Mobile Unit Wattage

[WROZ437]

I’m sure this is not the first time this has come up but searching for terms like “watt,” “power,” “mobile,” etc. yields many many results on a radio forum. I apologize if this has already been beaten to death and I appreciate any insight.

The focus of my questions is that I am considering upgrading my mobile unit. I currently have a Midland MXT275. I’ve gotten the bug a little, so to speak, so I need to decide what general direction I am going. The first step is determining the most appropriate power level for a mobile unit. I would normally assume more watts is better, but maybe that’s not always the case. Some of the less powerful radios have appeal due to their form factor or specific features when compared to higher power units. A prime example would be a Wouxun KG-XS20G. It’s form factor and features are very appealing, albeit at only 20 watts. 

Considering the primary limitation of GMRS is line of sight, how useful is upgrading a mobile radio from say 15 watts to 50? I mean bigger is always better, right? Bust seriously, if an HT can reach 15+ miles (allegedly) in favorable conditions with good LOS, then what are those “extra” 45 watts of power really doing in a mobile unit? I have also read some concerns over RF exposure. How serious are these concerns when TXing at higher power with mobile units?

 

[OffRoaderX]

You wont notice much difference between say, 20W and 50W in most scenarios, most of the time.  The extra power might help penetrate through buildings and things like that, but, most of the time, on average, there is not a huge, if any difference.

One example: Just recently I was testing a UHF mobile radio (XTL5000 for those interested) operating just above the GMRS frequencies. At about 90 miles, I was able to hit a repeater at 50Watts with a signal of about 3 out of 10 on the receiving end.  Bumping the power up to 110W, made no audible difference in my signal strength or quality.  

[BoxCar]

Tim,

Good question but the answer isn't easy as there are more things to consider besides wattage. The key piece to distance is the antenna. Figure your antenna radiates in a pattern that could be described as a beachball with the top and bottom squished. Add gain to the antenna and the beachball just gets flatter and bigger around in the middle. The second piece to your antenna is height, The higher it's mounted on your vehicle, the better as height means the horizon is now further away. Your signal doesn't bend to follow the earth, it reaches the horizon and keeps going straight out. More power just means more signal is reaching the horizon and going off into the ether. Your 15 watts will travel less distance than say 20, 25 or even 50W but once it hits the horizon the extra power doesn't do anything.

The other thing your antenna does is listen to incoming signals, so again height is important as the area covered is a larger diameter. Here, wattage becomes a factor. Signals lose strength the further they travel so a stronger signal as in higher wattage means you can be further apart. Receiving is dependent on the radio itself and its sensitivity. A HT can receive a lot further than it can transmit so I could hear somebody but not be able to talk because my signal isn't strong enough at their receiver. To sum up, a good balance for a mobile rig is the 15 to 25W radio. It will transmit a good signal to the horizon and comfortably reach most of the stations it receives.

[WROZ437]

1 hour ago, OffRoaderX said:

You wont notice much difference between say, 20W and 50W in most scenarios, most of the time.  The extra power might help penetrate through buildings and things like that, but, most of the time, on average, there is not a huge, if any difference.

One example: Just recently I was testing a UHF mobile radio (XTL5000 for those interested) operating just above the GMRS frequencies. At about 90 miles, I was able to hit a repeater at 50Watts with a signal of about 3 out of 10 on the receiving end.  Bumping the power up to 110W, made no audible difference in my signal strength or quality.  

Thanks! Not gonna lie, your video review of the XS20G is what has me interested in that particular radio. I really want to like the stuff offered by Midland but as I go down the rabbit hole I don’t like what I am discovering.

54 minutes ago, BoxCar said:

Tim,

Good question but the answer isn't easy as there are more things to consider besides wattage. The key piece to distance is the antenna. Figure your antenna radiates in a pattern that could be described as a beachball with the top and bottom squished. Add gain to the antenna and the beachball just gets flatter and bigger around in the middle. The second piece to your antenna is height, The higher it's mounted on your vehicle, the better as height means the horizon is now further away. Your signal doesn't bend to follow the earth, it reaches the horizon and keeps going straight out. More power just means more signal is reaching the horizon and going off into the ether. Your 15 watts will travel less distance than say 20, 25 or even 50W but once it hits the horizon the extra power doesn't do anything.

The other thing your antenna does is listen to incoming signals, so again height is important as the area covered is a larger diameter. Here, wattage becomes a factor. Signals lose strength the further they travel so a stronger signal as in higher wattage means you can be further apart. Receiving is dependent on the radio itself and its sensitivity. A HT can receive a lot further than it can transmit so I could hear somebody but not be able to talk because my signal isn't strong enough at their receiver. To sum up, a good balance for a mobile rig is the 15 to 25W radio. It will transmit a good signal to the horizon and comfortably reach most of the stations it receives.

