My 50w Radio Doesn't Make 50w. Why?

[marcspaz]

 

This question has been coming up a lot lately...   "My 50w Radio Doesn't Make 50w.  Why?" 

 

I figured I would post quick highlights of the more common items that lead to low power.  This is just a list of a few items.  If anyone would like a bit more detail, just ask and myself or one of our seasoned operators will be happy to help with further explanation.

 

One of the most common issues that will prevent you from reaching a full 50 watts is the manufacturer.  They have to have their device certified by the FCC in order to be sold in the US.  The radio needs to be sold in the configuration as tested and certified.  If the radio or any subsequent builds tested exceed 50w, even if it's not intentional due to something like component tolerances, the manufacturer will either not get or lose their certification. 

 

To avoid risk of losing certification, when the radios are designed, they are designed to operate at much less power.  I know for a fact that many popular brands target 46w, so they can round-up to 50w for advertising.  However, manufacturing tolerances allow for +/- 4w.  So, a properly running new radio under the absolute best conditions could make as much as 50w or as little as 42w.  Again, only under perfect conditions.

 

Those perfect conditions are typically 13.8vdc "at the radio" (not at the power source), almost unmeasurable losses due to test gear insertion, a proper dummy load, and being on the channel/frequency that the manufacturer centered up the transmit power to.

 

The following issues are just a few that will lead to less than ideal conditions.

 - Not testing on the channel/frequency that the manufacturer tuned for max performance.

- The power source is too low.

 - Power cables are too long, lending to too much voltage loss at the radio.

 - The power cables are too thin for the current draw and length of the power cables, lending to too much voltage loss at the radio.

 - Power cables have connections that are crimped instead of soldered.

 - Corrosion at the battery connectors or other connectors in the power lines.

 - Improper grounding of the radio.

 - Improper grounding of the antenna.

 - A bad or poor performing antenna.

 - Bad or poor performing antenna cables.

 - RF interference from something in the vehicle that is close to the radio, causing improper performance.

 

There can be more than this, but in my decades of experience, these are the top problems I have seen.  Below is a video showing the difference between my amateur radio on my bench vs installed in my Jeep.  Even mine isn't perfect because I wanted to use the factory auxiliary switches, as well as Power Pole connectors for easy removal, and I don't mind losing a few watts compared to the convenience.

 

 

[marcspaz]

@Rican  Hopefully this helps.  Even if BuyTwoWayRadios.Com is willing to exchange the radio, I doubt that will resolve your issue.  It's possible, but resolving any issues you find in this list are more likely going to bring you improvement over what you have currently.

[Rican]

13 minutes ago, marcspaz said:

@Rican  Hopefully this helps.  Even if BuyTwoWayRadios.Com is willing to exchange the radio, I doubt that will resolve your issue.  It's possible, but resolving any issues you find in this list are more likely going to bring you improvement over what you have currently.

Thanks, I hope they can help!

[JohnE]

same thing in the commercial world. Difference being that anything out of the box "should" be checked before it goes out the door. I can site many examples of things like this. Big M SLR programed power 55W- reality 49.5-50 on a calibrated Bird watt meter into a calibrated service monitor. Kenwood mobiles out of the box are for the most part pretty on but do require minor tuning depending on Freq, generally the higher you go the lower the power. AT 450 you might get 48-49 but T-band 42-45 just as an example.

[SteveShannon]

Hopefully Rich will pin this so people see it when they first come to the forums.  It seems to be a pretty frequent question. 

[WRKC935]

OMG is this REALLY a topic of discussion.  The MOST common issue for a radio that is rated for 50 watts NOT doing 50 watts is it's actually NOT generating 50 watts.

The second most common issue is line loss.  And for the love of God, 49.37 watts is not 50???  Are you KIDDING ME?!?!?!?!

This type of stuff is where the lack of ANY sort of testing of knowledge of subject matter to get a license becomes fully apparent. And drives guys that have a heavy back ground in RF systems up the damn wall.

As Mark mentioned, there are a ton of singular reasons that power output can go down from what the spec the manufacture stated as being the 'rated output'.

Any ONE of these can come into play, and it's typically a combination of them that will reduce power output.  And these figures are generated by the designer NOT a test by the manufacture when the radio is built.  And people need to have SOME small understanding of how much effect there is on coverage when you are down to 45 watts from 50 or even 25 vs 50.  Becasue there is NO difference between 50 and 49 at ALL.

Case in point.  I loose 30 watts in my transmit combiner.  So when my repeater is programmed for 50 watts, my power level leaving the building as measured at the surge suppressor at the cable window is 20 watts.  The repeater talks for 30 miles in most directions and is only limited within that circle of coverage by topographical issues.  Meaning I can't get RF to pass through hills, buildings and other structures.  And that is a fact of UHF RF propagation and is consistent with all equipment operating on the frequency range.  Nothing to do with 50 vs 20 watts.  If I increased the power to 200 or even 2000 watts those locations would still be blocked from reception of the signal. 

Something as simple as a 3 foot cable being between the transmitter and the watt meter WILL decrease measured power.   By at least a couple watts at UHF regardless of the cable type.  And even the connectors have loss in them.  So on paper the radio may calculate to have a power output of 50 watts but you will never seen that power level with an accurate meter due to something that simple.

