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Author Topic: PEP readings on Swan WM-3000  (Read 2104 times)
VE3TMT
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« on: November 15, 2012, 08:10:37 PM »

Recently picked up a Swan WM-3000 PEP meter. If I set the TS940 for 100watts output, the meter on the radio agrees with digital readout on my 993B tuner. The PEP reading on the Swan agrees, if I send a carrier, however when speaking into the mic, the PEP output only shows about 80watts. Could this be due to the characteristics of the mic or is there something out of adjustment in the Swan?
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KA5IPF
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« Reply #1 on: November 15, 2012, 09:11:38 PM »

Could be the meter, could be the radio. Some 940's were limited in SSB power. What is the SN on the radio?

Clif
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VE3TMT
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Posts: 391




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« Reply #2 on: November 16, 2012, 03:02:31 AM »

Hi Clif,

Radio is a 9,01x,xxx unit.

Max
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VE3TMT
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« Reply #3 on: November 16, 2012, 04:40:43 AM »

But I do wonder if it has an IF unit from an earlier model. It also suffers from the S-meter slam on power down, that supposedly was fixed in this range of units.
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N4NYY
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« Reply #4 on: November 16, 2012, 05:00:44 AM »

Check the resistors out on that meter. Do not know how old it is, but it could have carbons that are way out and giving you bad readings. I rebuilt a VTVM because the readings were off. Went with 1% metal film. I took a look at the schematic, and there is nothing to it. There isn't much there. Clif is the Kenwood expert, so I would go with what he says first.
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VE3TMT
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« Reply #5 on: November 16, 2012, 05:14:29 AM »

If I key the radio for 100 watts in FSK, regardless whether the meter is in RMS or PEP mode, it shows roughly the same amount, close to 100W mark.

If I modulate in SSB it shows about 80W on the Swan. If I switch it to RMS mode it only shows around 20-30W so I know the PEP circuit is working.

I guess what I am wondering is this, if the meter shows 100W in PEP mode on a carrier, should it not show 100W PEP on SSB? I may have to try another microphone and see if there is a difference. The radio also has the balanced modulator tap so I tried the mic through my preamp that way and it gave the same PEP readings on SSB. So before I dabble inside, which I don't want to do, I will try another microphone.

Look at mic station on QRZ, you can understand why I don't want to touch the radio, too much work to get at it!!
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KE3WD
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« Reply #6 on: November 16, 2012, 06:57:24 AM »

That sounds about right.  ALC may be kicking in, but the 20W difference in the reading would not be enough of a concern for me to go inside this rig at all. 

Are you taking the measurement into a known good Dummy Load?  Antenna may not be "perfect" measuring situation. 

Try Whistling into mic for nice steady tone, if you haven't done so already. 

Type of mic and its audio passband might also come into play here as well as settings on the radio. 

Don't expect to be able to modulate the full 100W with mic in sideband mode, don't expect ANY wattmeter to be super-accurate either, there are design reasons for that, check the specifications for the particular wattmeter, specifically those "+/-" accuracy figures. 

And don't sweat a "missing" 20 watts.  We're not using a linear scale here. 

Nobody at the other end is going to be able to tell that slight difference. 


73
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VE3TMT
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« Reply #7 on: November 16, 2012, 07:01:12 AM »

Thanks guys,

I'll leave it as is. I appreciate the information.

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KA5IPF
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« Reply #8 on: November 16, 2012, 08:08:39 AM »

Your SN is not in the range of "low SSB power" so you should be good there. If you can whistle up to 100w in SSB your meter is not working as a true PEP meter, either thru design or component failure.

Clif
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VE3TMT
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« Reply #9 on: November 16, 2012, 08:46:58 AM »

Hi Clif,

Yeah if I whistle solidly, and at my age it's tough, I can get 100 or so watts on the meter. But talking at a normal voice is lower, but a lot higher than RMS reading, so I would think the PEP part of the meter is working??

On the 940, I reach ALC peak on the 940's meter (end of red zone) at about 9 o'clock on the mic gain. Does this sound about right?

Max
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N4NYY
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« Reply #10 on: November 16, 2012, 09:53:06 AM »

Hi Clif,

Yeah if I whistle solidly, and at my age it's tough, I can get 100 or so watts on the meter. But talking at a normal voice is lower, but a lot higher than RMS reading, so I would think the PEP part of the meter is working??

On the 940, I reach ALC peak on the 940's meter (end of red zone) at about 9 o'clock on the mic gain. Does this sound about right?

Max

That sounds normal. I have an FT-950 and rarely get 100W peaks from talking. I would think I am closer to 50-75W. When I whistle, then I reach the 100W level.
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KA5IPF
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« Reply #11 on: November 16, 2012, 08:48:18 PM »

Hi Clif,

Yeah if I whistle solidly, and at my age it's tough, I can get 100 or so watts on the meter. But talking at a normal voice is lower, but a lot higher than RMS reading, so I would think the PEP part of the meter is working??

On the 940, I reach ALC peak on the 940's meter (end of red zone) at about 9 o'clock on the mic gain. Does this sound about right?

Max

That's about right. Most peak from 9-1 o'clock.

If the meter is true PEP it doesn't matter about the voice as it will register and show the peaks on the meter. From what you are saying it is a quasi-peak reading meter. The wattmeter I use will show whatever the peak is at the moment but when i recall the peak it will show the highest reading.

I don't depend on voice as I use a 2 tone generator for a constant level. With a 940 set for 105w CW power out on 20m when using SSB and the 2 tone generator the wattmeter in avg mode it will show from 35-50w depending on the alignment of the carrier oscillators however peak mode will show ~115w. Both times the measurements are back up by the 'scope also hooked up. Although not calibrated in watts the peaks are higher in SSB than CW.

Besides, who gives a rats patootie. Can you communicate and be heard? If so the power doesn't matter. I thought our hobby was about communicating, building, experimenting, and furthuring the knowledge base not comparing s-meter readings.

Soap box put away.

Clif
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