Thanks for the reply! I am glad I am not totally out in left field on this one! For now I am going to focus on polishing up the installation of my MXT275. I’m still playing around with where and how I have my antenna mounted. The MXT275 is leaving me wanting for more, as far as features go, and maybe power too, but I don’t know if I need to go all in on a full 50W radio with the tradeoffs I would have to make on mounting and such. 

[mbrun]

@WROZ437 your getting good advice hear. You only need as much power as you need to reach the parties you trying to communicate with, and no more. As has been said, antenna and antenna height are more impactful that raw power. A 1-watt radio connected to a well placed antenna will outperform a 50-watt radio with a low poorly placed antenna. A shift from 5 to 50 watts will push through some obstacles a little more, your effective real-world usable distance will only increase slightly. So there is nothing wrong with 50, but also nothing wrong with 15 or 25 either.

Personally, on my base and mobile radios I frequently operate at mid and low power until or unless I need the added power to improve my audio level to a station I am communicating with, if they are receiving a low signal from me. I am not on high-power all the time.


Michael
WRHS965
KE8PLM

[gortex2]

I have yet to find a reason to upgrade my MTX275. I have never not been able to communicate with other Jeeps on the trail nor not able to hit a repeater that I should be able to. As said your not going to gain a ton by going up in power. Antenna is most critical point of any radio. I guess in the end what is the reason you think you need to upgrade ? 

[PACNWComms]

7 hours ago, BoxCar said:

Good question but the answer isn't easy as there are more things to consider besides wattage. The key piece to distance is the antenna. Figure your antenna radiates in a pattern that could be described as a beachball with the top and bottom squished. Add gain to the antenna and the beachball just gets flatter and bigger around in the middle.

What applies to ships at sea also applies to vehicles on the ground. Many years ago, after working on vehicle mounted radios for the military, I went to work for the oil industry, and radios aboard a fleet of ships. Well antenna gain issue cropped up often, as many think more gain means more "amplification" of receive signal, not realizing that it is also the radiation pattern impacting signal as BoxCar mentions. Very often, someone would place a 12 dB gain antenna on a small vessel and it had trouble talking to a larger vessel, even when in line of sight and close in distance.

An isotropic antenna would radiate like a sphere, while a 3dB gain antenna may radiate like a doughnut, 6 db gain antenna like a pancake, a 9 dB antenna like a thick tortilla or naan bread, and a 12 dB antenna like an LP record. So, with a 12 dB gain antenna on a small vessel, and a 0-3 dB gain antenna on a large ship, the only reliable communication (due to height differences between vessels) is when the little one is bobbing around and the radiation (transmit for smaller vessel and receive for larger) match up. This is where height and a 0-6dB antenna are much more useful, as they both have transmit and receive patterns that can reach other stations. Power is also an issue, as more power in a more focused radiation pattern can mean more distance. Cars and fixed radio stations are impacted the same way. 

When it comes to wattage and a mobile radio, Part 90 radios in use by public safety, commercial use, and hobby use are often limited to about 50 watts. Motorola, Vertex, Icom, Kenwood, mobiles are often 25/40/50 watts. Attached is a lab kit for Radio over Internet Protocol, with a Motorola XPR4550 UHF 40 watt mobile shown. I used Motorola mobiles for GMRS, with my CDM1550LS+ at 50 watts. GMRS radios usually max out around 50 watts too. Radiation exposure specifications will usually specify 6 foot or so (sometimes less) of separation between people and antennas in the UHF range at 50 watts. 50 watts mobile, with RG-58, and the shorter run in a vehicle than up a high mounted fixed antenna will get you ten to twenty miles, depending on terrain and local conditions. I myself usually run about 10 to 20 watts mobile and have no problem hearing people, hitting repeaters ten miles away, and transmitting back. The radio tops out at 10 watts, my RG-58 cable run is about twelve feet, and I have a decent antenna on the trunk which acts as a good ground plane. If what you have works, then let that itch go to a basestation, or a handheld that can be taken when not in your vehicle. Glad to see someone else get further into this......GMRS has taken off over the past few years for sure. 

[WROZ437]

3 hours ago, gortex2 said:

I guess in the end what is the reason you think you need to upgrade ? 

I think it’s more that I bought the MXT115 before really doing a whole lot of research. The MXT115 was inexpensive enough that I didn’t sweat the purchase too much. After the fact I started diving a little deeper and learned about some of the shortcomings of Midland stuff like no wideband, limited features, etc. The radio will do everything I need it to do. 

I’ll heed the advice of you, @PACNWComms, and the others who replied above and stick with what I have for now. Even with that being the case, all the replies in this thread have help me gain more understanding. Maybe I’ll snag a decent handheld at some point….

 

[wayoverthere]

Think of it as a not too expensive learning tool. While it is a bit feature limited, if it does what you need it to then no need for more. If not, it helps show what features are needed in the next one.