 

Another issue with not measuring the rated power of a radio is the radio and the meter used to measure the power.  Good test equipment is expensive.  A Bird 43 power meter is about 300 bucks new.  The required element for it to work is another 150 bucks.  And that meter is rated for an accuracy of 10 percent of the full scale indication of the element in the meter.  Meaning if the element is 100 watts, that meter can be off as much as 10 watts and STILL be considered within spec. 

You are measuring a 100 dollar radio with a 20 or 30 dollar meter and expect the same level of accuracy.  Yeah Right.  I don't care if the meter has ability to indicate down to the hundredths (.01) of a watt.  It ain't that accurate.  I have a 40K dollar piece of test equipment that is coupled to a 700 dollar power coupler that is all sent off the be certified every year and calibrated.  It ain't THAT accurate.  And if you think that the meter you got from Amazon for 40 bucks is better than my 40K dollar piece of test gear, then YOU are the one living in a dream world and nothing I can say here is gonna change that.  Hell I can make a measurement with what I have, disconnect the cables, reconnect them and they will indicate a difference in power of more than a hundredth of a watt.  And that is just from cable placement and cycling of the connectors.  And YES, ALL RF connectors have a finite number of connects and disconnects before they are deemed 'used up' and have to be replaced.  For microwave testing, the adapters and connectors are rated for between 50 and 100 insertions.  And cost 50 or 100 dollars a piece for a simple N female to SMA male adapter.  And NO you don't check 6 Ghz microwave power levels with a Bird 43 either.  That would be done with a HP watt meter that the POWER sensor is over 1000 dollars and the meter is around 10K.  And the N connector is replaced on those every 2 years during calibration.  Now that is getting into lab grade test equipment, which is NOT something that you are going to be buying from Amazon for 40 bucks.  But it WILL measure accurately down to .01 watts and below depending on the power sensor used.

 

[marcspaz]

56 minutes ago, WRKC935 said:

OMG is this REALLY a topic of discussion.  The MOST common issue for a radio that is rated for 50 watts NOT doing 50 watts is it's actually NOT generating 50 watts.

 

I laughed pretty good on this one. LoL

 

I know it's hard to believe, but I have seen enough people ask this question that I figured I could post it in one spot and just link it. That way I don't have to type it over and over.

 

I know what you mean about the meters, too. I have a Tektronix analyzer sitting on the shelf of my office. $26k when it was new,, a million years ago..  I do like the cheap meters because their good enough for pass/fail, which is all most GMRS operators need.  Plus, if I put screen grabs from the analyzer up, the people who need to know what it says, can't understand what they are looking at.

 

But, yeah... here we are. LoL 

[WRKC935]

On 9/11/2022 at 6:11 PM, marcspaz said:

I know what you mean about the meters, too. I have a Tektronix analyzer sitting on the shelf of my office. $26k when it was new,, a million years ago..  I do like the cheap meters because their good enough for pass/fail, which is all most GMRS operators need.  Plus, if I put screen grabs from the analyzer up, the people who need to know what it says, can't understand what they are looking at.

Oh, I can't agree more.  If you are looking for a relative measurement the cheap meters are great.  And if they are 10% or even 20% accuracy, they are enough to tell you that you are squirting RF out of the radio and the SWR is close or way off.  And I have some of that stuff too.  

I run an Anritsu 412LMR Master and a 50dB Connecticut Microwave 100Mhz to 1Ghz directional coupler for doing high power readings.  And I am expected by both my employer and my main client to check the loss of the cables I am using and do my power calculations with those loss numbers in mind.  In fact the client saw me doing it and when they ask what I was doing and I explained it, they required everyone else in the state to do the same thing.  So my coupler is 50dB down from the actual signal level.  So a 100 watt signal (50dBm) would register at 0dBm without that cable loss but at 800 Mhz that cable has 2.7dB of loss so it's significant, and will through the readings WAY off if not accounted for.  Of course it all got questioned until I connected the 3 thousand dollar Roade and Swartz watt meter up in line as was within 1.5 watts of what I had on the paper for my reading.  At that point they were all happy and rewrote the procedure for doing RF power readings at an RF site. 

Now I don't break all that out to check the SWR on a mobile antenna for a vehicle install.  I use one of my Bird meters for that. And it's MORE than accurate enough to do that work.  

 

And maybe I was a bit harsh on my reply,  but I thought my head was gonna explode when I read that.  Not your answer to it, but that it's a topic even being discussed. But I get a LOT of that.  I had one today, guy was wanting to know why his vehicle repeater was not working when he was driving down the street.  I wanted to tell him because whoever installed it actually did it right.  They are connected to the park neutral switch so they specifically DON'T work when you are in motion.  That's what the mobile radio in the vehicle is for..... the one connected to the VRS (vehicle repeater system) that you talk through when you are on a fire ground and OUT of the vehicle.   I honestly told my boss what was up and to explain that the system is designed that way to keep from causing interference while responding and driving past another working incident where they were also using a VRS to extend their coverage.