FM Transmitter Watt Measurement

[codenose]

Hello. Could anyone please tell me how I can test the watt output on a unit I bought? I bought a 30 watt FM transmitter and I would like to know if it is transmitting 30 watts. Thank you.

 

[blueroomelectronics]

Don't you need a license for that power of RF transmitter? What frequency does it transmit on? What model is it?

 

[MikeMl]

Spend about $150 on Ebay and buy a used Bird Wattmeter with a 50 W slug for 100MHz.

 

[Sceadwian]

You most defniitly need a license for 30 watts, regardless of what you're doing.

 

[Externet]

Codenose : Any amateur radio operator will very likely have a power meter. Look at roofs by your neighborhood and somewhere you will see antennas and a door to knock. A true amateur radio operator will gladly help you.

Or, if cannot spend for the power meter, connect a 110V ~ 250W light bulb to the RF output; will give you a rough idea by its brilliance.

Miguel

 

[blueroomelectronics]

I would think an amateur radio operator would frown on an unlicensed operator with a 30W transmitter. I wonder if he's trying to jam the drug dealers in his neighborhood's cell phones?

 

[Sceadwian]

30 watts? The cell phone people's lawyers will be knocking on his door inside a week =)

 

[tcmtech]

License is just a piece of paper for the law abiding people to feel justified about having.

In my area there are still a good number of old CB operators with 100 - 1500 watt kicker boosters still around. The few I have personally known over the years have said flat out they dont have any license or care to ever get one.

I have an old 250 watt CB booster and several smaller ones around here some place too!
I never had to get a license to buy them or to use them. I just dont use them long enough to get caught!

 

[unclejed613]

oscilloscope and 50 ohm dummy load, and calculate E²/R. any method not using a dummy load is most likely illegal and may end with a friendly visit from the men in bad suits asking for a $10,000.00 donation.

 

[Sceadwian]

tcmtech, people that use boosters like that are the bane of hams the world over. On a good day, the reflections from that will travel across the entire globe and bleed out lower power local transmitters. And please don't say the solution is for the local guys to get more powerful transmitters =)

 

[Miles Prower]

tcmtech, people that use boosters like that are the bane of hams the world over. On a good day, the reflections from that will travel across the entire globe and bleed out lower power local transmitters. And please don't say the solution is for the local guys to get more powerful transmitters =)

On a good day, the signal from the CB itself could do that. The A Number One problem with those CB linears is that most of them were designed badly, and radiate out of band. Unforch, the FCC is so utterly incompetent (remember, FCC director is a patronage position) that they won't do anything about it. To this day, the US is the only developed nation that does not have an amateur longwave band.

It's not like the Canadians who had the trucks out the day after Audioguru fired up an illegal, milliwatt FM xmtr powered by a 9V battery.

The FCC is too busy monitoring Howard Stern for using bad words to care about anything else. If this new (un)Fairness Doctrine goes through, they'll be even less concerned.

So go ahead: fire up that CB linear.

 

[Hero999]

oscilloscope and 50 ohm dummy load, and calculate E²/R. any method not using a dummy load is most likely illegal and may end with a friendly visit from the men in bad suits asking for a $10,000.00 donation.

I was going to suggest that but what happens if your scope isn't up to the job, i.e. the highest it can go is 2MHz?

Simple, connect a high speed RF diode and a 1nF capacitor across the 50R load and measure the voltage with a DVM. This will give you the peak voltage (minus the rectifier losses) and assuming the waveform is reasonably sinusoidal you should be able to calculate the power.

 

[tcmtech]

I am neither for or against the big transmitters. I have a few and I know people that still use them.
And fortunately for all us prairie dwellers there is loads of open range to hide in!

I do understand the concerns of the ham guys.
but like my buddy said about the times when he was trucking trans continental. (before cell phones)
It was nice to be able to flip a switch at 2 am and talk to your wife while your on the road in Michigan and shes at home in Idaho!
So screw everybody that was in between us, I was feeling lonely that tonight!

I dont think there are that many big CB transmitter guys running any more. Cell phones and commercial business band took care of most of the old school long distance communications.
I haven't hooked up a CB in at least 7 years if not more.