I have one as well. It served it's purpose, and it's still on the shelf as a backup now.

Power wise, on a good antenna, 15 watts can do quite well. I tend to run the ham mobile on mid power (15 watts), and had no problem getting a "loud and clear" report on a repeater 60ish miles way on a vhf 1/4 wave, while for another closer 70cm, I just run low (5 watts). In the other car, a 5 watt handheld into an external antenna is enough to get by.

[WyoJoe]

30 minutes ago, WROZ437 said:

I think it’s more that I bought the MXT115 before really doing a whole lot of research. The MXT115 was inexpensive enough that I didn’t sweat the purchase too much. After the fact I started diving a little deeper and learned about some of the shortcomings of Midland stuff like no wideband, limited features, etc. The radio will do everything I need it to do. 

I’ll heed the advice of you, @PACNWComms, and the others who replied above and stick with what I have for now. Even with that being the case, all the replies in this thread have help me gain more understanding. Maybe I’ll snag a decent handheld at some point….

 

In the case of the MXT115, if/when you are looking for more features and functions, an inexpensive upgrade is the Anytone AT779UV / Radioddity DB-20G / Retevis RA25 radio (each of these is the same as the others). For about $100, you get another small radio that puts out ~20W, offers narrow and wideband, repeater capable, and offers UHF and VHF receive capability. It can also be reconfigured so it will work on the 2m and 70cm ham bands, should you ever wish to pursue, or if you already have, a ham license. It also has a small, but useful, color display.

On top of all that, it even comes with a "Fun" button on it! What more could you ask for? Okay, the "Fun" button is actually the "Function" button, but the word Function didn't fit on the small button.

[Coffeemaker]

My 5 to 5.5 watt Wouxun (ocean) handheld can carry on a conversation with an Atlanta area repeater 110 miles away, with a little static.  It can hit an East Tn repeater 72 miles away clearly.  Other than a few dozen trees around me on my mountain property, both are unobstructed line of sight transmissions.  With UHF it isn't all about power. 

[MichaelLAX]

What is your elevation?

Which model Wouxun?

[AdmiralCochrane]

I love the FUN button

[WyoJoe]

9 hours ago, Coffeemaker said:

My 5 to 5.5 watt Wouxun (ocean) handheld can carry on a conversation with an Atlanta area repeater 110 miles away, with a little static.

This makes me wonder, does the radio talk to the repeater about people? People talk about radios, so turnabout would be fair play!

[Over2U]

The (old) Midland MicroMobile radio in my Land Rover has a maximum output of only five (5) watts, but works fine for vehicle-to-vehicle use in a convoy setting.

[Coffeemaker]

20 hours ago, MichaelLAX said:

What is your elevation?

Which model Wouxun?

I'm at 2350 and both repeaters are about 3300 feet. 

I've used each repeater with an 805 and a 905.  Mostly the 805. 

[Coffeemaker]

12 hours ago, WyoJoe said:

This makes me wonder, does the radio talk to the repeater about people? People talk about radios, so turnabout would be fair play!

ROTFL!!  Too bad I forgot to eavesdrop. 

[WRUA262]

Question: I have a Radioditty DB-25G that I am using as a base station coupled with a 30A power supply, using LMR400 coax (35FT) with a GMRS J-pole antenna (in the attic) from KB9VR. This is a 25 watt radio, but the most I have been able to get on high power to a repeater (462.675) is about 13 Watts. Where am I loosing those 10-12 watts? Through the coax? I have the end of the cable looped 4-5 times about a foot away from the antenna itself. SWR is 1.2 with the the Farsometer 2000 showing FW: 12.94W and RW: 0.121W. Those 10-12 watts seem to be disappearing.

On the 5 watt frequencies, it transmits at exactly 5W.

Any ideas what would help find/recover the missing watts?

[BoxCar]

Are you certain the DB-25 is putting out full power? Also, measure the power from the radio at the antenna connector. You could have a bad connector at either end of the cable.

[marcspaz]

Where are you measuring the power? At the radio or at the antenna side? How long is the coax between the radio and the meter? Is the cable between the radio and the meter also LMR400?  How long are your power wires? What gauge are the wires? Are there any connectors on the power wires between the power supply and the radio. What method did you use to connect the power cables to the power supply? (Lugs, power poles, screw-downs, etc.)

 

The more information the better. 

[WRUA262]

2 minutes ago, BoxCar said:

Are you certain the DB-25 is putting out full power? Also, measure the power from the radio at the antenna connector. You could have a bad connector at either end of the cable.

As far as I know, yes. The radio is set to HIGH. The SWR reading was taken between the radio and the antenna. I'll try taking another reading at the end of the coax next to the antenna. I've rechecked the coax fittings, both ends are tight. Since it's an attic antenna install, no need to worry about water encroachment or weather issues. I'll also try ferrite couplers and see if those help as the coil of coax by the antenna might not be doing its job.

