Commercial Quality Power Readings

[Seven-Delta-FortyOne]

Is it possible to get accurate RF power output readings from an SWR/directional wattmeter, or is it necessary to use an oscilloscope?

I'm talking about something as accurate as checking a CB for the difference between 3 and 4 watts, as well as testing basic Ham and Commercial gear to verify advertised power specs. I've seen the accuracy on most of these meters described as +/- 10% at full-scale readings.

Are there any that are more accurate?



Delta

 

[mmckenna]

A Bird 43 with calibrated elements/slugs for the frequency/power you are testing connected between the radio and a 50Ω load is usually pretty damn accurate. There are "lab" grade instruments, but going to that level for a CB is kind of overkill.

 

[TLF82]

A Bird watt meter or a Telewave watt meter will get you pretty dang close. If you need exact numbers then a service monitor is the way to go but that involves big money to get your own.

 

[mikewazowski]

Birds are +/- 5% at full scale. Enough for most hobbyists and professional people without spending a fortune.

Even at +/- 10%, it's easy to tell the difference between 3 and 4 watts.

 

[prcguy]

I use an HP power meter and calibrated high power attenuators to check or cal other wattmeters and these power meters are around .5% accuracy. In the 1970s the largest CB mfr in the world used Bird 43 wattmeters to QC and repair CBs, so they are adequate for that. Around 1980 the FCC used a Bird Termaline wattmeter with built in load to check my CB stuff.
prcguy

 

[mmckenna]

A Bird watt meter or a Telewave watt meter will get you pretty dang close. If you need exact numbers then a service monitor is the way to go but that involves big money to get your own.

Caution, the Telewave meters that don't have the slugs are notorious for being off by quite a bit. Fell for that, now I only use my Telewave only as a rough indication of RF power.

 

[Seven-Delta-FortyOne]

Thanks for all the info, guys.

I looked at the Bird and HP meters, they look nice, but they weren't that much more accurate than a Diamond or Daiwa SWR/power meter.

I looking to check my GMRS equipment mostly, with the added bonus of tuning the CB's if I can.


Probably for my (non-commercial) use, a "Ham" type meter will work fine.

Thanks



Delta

 

[WA8ZTZ]

Hams are obsessed with SWR, commercial radio techs not so much.

Hams use SWR meters, commercial radio techs use a Bird 43.

 

[jackj]

I've worked as a communications tech for most of my life and the only watt meter brand I've EVER depended on is Bird. I bought a model 43 and a few slugs when I opened my CB shop and it is the only piece of test equipment I still own from those days. They are not cheap but they will last the rest of your life and maybe even your son's.

 

[TLF82]

Hams are obsessed with SWR, commercial radio techs not so much.

Hams use SWR meters, commercial radio techs use a Bird 43.

Because you can use a Bird to get SWR... Commercial guys care about SWR as well. It's very important. It's just that most of their antennas come tuned for what they are doing to begin with and aren't trying to cover a ton of bandwidth at one time.

 

[WA8ZTZ]

Because you can use a Bird to get SWR... Commercial guys care about SWR as well. It's very important. It's just that most of their antennas come tuned for what they are doing to begin with and aren't trying to cover a ton of bandwidth at one time.

Well, my point was that a commercial guy isn't going to spend all day trying for a perfect 1:1 match.

The customer would gag on the bill.

If the tech reads, say, 25 watts forward on the Bird Thruline and has maybe 1 watt reflected, it probably will be considered good to go.

 

[AK4GA]

I tune for lowest reactance. As long as that comes with something less than 2.0:1, I am happy. I am skeptical of any antenna that will tune to 1:1 exactly.

 

[Seven-Delta-FortyOne]

Thanks for all the help, folks.

I'll probably get the MFJ 884. It covers 1.8-525.

I mostly want to check SWR on a couple mobile GMRS rigs, and see if they are putting out close to their advertised 45 watts. I'll also tune the 980 SSB while I'm at it. I've heard they come from the factory a little low.



Delta

 

[Project25_MASTR]

Thanks for all the help, folks.



I'll probably get the MFJ 884. It covers 1.8-525.



I mostly want to check SWR on a couple mobile GMRS rigs, and see if they are putting out close to their advertised 45 watts. I'll also tune the 980 SSB while I'm at it. I've heard they come from the factory a little low.







Delta

I've had nothing but QC issues from MFJ meters…I don't even use their antenna analyzes.


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[cmdrwill]

I've had nothing but QC issues from MFJ meters…I don't even use their antenna analyzers.

We do not use them anymore either. Sold one I rebuilt, and junked the others.

Using genuine Bird wattmeters.

 

[WA0CBW]

I believe that combination of SWR/Power meter will only read the correct power if connected to a 50 ohm load.
BB

 

[mmckenna]

Keep your eyes open for a used Bird 43 on e-Bay. The actual meter is very basic and not much to it. Short of them getting run over by a train, there isn't much you can't repair on them.

Slugs get a bit pricy, but it sounds like you only need a few. You can find "used" ones on e-Bay if you look.

Like others said, a Bird 43 is the last meter you'll ever need to buy.

 

[KevinC]

I've had nothing but QC issues from MFJ meters…I don't even use their antenna analyzes.


Sent from my iPhone using Tapatalk

I believe people used to say MFJ=Mighty Fine Junk.

 

[cmdrwill]

I believe people used to say MFJ=Mighty Fine Junk.

Some say something else that ends with JUNK.

 

[ElroyJetson]

An oscilloscope is completely and totally the wrong tool for RF power measurements. "Utterly useless for that" is a phrase I would use.

Define "accurate" measurement. Accurate to what percentage?

I no longer have the setup because I no longer need it and sold it for a fair profit, but I used an Agilent E4431B RF power meter with sensor (I forget which one, E series model, anyway) and the setup was calibrated by a cal lab along with the 100 watt 30 dB pass-thru attenuator that was
always incorporated into the system. The entire system was calibrated as a system, and used as a system, and was recalibrated yearly but it received a "special" calibration, being calibrated only from 10 MHz to 1 GHz. I never needed more than that so that kept the cost of calibration down.

It was accurate to, if I remember correctly, 0.1 percent over its calibrated range.


Now as far as opinions go on test equipment, for precision power measurement, Agilent and Rohde & Schwarz are the only names that matter. Bird meters are suitable for field use if they are checked carefully against calibrated standards.

MFJ is adequate for CB and amateur radio but I wouldn't use them for any testing on commercially licensed equipment.

The big thing about using proper calibrated equipment, power meters in particular, is that a lot of radios are not very tolerant of having their output power turned up beyond rated limits. A poorly calibrated power meter could easily be off by as much as 3 dB (I've seen worse) and 3 dB is equivalent to halving, or doubling, power output. Use that meter to set power output on a 5 watt radio and depending on the direction of the error, you might end up with the meter saying 5 watts with actual power output being anywhere between 2.5 watts ( possible range issue complaints) and 10 watts ( if it'll do it, it won't do it for long!) so using an accurate power meter is essential.

Frankly, if you don't have a GOOD and CALIBRATED meter that's still within its calibration period, don't even BOTHER to do a power measurement and adjustment. The measurement error is likely to be more than the amount that the transmitter drifted since it left the factory.