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I’ve successfully assembled a qdx, wrapped for 12v power supply.
When I power it off a “car battery “ power output shows around 15 watts on 20 &40
Swr is 1.1 -1
If I use a 12, 500ma wall wort power shows 2-3 watts.
If I use a 12 volt1.5 amp wall wort power shows 15 -30 watts.
I’ve been running it on the 500ma at around 3 watt. But I’m at a loss as to why / how this wide of a change can be happening.
I tried powering it with 9v wall wort just to make sure I didn’t miss the toriod wrap count.
Any thoughts on what to look at?
Matt
Kj7lud
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I think you must be short of some decimal places somewhere ???? ?
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On 01/02/2024 16:08, Bruce Akhurst wrote: I think you must be short of some decimal places somewhere ??? Or some useless power meters. Alan
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It's a Dosy CB power meter ... the best money-maker that CB techs ever had.
Remember that if your power meter isn't calibrated, but is linear relative to the displayed power, it's still a useful tool.? It just isn't useful for exactlywatt?readings.? For that, you need something that IS calibrated, or at least can be calibrated.
73 Jim N6OTQ
On Thu, Feb 1, 2024 at 10:24?AM Alan G4ZFQ < alan4alan@...> wrote: On 01/02/2024 16:08, Bruce Akhurst wrote:
> I think you must be short of some decimal places somewhere ???
Or some useless power meters.
Alan
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The meter I’m using is mighty fine junk, (mfj)? Manual tuner with meter. I’m not using the tuner as the end fed sloper I’m using is giving a good match.? I’ll grab some picture of it with the various power supplies.? What is everyone else using to power a 12volt qdx? Or what’s the recommended way to power it??
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On Feb 1, 2024, at 9:53?AM, Jim Strohm <jim.strohm@...> wrote:
? It's a Dosy CB power meter ... the best money-maker that CB techs ever had.
Remember that if your power meter isn't calibrated, but is linear relative to the displayed power, it's still a useful tool.? It just isn't useful for exactlywatt?readings.? For that, you need something that IS calibrated, or at least can be calibrated.
73 Jim N6OTQ On Thu, Feb 1, 2024 at 10:24?AM Alan G4ZFQ < alan4alan@...> wrote: On 01/02/2024 16:08, Bruce Akhurst wrote:
> I think you must be short of some decimal places somewhere ???
Or some useless power meters.
Alan
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12V or less. No more than 12V. A 13.4V supply is asking for trouble.?
I have a rev 2 qdx wired for 9V and I get 3.5-4W on all bands. Powered with a Chinese “LED Supply” power supply turned back to 9.0V.?
Larry KB3CUF?
The meter I’m using is mighty fine junk, (mfj)? Manual tuner with meter. I’m not using the tuner as the end fed sloper I’m using is giving a good match.? I’ll grab some picture of it with the various power supplies.? What is everyone else using to power a 12volt qdx? Or what’s the recommended way to power it?? Thanks? ? It's a Dosy CB power meter ... the best money-maker that CB techs ever had.
Remember that if your power meter isn't calibrated, but is linear relative to the displayed power, it's still a useful tool.? It just isn't useful for exactlywatt?readings.? For that, you need something that IS calibrated, or at least can be calibrated.
73 Jim N6OTQ On Thu, Feb 1, 2024 at 10:24?AM Alan G4ZFQ < alan4alan@...> wrote: On 01/02/2024 16:08, Bruce Akhurst wrote:
> I think you must be short of some decimal places somewhere ???
Or some useless power meters.
Alan
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Did you buy that MFJ meter new?? If not, then somebody may have opened it up and got to it with the old golden screwdriver. ? IIRC, most of that kind of meter have a variable resistor for adjusting the meter into something approaching calibration -- or turning it to show maximum power.
The ?cheapest CB power meters had a fixed resistor that?was selected by testing the meter in the factory.
It's not that these adjustable power meters are bad.? In fact, some of them are very nice for QRP use, and can be tweaked to reasonable accuracy as long as you have a calibrated power meter that covers the same range as the cheapo, and a reliable power?source -- like a 27 MHz CB. ?
