Measuring RF Output power on CB radios - Servicing CB radio on a shoestring budget pt2
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- Опубліковано 6 вер 2024
- Richard Shireby (UK) discusses & demonstrates the use of cheap test equipment to measure the RF power output on UK legal cb radio equipment & shows the use of an ammeter either built into a power supply or applied externally to a cheap power supply.
Demonstration shows customers Fidelity 1000 CB radio repair now doing 3W rather than the 500mW it came in for repair generating.
Apologies for poor continuity between day 1 initial recording & day 2 finishing this video. The radio came in doing 500mW, & got a faulty part changed so it then produced 2W....I recorded the first bit in the audio workshop. Next day I went into the RF workshop to record pt2 & found Mr Chippie had finished the faulty radio with a full retune, so it was then doing 2.9W. I wasn't expecting that, but hadn't told him that the Fidelity 1000 repair was part of my video!
This is a good series, many of us know the theory but seeing it put to use in very basic, practical form, drives the lesson home. Thank-you.
Great Video, I always learn something from the knowledge you share, Thank you.
Thank you for sharing your knowledge I am learning alot! Cheers from Canada
Hello Canada. You will only learn about FM from me!
Richard (UK)
Excellent explanation vid
love this series
Very good video.👌
Thanks for another helpful video
which Marconi test set do you use?Ive just recently purchased a 2955 and im very pleased with it.
It's 2951 late version - we have three benches with them on. I also have a bench with a Quartzlock 282 on the bench mehind me & a Schlumberger 4040.
When I was at Nottingham radio (for 16 years), they had three 2955B test sets. I was disappointed with the lag between making adjustments on the radio I was working on & what the test set was reading. When I was at Compass Communications in Bradford later on, they had a Marconi 2951, a couple of IFR test sets, a Motorola one & a Marconi 2955A. I fell in love with the speed I could get results with the 2951. Back then (in the 90's) I had a Farnell TTS520/SSG520 combo test set. When I left Compass to be solely here, I bought the 2951 test sets from various instrument supplier.
Richard, G0OJF, UK
@@ukfmcbradioservicingTango21 the 2951 is a nice bit of kit...looks nice and straight forward to use..i missed out on a 4040 a while back....outbid by 50p🤣
They don't use power meter around here either.
they run their CB radio in to their linear and they key up and adjust their radio drive so the power supply amp meter shows 20amp, that's 100w you know..
you can imagine how many radios and linears have gone bang..!!
and some of these are licenced (used loosely) Amateurs.
are there any cheap watt meters that will actually measure pep power. i bought a astatic 302-pdc2 and it seems useless for measuring actually swing power .essentially only idle transmit power and does not show what it really puts out when modulating, in theory you should get 4x your dead key BUT thats only if the radio is set properly. . so from a deadkey only how do you actually know????
also , for modern radios, just curious what is the efficiency of transmit power in comparison to input power , for example of the radio is drawing 30 watts from [clamp amp meter x power supply voltage] how much of that is actually transmist power, im familiar with car audio amp types with class ab amps being 60% effcient and class d being 90+% effcient, but not sure how effcient these are. .
one last question if you dont mind,
if you have a higher end uni-t true rms meter ac dc clamp meter is possible to read the power. on the out put? i know ohms laws is ohms law so in theory if i can get at least 2 readings i in theory should be able calculate rms from the coac out it, was thinking volts and clamp amps but not sure. . sorry for all the questions , super new to the hobby but also an electrical mcgiver so trying to take what generically know and apply it to my new found hobby
Many Thanks, Mike
Mike, I get the impression you are not in the UK. This channel only covers UK FM CB radio servicing. I'm using a Marconi radio test set. As the test set (and me) are not involved with SSB, the power meter is not PEP.
I looked up the Astatic SWR/Power meter you mentioned. It's a generic meter available in different brands, made in China & aimed at the AM/FM CB radio user, not SSB. With FM, the transmit power always remain the same whether the carrier is modulated or not.
We don't measure power input to a CB FM transmitter ever in the UK. I will say though that the average 4W radio draws 1.3A on transmit at 13.8V.
It seems you are intersted in SSB. All your answers are in the ARRL handbook.
Richard, G0OJF, UK
Good video,
Might be more helpful to know what part was actually replaced in the afore mentioned repair? And how that part was discovered to be faulty
This video is about using a cheap CB power/SWR meter, a cheap power supply, a homemade dummy load and a £2.99 multimeter. The video compares the results on a 1981 Fidelity 1000 UK CB radio doing just under 3W on our laboratory standard Marconi test set with the cheap meters mentioned above. I'm trying to illustrate a cheap way to get valid results for people not wanting/able to spend thousands on test gear. The customer's radio repair will be on a preceding video. We've covered the Fidelity CB1000 & many other UK sets from 1981 that use the same Great (Taiwan) GT848, GT858 & GT868 chassis, many times. I can always cover it again if you want!
Richard, G0OJF, UK
For me I would not do this test, because I can't clearly see how the wires are connected.
Patch lead from the aerial socket of the radio under test to gthe SWR/Power meter. Dummy load into the 'ant' socket of the SWR/pwr meter.
Richard
Hey. I have a small anytalk mini CB radio that claims 4w/8w on low/high power. It draws about 0.25A receive, 1.5A on AM on low power and 2.35A on AM on high power. All on a 13.8v input. How do I calculate the actual rf power? If I use a similar ratio of the total power over rf power of your case ( 11w/3w=3.65) I'm getting 5.7W/8.9W on low/high, do you think that approximation is somewhat accurate? Thanks!!
Pedro, I can only comment on UK legal CB radios, which is what this channel is about. I've never heard of the model you mention & I know of no countries where 8W is legal. That said the power consumption sounds right for the stated output, but again you are talking AM, whereas my training & expertise is FM, which draws less TX current. There is no formula for a relationship to input/output power as it depends on transmitter efficiency. Most 1980's UK radios will draw approx 1A on TX for 4W output making a 12W current consumption for 4W output. Latest models are much less efficient, mainly drawing approx 1.6A for 4W output, so about 20W consumption. The only way to check RF power output is with a quality RF power meter & dummy load. I did a video on this some years ago which is still on youtube. Bear in mind some CB type power meters (such as made by zetagi who also make illegal amplifiers) are wildly inaccurate and may well show a 4W output as 8!
Richard, UK
You said it was doing 2 watts at the start and then said the meter was approaching 3 watts?
continuity.....it got repaired in between takes...done over two days!
What are u hooked up to???
In what respect? Radio is connected to a 13.8V power suppky. Radio is cinnected to the power/SWR meter via the coaxial socket with a short PL259 to PL259 patch lead & the SWE/Power meter has a dummy load connected to it's 'aerial' socket.
Richard, G0OJF, UK
I have the same
Look after it. There aren't many "hobby" type worth having!
Richard
Mr.Chippy ?
Mr Chippie works here & that's his CB handle. His first name is Richard, the same as mine which is confusing for people when he's here !
Richard
@@ukfmcbradioservicingTango21 Ah !😁👍🏼