 

[unclejed613]

"reasonably sinusoidal"........ anything but absolutely sinusoidal would be radiating out of band...... which even if the transmitter were licensed, the out of band radiation would be illegal. IIRC the technical standards are rather tight, like -60dbc for harmonics and intermod products. for any industrial uses of RF, like induction heating, the standards are very loose, and in some cases, there are no standards. i worked at a company that made audio equipment, and our next door neighbor made small lots of semiconductors. their induction furnace regularly interfered with our test equipment. repeated calls to the FCC were a waste of time, as the equipment didn't even need licensing. i ended up walking over there and explaining what was happening (it was after all of the calls to the FCC that i found out where the RF was coming from). they gave me a tour of their induction furnace room, and i was able to tell them how to shield the machine and the room. their setup when i saw it was a "rube goldberg" contraption. the exciter chassis sat in a corner of the room with automobile jumper cables going from the output terminals half way across the room to the induction jar, and a surplus vacuum capacitor laying on the table next to it. all open wiring and battery cable hand clamps, and the room was "shielded" with chicken wire stapled to the walls. none of the wire panels were actually connected to each other, and none of it was grounded. a few weeks later they were able to fire it up again with only a few microvolts of radiation detectable in our audio shop (where before it had been a few hundred millivolts).

 

[Externet]

A true amateur radio operator would gladly help and guide the proper use of anyone willing to learn a new technical area, measure the power of the adquiered gadget, or get a technical tutorial.
I sense an overprotective position from many of the posters here about the entity regulating the use of radio transmitters.

The law was not meant to be interpreted but to be obeyed, but the reason to 'control' the use of radio transmissions is to prevent public airwaves to contribute to crime of any sorts.

To be entitled to use any radio transmitter, a license must be had.

The airwave polluters and worst interference makers in the planet are not radiotinkerers nor the illegal radio operators. Are the F****N compact fluorescent light bulbs

Those killed the radio amateur activity. And no entity has moved a finger about it.

And if to operate a radio transmitter you need a license, better the government regulating entity start (yes, sure!) by mandating licenses to ALL CELLULAR TELEPHONE USERS. Those are radio transmitters; in hands of whoever and irresponsable users too, used in illegal activities too, and hard to monitor, and of extreme security danger when misused.

If ever a guy in black knocks at my door about radio transmissions, will get an earful, even if I end in jail. I do not make illegal use of radio, and have a license -no, I have two!-

Miguel
Amateur radio operator -before CFLs-

 

[unclejed613]

the guys in bad suits are just the messenger boys. some radio regulation was initiated to keep everybody from making a total mess of the airwaves, and because radio waves know no borders. however, that said, a lot of radio regulation in the last 30 years is a game of "follow the money". these days it's not a matter of what regulation or licensing makes sense, but what keeps the money flowing in. remember the FCC was investigated by Congress..... why? not because they had done anything wrong or stupid, but because they were behind schedule auctioning off the VHF Analog TV band, and hadn't made enough money.

three things will get you a visit from them, 1) interfere with a "safety of life" service (this one is completely understandable), 2) causing interference to a TV or radio station owned by one of the big conglomerates, or 3) causing any trouble with the multibillion dollar cellular industry.

 

[tcmtech]

I have to agree with Externet on the gross polluters observation. The old boys I know had big CB amplifiers but their over all time use was small.

I work around commercial and industrial equipment a fair amount and I know its not just CFL's that give off loads of RF noise.

Most anything that uses an arc of some sort has a rather large RF noise being generated. Regular fluorescents, HID bulbs, arc welders, plasma cutters.
I've also been around motor VFD units, induction heaters, many switch mode power supplies and any older vehicles or machinery that uses a points and condenser type ignition systems. All of these could easily and often greatly interfere with radio and local TV and computer monitors.

But ultimately the money makers make and enforce the rules we all live by.

 

[unclejed613]

there are people on CB that are a bit over the top..... like the Ch 6 "shootout" ops (are these guys still around?????). a few years ago a magazine did an article about these guys..... one with a mobile rig that required 10 alternators mounted on a frame in his engine compartment to operate.... another that required a diesel generator on a trailer to operate.... one of these "shootout" ops claimed an ERP of 50kW..... i know that when i used to work CB, these shootout ops were on the air 24/7.... you knew when you passed channel 6 by the sudden burst of noise, it was noisier than ch 19, i still use CB from time to time when i go camping up in the mountains. it's a fairly solid comm method in rough terrain, but my friends and i use SSB, and don't spend a lot of time on the air yacking.

 

[Hero999]

Those killed the radio amateur activity. And no entity has moved a finger about it.-

I think the Internet did a better job of killing amateur radio than CFLs or anything else.


Who needs amateur radio to talk to people on the other side of the world when there's forums, email and Skype?

 

[tcmtech]

I think the dam testing and license crap, the generally poor quality of communication, and the overall time, effort and money it took to get anything that worked half way reliable had a big part in its general decline also.

You spend countless hours and loads of money to do what? Talk to strangers with staticy and garbled sound while trying to tune out or filter every background RF noise that is produced by man made or natural phenomenon.

No thanks! Just plug in an X-box or a computer and immerse yourself in something besides the reality that is all around you. No license BS, easy hookup, great sound, plus great video graphics and world wide reach!