.  In some places we had less than a mile of range.  We needed more than 40 or 50 watts due to the desense cause by the environmental noise. We all decided to buy amps for the mobiles.  What we found was, not only were we able to get over the RF interference in town, but when we go into the rural areas and using SSB, it boosted our simplex range from about 8 miles, to as far as 28 miles. 

When I am participating in VHF/UHF contests, it helps tremendously when I get up to 4400-4500 feet.  I have worked other higher powered stations as far out as 200 miles with legit Q5 reports both ways. Again, from a mobile.  No beam or other complex setups.  Just park the Jeep and talk.

Another benefit is, there are some repeaters around the DC metro area that have 150w-200w coming out of the duplexer (300w+ radios).  Before I bought the MFJ amp and the high-power XTL5000, there were a lot of occasions where I could hear the repeater fine, but due to losses on the repeaters receiver path, my weaker signal was not being heard.  With the higher powered mobile capability, my VHF and UHF repeater capability is more properly balanced for the systems I use.

 

Do I drive around pumping 300w/115w all the time?  Nope.  A vast majority of the time I am running about 20w on VHF and UHF.

[WRTC928]

19 hours ago, marcspaz said:

 

That is a very reasonable question.  I'm actually glad you asked. Honestly.

So, first and foremost, I believe in the principle of using only the amount of power needed for reliable communications.  If we can have clear communications with 0.5w and increasing power to 1w or 5w makes no improvement in reliability, then I will simply use the 0.5w.  That said, I am a bit of  horsepower junkie, with several of my cars having north of 700rwhp.  Some of that personality bleeds over to radio, where I want as much power as I can afford.  LOL

As far as piratical application, I originally got my VHF amplifier because myself and some of my friends were doing a lot of mobile simplex in areas that are highly congested with RF noise.  In some places we had less than a mile of range.  We needed more than 40 or 50 watts due to the desense cause by the environmental noise. We all decided to buy amps for the mobiles.  What we found was, not only were we able to get over the RF interference in town, but when we go into the rural areas and using SSB, it boosted our simplex range from about 8 miles, to as far as 28 miles. 

When I am participating in VHF/UHF contests, it helps tremendously when I get up to 4400-4500 feet.  I have worked other higher powered stations as far out as 200 miles with legit Q5 reports both ways. Again, from a mobile.  No beam or other complex setups.  Just park the Jeep and talk.

Another benefit is, there are some repeaters around the DC metro area that have 150w-200w coming out of the duplexer (300w+ radios).  Before I bought the MFJ amp and the high-power XTL5000, there were a lot of occasions where I could hear the repeater fine, but due to losses on the repeaters receiver path, my weaker signal was not being heard.  With the higher powered mobile capability, my VHF and UHF repeater capability is more properly balanced for the systems I use.

 

Do I drive around pumping 300w/115w all the time?  Nope.  A vast majority of the time I am running about 20w on VHF and UHF.

Okay, that makes sense. Even the "personality" part.  Some of my quirks bleed over into various hobbies as well. Perhaps the reason I've never felt the need for more power is that the airwaves aren't congested in Oklahoma like they are in DC. Even with the two dozen or so ham and GMRS repeaters in the Oklahoma City area, most of the time the airwaves are pretty clear. A few days ago, I talked on GMRS simplex with the base unit/antenna in my house to a guy atop Mount Scott 82 miles away using a mobile. 50 watts on each end punched us through quite clearly. 

I do find myself bumping up power from 20 or so watts to 40-50 for some repeaters in fringe areas, but with a mobile, I hardly ever hear one I can't reach. The base unit in my house is a different story, but I'm using an antenna 45' in the air. There are a couple of pretty distant repeaters I can hear but not talk to . Maybe I could also talk to them if I bumped up the power, but so far, I haven't been highly motivated to do so. I talk regularly on 6 repeaters and occasionally on a couple of others, and for now I'm happy with that.

I'll file your experience away for future reference in case I find myself with similar issues. Thanks for clarifying that for me.

[AdmiralCochrane]

Airwaves around DC aren't that congested either.  Other than drive time and nets, you may go hours without hearing anything on most channels and frequencies.

[marcspaz]

22 hours ago, AdmiralCochrane said:

Airwaves around DC aren't that congested either.  Other than drive time and nets, you may go hours without hearing anything on most channels and frequencies.

 

Yeah, there are definitely peak times, but quiet most of the day.  My problem with noise/interference was with the whole Manassas/Centerville area. There is an insane amount of RF noise from all of the businesses through that area. Most of the time, I would have a 9 s-unit copy on my friends while I'm in Woodbridge, and as they would drive north on 28, I would still have a perfect copy on them, but their radios would get desensed to the point where they couldn't here me at all, until they got north of Dulles. It sucked. And it's still like that for people without amps.

[nokones]

On 12/4/2025 at 1:29 PM, marcspaz said:

 

That is a very reasonable question.  I'm actually glad you asked. Honestly.

So, first and foremost, I believe in the principle of using only the amount of power needed for reliable communications.  If we can have clear communications with 0.5w and increasing power to 1w or 5w makes no improvement in reliability, then I will simply use the 0.5w.  That said, I am a bit of  horsepower junkie, with several of my cars having north of 700rwhp.  Some of that personality bleeds over to radio, where I want as much power as I can afford.  LOL

As far as piratical application, I originally got my VHF amplifier because myself and some of my friends were doing a lot of mobile simplex in areas that are highly congested with RF noise.  In some places we had less than a mile of range.  We needed more than 40 or 50 watts due to the desense cause by the environmental noise. We all decided to buy amps for the mobiles.  What we found was, not only were we able to get over the RF interference in town, but when we go into the rural areas and using SSB, it boosted our simplex range from about 8 miles, to as far as 28 miles. 

When I am participating in VHF/UHF contests, it helps tremendously when I get up to 4400-4500 feet.  I have worked other higher powered stations as far out as 200 miles with legit Q5 reports both ways. Again, from a mobile.  No beam or other complex setups.  Just park the Jeep and talk.

Another benefit is, there are some repeaters around the DC metro area that have 150w-200w coming out of the duplexer (300w+ radios).  Before I bought t MFJ amp and the high-power XTL5000, there were a lot of occasions where I could hear the repeater fine, but due to losses on the repeaters receiver path, my weaker signal was not being heard.  With the higher powered mobile capability, my VHF and UHF repeater capability is more properly balanced for the systems I use.

 

Do I drive around pumping 300w/115w all the time?  Nope.  A vast majority of the time I am running about 20w on VHF and UHF.

RWHP - now, we're talking my language.

 

 

[marcspaz]

2 hours ago, nokones said:

RWHP - now, we're talking my language.

 

 

 

That's hot! When I get home, I'll share a couple pics of my track car and a couple of my street cars.