Among the reasons that 73 magazine printed nearly 80 articles for converting CB radios for the ham bands was that they were?cheap and reliable rigs.? Eventually I'll gather up all my old CBs and test them, so I can fix or convert them for 10M.
And if they have a built-in power meter, I'll adjust it so when it says 5 watts, that's what the radio is actually putting out.
73 Jim N6OTQ ?
The meter I’m using is mighty fine junk, (mfj)? Manual tuner with meter. I’m not using the tuner as the end fed sloper I’m using is giving a good match.? I’ll grab some picture of it with the various power supplies.? What is everyone else using to power a 12volt qdx? Or what’s the recommended way to power it?? Thanks? ? It's a Dosy CB power meter ... the best money-maker that CB techs ever had.
Remember that if your power meter isn't calibrated, but is linear relative to the displayed power, it's still a useful tool.? It just isn't useful for exactlywatt?readings.? For that, you need something that IS calibrated, or at least can be calibrated.
73 Jim N6OTQ On Thu, Feb 1, 2024 at 10:24?AM Alan G4ZFQ < alan4alan@...> wrote: On 01/02/2024 16:08, Bruce Akhurst wrote:
> I think you must be short of some decimal places somewhere ???
Or some useless power meters.
Alan
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I did buy it new, also when I put my 991a on it and set power down it seems to be fairly accurate with what power I’m putting into it.? Granted it’s not certified but just one step I was trying in trouble shooting.?
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On Feb 1, 2024, at 10:16?AM, Jim Strohm <jim.strohm@...> wrote:
? Did you buy that MFJ meter new?? If not, then somebody may have opened it up and got to it with the old golden screwdriver. ? IIRC, most of that kind of meter have a variable resistor for adjusting the meter into something approaching calibration -- or turning it to show maximum power.
The ?cheapest CB power meters had a fixed resistor that?was selected by testing the meter in the factory.
It's not that these adjustable power meters are bad.? In fact, some of them are very nice for QRP use, and can be tweaked to reasonable accuracy as long as you have a calibrated power meter that covers the same range as the cheapo, and a reliable power?source -- like a 27 MHz CB. ?
Among the reasons that 73 magazine printed nearly 80 articles for converting CB radios for the ham bands was that they were?cheap and reliable rigs.? Eventually I'll gather up all my old CBs and test them, so I can fix or convert them for 10M.
And if they have a built-in power meter, I'll adjust it so when it says 5 watts, that's what the radio is actually putting out.
73 Jim N6OTQ ? The meter I’m using is mighty fine junk, (mfj)? Manual tuner with meter. I’m not using the tuner as the end fed sloper I’m using is giving a good match.? I’ll grab some picture of it with the various power supplies.? What is everyone else using to power a 12volt qdx? Or what’s the recommended way to power it?? Thanks? ? It's a Dosy CB power meter ... the best money-maker that CB techs ever had.
Remember that if your power meter isn't calibrated, but is linear relative to the displayed power, it's still a useful tool.? It just isn't useful for exactlywatt?readings.? For that, you need something that IS calibrated, or at least can be calibrated.
73 Jim N6OTQ On Thu, Feb 1, 2024 at 10:24?AM Alan G4ZFQ < alan4alan@...> wrote: On 01/02/2024 16:08, Bruce Akhurst wrote:
> I think you must be short of some decimal places somewhere ???
Or some useless power meters.
Alan
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On Feb 1, 2024, at 10:21?AM, Idaho Fluke via groups.io <mattfidaho@...> wrote:
? I did buy it new, also when I put my 991a on it and set power down it seems to be fairly accurate with what power I’m putting into it.? Granted it’s not certified but just one step I was trying in trouble shooting.? On Feb 1, 2024, at 10:16?AM, Jim Strohm <jim.strohm@...> wrote:
? Did you buy that MFJ meter new?? If not, then somebody may have opened it up and got to it with the old golden screwdriver. ? IIRC, most of that kind of meter have a variable resistor for adjusting the meter into something approaching calibration -- or turning it to show maximum power.
