UHF wattage really matter?

[timfrank]

is their really a difference from 15 to 20 to 45 watts out of a 1/4 UHF vehicle grounded antenna? I use a TYT 8600 with 1/2 wave NMO on my SXS to hit local repeater as a cell phone backup out on the trails, now looking at a Midland MTX275 package that comes with a roof mountable magnet antenna. Only looking at this model due to 2013 Rams with console shifter really have no extra dash space. Will I get decent range or should I put a NMO on it for a ground plane?

[Lscott]

IF range was only determined by power then your range varies by the square root of the two powers. For example comparing 45 watts to 15 watts you get:

sqrt(45/15) = 1.73

In other words your range should increase by a factor of 1.73 going to 45 watts verses 15 watts. There are other factors that will conspire to reduce this.

You need to pay attention to the cable between the radio and the antenna mount. The RG-58 cable that’s typical used is fairly lossy at UHF. The loss can be compensated for by using a gain antenna. 

High gain antennas have their issues so they might not be a good fit for your application. If you mainly operate in very hilly or mountainous terrain a simple 1/4 wave antenna likely will work better. For flat open terrain a high gain antenna performs well.

There are a few antennas that require no ground plane allowing more options on mounting locations. Some of the other forum members likely have some good recommendations for this type of antenna.

A few people even keep more that one type in the vehicle and swap them out depending on operating requirements. Maybe a high gain one for use in a convoy while travailing on a highway then a short 1/4 wave for off road use.

[maddogrecurve]

I do not know about UHF but I know that with HF, wattage makes a huge difference!!!!  When i had a little kicker in line, I could talk about 15 miles further to a guy on the way to work than I could without.  The difference in wattage was only about 60 watts, and my antenna was the best (in my opinion) a 102" whip, though I had crappy RG 58 coax on a Tram magnet mount.

I now use the same mount but I swapped coax for my usual RG/8x coax, but no longer run the kicker.

 

I plan on getting a mobile UHF/VHF radio really soon and will see how well I can do with further repeaters, but I also know that I cannot talk to those that I cannot hear!  I may be in the same boat that I am in with my HT!!!

[gortex2]

I run the MTX series in both my jeeps. I have yet to run into an issue with repeaters or simplex. With that said throw the antenna in the trash that comes with it and put a real NMO mount in the vehicle. If the repeaters are good repeaters at good locations you should not have much trouble. 

[BoxCar]

14 hours ago, maddogrecurve said:

I do not know about UHF but I know that with HF, wattage makes a huge difference!!!!  When i had a little kicker in line, I could talk about 15 miles further to a guy on the way to work than I could without.  The difference in wattage was only about 60 watts, and my antenna was the best (in my opinion) a 102" whip, though I had crappy RG 58 coax on a Tram magnet mount.

"I plan on getting a mobile UHF/VHF radio really soon and will see how well I can do with further repeaters, but I also know that I cannot talk to those that I cannot hear!  I may be in the same boat that I am in with my HT!!!

HF "bends" by reflecting from layers in the atmosphere. UHF doesn't reflect so is line of sight to the horizon.

[JeepCrawler98]

36 minutes ago, BoxCar said:

HF "bends" by reflecting from layers in the atmosphere. UHF doesn't reflect so is line of sight to the horizon.

In general it's good to plan on UHF being line of sight for reliability purposes. With that said, VHF and UHF can go beyond what you can see pretty readily. It's not going to bounce off the atmosphere (short of rare atmospheric conditions), but you do have refraction and reflection within the environment.

If you're standing on a perfect marble - yup it's going to go into space like you mention. Same for the most part with rolling hills or paths over sustained topography; it's what you can see for the most part.

Down in my neck of the woods (Tucson), there's a lot of isolated mountain ranges. If you're on the other side of a mountain and the topography is such that the top of the mountain forms a somewhat clean 'knife edge' between you and another station roughly perpendicular to your path; the signal can actually bend over the top pretty easily and you can get a pretty appreciable signal even thought here's a huge mass of rock in your way.

Likewise, UHF can also reflect on large planar-ish surfaces such as rock faces. I have a few repeaters I can hit/hear from Phoenix at my house decently (over in the northern end of Tucson) even though I have a small mountain range in the way. When I point the yagi at Pusch ridge (a large rock face/cliff formation about 15 miles from my location), they actually come in with a solid signal, if I try and point it at the direct path to the repeater, it's nothing but noise. Plotting the path on Google Earth actually revealed that this rock face is at almost a perfect angle to act as a reflector in this direction where both my station and the repeater have line of sight to it, but not between my station and the repeater directly. This has actually proven to be a reliable tool for me for hitting those machines - works every time.

Edited October 22, 2021 by JeepCrawler98

[axorlov]

Exactly how JeepCrawler98 explained: reflection and refraction. This is how I receive off-air TV signal at my home. An this is my experience with mobile<->HT comms over mountain terrain. And this is when wattage starts to matter, because you want power in your reflected scattered signal.

[AdmiralCochrane]

The same reflection and/or refraction occur with a repeater in Maryland working into/out of Washington D.C.   Colocated on the same tower and linked, the repeater owner has both VHF and UHF repeaters.  One would expect the VHF repeater to work better into the heart of the city, but in fact, the UHF repeater has better penetration and users transmitting to the repeaters are heard better on the UHF repeater. 

[Lscott]

On 10/22/2021 at 4:11 PM, JeepCrawler98 said:

In general it's good to plan on UHF being line of sight for reliability purposes. With that said, VHF and UHF can go beyond what you can see pretty readily. It's not going to bounce off the atmosphere (short of rare atmospheric conditions), but you do have refraction and reflection within the environment.

If you're standing on a perfect marble - yup it's going to go into space like you mention. Same for the most part with rolling hills or paths over sustained topography; it's what you can see for the most part.

Down in my neck of the woods (Tucson), there's a lot of isolated mountain ranges. If you're on the other side of a mountain and the topography is such that the top of the mountain forms a somewhat clean 'knife edge' between you and another station roughly perpendicular to your path; the signal can actually bend over the top pretty easily and you can get a pretty appreciable signal even thought here's a huge mass of rock in your way.

Likewise, UHF can also reflect on large planar-ish surfaces such as rock faces. I have a few repeaters I can hit/hear from Phoenix at my house decently (over in the northern end of Tucson) even though I have a small mountain range in the way. When I point the yagi at Pusch ridge (a large rock face/cliff formation about 15 miles from my location), they actually come in with a solid signal, if I try and point it at the direct path to the repeater, it's nothing but noise. Plotting the path on Google Earth actually revealed that this rock face is at almost a perfect angle to act as a reflector in this direction where both my station and the repeater have line of sight to it, but not between my station and the repeater directly. This has actually proven to be a reliable tool for me for hitting those machines - works every time.

This is a good reference on passive repeaters.

https://www.softwright.com/faq/engineering/Catolog 161A - Screen.pdf

Might be a fun experiment to use a small Yagi directional antenna to bounce signals off a local water tower. While not flat it could spread the signals out enough to cover a wide area.