[WRUA262]

1 minute ago, marcspaz said:

Where are you measuring the power? At the radio or at the antenna side? How long is the coax between the radio and the meter? Is the cable between the radio and the meter also LMR400?  How long are your power wires? What gauge are the wires? Are there any connectors on the power wires between the power supply and the radio. What method did you use to connect the power cables to the power supply? (Lugs, power poles, screw-downs, etc.)

 

The more information the better. 

Measuring power between the radio and the coax cable (radio side). The coax is 35FT long. But you might have hit on something - the pigtail between the meter and the radio. Its not the same size as the LRM400. Its quite small/thin in comparison. Maybe it can't put through all the watts to the meter due to the pigtail size?

The power wires between the radio and power supply are about 18" long or so. The gauge is what came with the radio. The only thing in between the radio and power supply is an in-line fuse. Power is connected through screw-downs.

[wayoverthere]

I'd be curious what numbers would look like into a dummy load rather than into the antenna. I'd also be curious to test how much difference in numbers a short pigtail (12"-18" ) really makes in the numbers.

For reference, I did some testing on 70cm awhile back with a vertex standard radio (rated 45 watts out on high), the 17 ft of unlabeled cable that came with a Midland mount, and 35 ft of abr400. Measured at the radio, with coax and comet gp1 attached, I saw 43 watts either way. Measuring at the antenna end, the Midland cable showed 23 watts, while twice the length of abr400 showed 35 watts at the antenna.

I want to say it was spot on 45 with a dummy load at the radio.

[marcspaz]

7 hours ago, WRUA262 said:

Measuring power between the radio and the coax cable (radio side). The coax is 35FT long. But you might have hit on something - the pigtail between the meter and the radio. Its not the same size as the LRM400. Its quite small/thin in comparison. Maybe it can't put through all the watts to the meter due to the pigtail size?

The power wires between the radio and power supply are about 18" long or so. The gauge is what came with the radio. The only thing in between the radio and power supply is an in-line fuse. Power is connected through screw-downs.

 

Everything actually sounds good.  I have to agree with a few things that @wayoverthere mentioned about the cable and a dummy load.  Unless the patch cable is some really obscure cable that is incredibly high loss due to a bad connector attachment, etc., the patch cable is likely not it. 

 

I would replace the patch cable with some LMR400 (or equivalent) just as a quick test.  Also, get a dummy load to test with.  I use this one and its pretty good for the price.

https://www.amazon.com/s?k=Mcbazel+Surecom+0014-0156&i=electronics&crid=1PHJLEIZFR33P&sprefix=mcbazel+surecom+0014-0156+%2Celectronics%2C59&ref=nb_sb_noss

 

 

[wayoverthere]

7 minutes ago, marcspaz said:

 

Everything actually sounds good.  I have to agree with a few things that @wayoverthere mentioned about the cable and a dummy load.  Unless the patch cable is some really obscure cable that is incredibly high loss due to a bad connector attachment, etc., the patch cable is likely not it. 

 

I would replace the patch cable with some LMR400 (or equivalent) just as a quick test.  Also, get a dummy load to test with.  I use this one and its pretty good for the price.

https://www.amazon.com/s?k=Mcbazel+Surecom+0014-0156&i=electronics&crid=1PHJLEIZFR33P&sprefix=mcbazel+surecom+0014-0156+%2Celectronics%2C59&ref=nb_sb_noss

 

 

I use the 60 watt version of the Surecom dummy load as well, though I forgot about checking with the dummy load perhaps later/next time. 

Did a little testing though; same abr400, same gp1, same vx4207 and same surecom sw102.  There's now a diplexer after the radio, which it shares with a vx4204 en route to the coax/antenna. all tests were done on an unused 70cm simplex frequency, with 4 different pigtails. Pigtail sat between radio and meter, with diplexer connected to the TX port on the meter.

1. 18" black rg8x - 1.03:1 swr, 48.4 watts
2. 12" Proxicast branded LMR240 - 1.05:1 swr, 49.5 watts
3. 36" grey pigtail, unmarked but listing claims rg8x - 1.02:1 swr, 48.8 watts
4. 6" RG174/u from nanoVNA kit, with SMA-F to PL259 adapters at each end - 1.05:1 swr, 47.5 watts.

Truthfully, not surprised to see a minor effect between cables.

Trying another cable would help reduce the possibility of a bad cable being the issue.  One other thought that hit me was taking a multimeter to that power supply, just to make sure it's putting out what it should be, both current and voltage. 30a (even peak rated) should be more than enough for 25 watts (the vertex and btech show 10-11amps draw on high power), and i'd expect around 5amps for a 25 watt radio.

if both of those check out, i'm leaning toward the radio is the issue.