The ?cheapest CB power meters had a fixed resistor that?was selected by testing the meter in the factory.
It's not that these adjustable power meters are bad.? In fact, some of them are very nice for QRP use, and can be tweaked to reasonable accuracy as long as you have a calibrated power meter that covers the same range as the cheapo, and a reliable power?source -- like a 27 MHz CB. ?
Among the reasons that 73 magazine printed nearly 80 articles for converting CB radios for the ham bands was that they were?cheap and reliable rigs.? Eventually I'll gather up all my old CBs and test them, so I can fix or convert them for 10M.
And if they have a built-in power meter, I'll adjust it so when it says 5 watts, that's what the radio is actually putting out.
73 Jim N6OTQ ? The meter I’m using is mighty fine junk, (mfj)? Manual tuner with meter. I’m not using the tuner as the end fed sloper I’m using is giving a good match.? I’ll grab some picture of it with the various power supplies.? What is everyone else using to power a 12volt qdx? Or what’s the recommended way to power it?? Thanks? ? It's a Dosy CB power meter ... the best money-maker that CB techs ever had.
Remember that if your power meter isn't calibrated, but is linear relative to the displayed power, it's still a useful tool.? It just isn't useful for exactlywatt?readings.? For that, you need something that IS calibrated, or at least can be calibrated.
73 Jim N6OTQ On Thu, Feb 1, 2024 at 10:24?AM Alan G4ZFQ < alan4alan@...> wrote: On 01/02/2024 16:08, Bruce Akhurst wrote:
> I think you must be short of some decimal places somewhere ???
Or some useless power meters.
Alan
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First of all, get yourself a good digital voltmeter/multimeter. As a serious kit builder, you will use it a lot.
Most of the wall AC/DC power adapters are notoriously mislabeled. If you want to use one for your project, measure its voltage under no load and full load. Make sure it is not higher than 12 Volt. Many of them do not have a good voltage regulator built in. Don't use the QDX as the test load. I use a combination of power resistors. Under full load, also measure the AC component. It should be less than about 50 millivolts.
About power measurement: Most commercially available (low-cost) power meters are not accurate enough to be used to optimize the output power of a multiband QRP transmitter. If the power meter is built for measuring high power as well, then they may be 50% or more off on QRP power levels. They are not calibrated for all the bands we are interested in. Over the years, I found a simple method to measure RF power with reasonable accuracy and low cost. I use the dummy load of QRP-Labs with its peak voltage sensor output. Under load, I measure the DC voltage of this sensor output. I add 0.5 Volt for the diode loss then I multiply the result by itself (square it). I divide the result by 100, and you will get the accurate value of the power injected into the dummy load in Watts. It works equally well for all shortwave bands.?
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Ok, ?thanks for the help.
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On Feb 2, 2024, at 10:34?AM, aa0jr Jakob via groups.io <aa0jr@...> wrote:
?First of all, get yourself a good digital voltmeter/multimeter. As a serious kit builder, you will use it a lot.
Most of the wall AC/DC power adapters are notoriously mislabeled. If you want to use one for your project, measure its voltage under no load and full load. Make sure it is not higher than 12 Volt. Many of them do not have a good voltage regulator built in. Don't use the QDX as the test load. I use a combination of power resistors. Under full load, also measure the AC component. It should be less than about 50 millivolts.
About power measurement: Most commercially available (low-cost) power meters are not accurate enough to be used to optimize the output power of a multiband QRP transmitter. If the power meter is built for measuring high power as well, then they may be 50% or more off on QRP power levels. They are not calibrated for all the bands we are interested in. Over the years, I found a simple method to measure RF power with reasonable accuracy and low cost. I use the dummy load of QRP-Labs with its peak voltage sensor output. Under load, I measure the DC voltage of this sensor output. I add 0.5 Volt for the diode loss then I multiply the result by itself (square it). I divide the result by 100, and you will get the accurate value of the power injected into the dummy load in Watts. It works equally well for all shortwave bands.?
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Bruce Akhurst