mobile radio wattage

Snakedoc84 · Jan 27, 2015

Hello,
Wanted to see if I can get some input on something. Got my first SWR/power meter last week, and was messing around with it, tested a buddy of mines base station that has his own private frequency for his farm, and the power reading we got was almost 80 Watts of power. How is this possible if he is only running a 50 watt radio for his base station. The radio is an HYT TM-628H, radio has not been modified in any way. Does this have to do with the way his antenna is tuned? Thoughts? Thanks.

n9mxq · Jan 27, 2015

Is the swr/watt meter for the same band as the radio bring tested?

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ko6jw_2 · Jan 27, 2015

The radio specs show it to have a 50 watt output. The antenna would not affect the power output and certainly not a higher output. A poorly matched antenna might show a lower than normal forward power and significant reflected power. What frequency is the transmitter? What kind of meter? Does the meter cover the frequency range of the transmitter? An HF meter would not read accurately at VHF/UHF frequencies, for example. If you have a dummy load, you could test the power and rule out any antenna issues.

Snakedoc84 · Jan 27, 2015

No i guess its not. Its rated 140-150Mhz and the freq we were testing is 153Mhz. That's probably why then.

Snakedoc84 · Jan 27, 2015

I'm fairly new to the radio world, and didn't think to check that. Guess ill be getting a different SWR meter.

jackj · Jan 27, 2015

Why not get a power meter that can be switched between forward and reflected power? I have an old Bird model 43 watt meter, you buy the slug(s) (elements) that you need for both frequency and power range. I'm not sure that meter is still available but similar meters are.

ko6jw_2 · Jan 27, 2015

I don't think 153Mhz is far enough outside the meter's range to cause that big an error. Maybe you can find a ham and check it against another transmitter or a known accurate meter. Brand and model number?

I've been using a Diamond SX-600 for years with good results. It covers from 1.6Mhz to 550Mhz with two separate inputs. Not real cheap, but not as expensive as a Bird.

Snakedoc84 · Jan 27, 2015

Its a Nissei RS-40. Ok, I will check into the kind your using. Thanks for all the help.

ko6jw_2 · Jan 27, 2015

Yes, you need a meter that can measure forward and reverse power to really work with antennas. Also a more precise meter scale would be helpful.

A dummy load is quite important for isolating transmitters from feed line and antenna problems. Also useful for testing coax.

ramal121 · Jan 27, 2015

ko6jw_2 said:
Yes, you need a meter that can measure forward and reverse power to really work with antennas.

A SWR meter is fine. You can interpolate between the two without any problems. The problem is how accurate your meter is.

The wattmeter you state you have has really mixed reviews on it's accuracy on eham. I have both a Bird 43 and a Thruline and even though they are 10 times the price or better of the meter you have, I still would not hold them to be an accurate measure of transmit power. All I want is a reasonable reading of forward to reflective power (or SWR) for the bandwidth of the device. Those meters rely on voltage readings across a standard 50 ohm impedance. Once the antenna or feedline vary from 50 ohms, as Forrest says, you never know what you're gonna get.

Now if I had a nice Agilent power meter (which I don't) that uses a thermocouple to detect power and cost thousands I might be more comfortable in the power reading from a transmitter.

So if I hook up my Bird to a radio rated at 35 watts and I get between 30 and 40 on the meter, I don't sweat it that the transmit is close to specs and any adjustment will probably not even be noticed.

So even though your wattmeter seems way out of whack, fan it and just use the ratio of forward to reflective (SWR) to determine antenna performance hoping it is somewhat correct.

freddaniel · Feb 2, 2015

Also be aware on SWR or power meters that measure using RF voltage, it is common for any reflected power from the antenna to be added to the forward power, thereby displaying a false reading. The first issue is to know you have little reflected power before relying upon your forward reading.

prcguy · Feb 2, 2015

Bird wattmeters are not that expensive used, somewhere between $100 and $150 will get you a good working unit and low/medium power VHF/UHF slugs are about $35 each. You can also find 50ohm loads up to the 60w range and 1GHz for about $15 on Ebay.
prcguy

WA0CBW · Feb 2, 2015

As "freddaniel" said with a 50 watt radio measuring 80 watts what was the reflected power? It was probably 30 watts. This is an indication of very high SWR. 80 watts forward minus 30 watts reflected equals 50 watts. This is what you might expect using a good wattmeter (i.e. Bird).
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mobile radio wattage

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Lots and lots of watts

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