TX and Watt meter calibration

[JJ4SDR]

Did TX calibration (PA settings some time ago) and also Watt meter calibration using a 50 ohm dummy load and a BIRD 43 Thruline RF power meter.

I read in the PowerSDR sub-forum about this topic as well and non-linearity between what "Drive" says and the actual RF power out from PowerSDR (Thetis?). Certainly, I don't want to overdrive my amp and noticed something definitely had changed after PA settings were modified based on RF power out readings provided by the BIRD. Easily getting 600 W out on 40 but only 400-500W on 20 now. Have yet to check what kind of readings I am getting now, after the Watt meter calibration. Perhaps I adjust the "Drive" for each band of operation (going by the calibrated RF power out readings provided by Thetis) when I am using the amp so that I am not over-driving the amp. I assume that "Drive" settings for each band are also saved in any Database Export so I should be good provided nothing else changes in the station (such as a new amp, antenna etc.)?

Below, see screen-shots of calibration results and also BPF1/BPF2 data. I have not modified or touched any of the BPF data/settings.



JJ

[JJ4SDR]

Did TX calibration (PA settings some time ago) and also Watt meter calibration using a 50 ohm dummy load and a BIRD 43 Thruline RF power meter.

I read in the PowerSDR sub-forum about this topic as well and non-linearity between what "Drive" says and the actual RF power out from PowerSDR (Thetis?). Certainly, I don't want to overdrive my amp and noticed something definitely had changed after PA settings were modified based on RF power out readings provided by the BIRD. Easily getting 600 W out on 40 but only 400-500W on 20 now. Have yet to check what kind of readings I am getting now, after the Watt meter calibration. Perhaps I adjust the "Drive" for each band of operation (going by the calibrated RF power out readings provided by Thetis) when I am using the amp so that I am not over-driving the amp. I assume that "Drive" settings for each band are also saved in any Database Export so I should be good provided nothing else changes in the station (such as a new amp, antenna etc.)?

Below, see screen-shots of calibration results and also BPF1/BPF2 data. I have not modified or touched any of the BPF data/settings.



JJ

Forgot to included these data ("Drive" set to 50 on each band). I don't do 60 meter so I didn't bother calibrating there.

Band/RF Power Out
160m/65W
80m/78W
40m/91W
30m/92W
20m/95W
17/93W
15m/90W
12/70W
10/80W
6/37W

I used to get 600W out from the Amp when using an analog transceiver, exciting the Amp with approximately 50 W.

[NC3Z]

A couple of schools of though discussed here before.

Calibrate your PA for 100W out when the slider is at 100, then use DDUtil to tailor your output per band via CAT control of the Power sliders.

Or calibrate your 100% slider to give you your desired output of your amplifier for each band. This way you will never need to worry about overdriving your amp. This is how I have my 7000DLE setup.

[w-u-2-o]

First of all, know that the frequency settings for the hardware filters only determine when each filter is selected. They don't actually change the filter edges or shapes. The designs are third order BPFs, so preselection is pretty gradual. I run with all of mine bypassed.

Second, when it comes to PA calibration, because the fairly bad non-linearity of the drive control makes it so that accurate results are only achieved near one drive setting as opposed to all drive settings, all you can do is choose from one of the following two calibration approaches:

1. Calibrate so that a drive setting of 100 results in 100W. Then make notes on what actual drive settings are for actual power levels below 100W.

2. Calibrate so that the drive setting is accurate at the power level you normally use to drive your amp. For example, if you want 50W drive, set the drive to 50, calibrate for 50W, and that way you know when you set it to 50 you get what you want. Again, for other values of drive, you'll have to keep notes, or look at the power meter reading.

Calibrations, and non-linearities, will be different for every band.

It's worth noting that essentially all of the non-linearity is in the pre-amp and amp sections, and this is what has the effect of knocking the drive control out of whack. Output of the DAC is pretty darn linear.

[JJ4SDR]

A couple of schools of though discussed here before.

Calibrate your PA for 100W out when the slider is at 100, then use DDUtil to tailor your output per band via CAT control of the Power sliders.

Or calibrate your 100% slider to give you your desired output of your amplifier for each band. This way you will never need to worry about overdriving your amp. This is how I have my 7000DLE setup.

Hi Gary,

Appreciate the advice. I am inclined to go with the 2nd choice you are suggesting.

Best!
JJ

[JJ4SDR]

First of all, know that the frequency settings for the hardware filters only determine when each filter is selected. They don't actually change the filter edges or shapes. The designs are third order BPFs, so preselection is pretty gradual. I run with all of mine bypassed.

Second, when it comes to PA calibration, because the fairly bad non-linearity of the drive control makes it so that accurate results are only achieved near one drive setting as opposed to all drive settings, all you can do is choose from one of the following two calibration approaches:

1. Calibrate so that a drive setting of 100 results in 100W. Then make notes on what actual drive settings are for actual power levels below 100W.

2. Calibrate so that the drive setting is accurate at the power level you normally use to drive your amp. For example, if you want 50W drive, set the drive to 50, calibrate for 50W, and that way you know when you set it to 50 you get what you want. Again, for other values of drive, you'll have to keep notes, or look at the power meter reading.

Scott: #2 is what I opine will do for me. Thanks! JJ

Calibrations, and non-linearities, will be different for every band.

It's worth noting that essentially all of the non-linearity is in the pre-amp and amp sections, and this is what has the effect of knocking the drive control out of whack. Output of the DAC is pretty darn linear.

Roger on that!

[JJ4SDR]

Played with the amp on 20 just now. After today's TX and Watt meter of Thetis calibration it seems that I am not getting 600 W out from the amp even when the Watt meter inside Thetis shows approximately 70 watts on peaks! That is a level that I don't want to see from any exciter. For a look see, I pushed the "Drive" to about 60 with only a marginal increase from the amp. That being "marginal" I am not going to bother (as nobody will hear the difference any way) and would rather stick with a drive power of approximately 50 W as I have been doing for many years. Not sure if the CFC settings may factor into the RF out from amp? Even if they did, wouldn't I be able to see the amp put out 600 W on peaks? I am using a peak-reading (w/hold) watt meter to observe RF out on peaks. Truth be told, the CFC settings are very different from what I had in line when I used my analog transceiver (and VST plug-ins) so this comparison isn't necessarily an "A2B." This might have something to do with what I am observing.

Tried the above test with my other 20 m antenna as well (I do have an external Palstar, manual ATU in line, but I don't really need on this antenna I wanted to test on), but got fairly similar results.

JJ

[w-u-2-o]

You should be able to drive your amp to its rated max. power with TUN or two-tone. Can you not do that?

Are you running PureSignal? Are you running it with an external coupler for the amp?

[JJ4SDR]

Tried both (two-tone worked better) but it seems that I would drive the Grid current on the amp (AL-811H) way too high for the power out that I was used to seeing when using my old transceiver.

This sounds like an amp problem or an amp operator problem and not a radio problem.

P.S. you need to learn to use the quote function properly if you are going to use it. You need to preview your posts to make sure they format correctly. It is very hard to read your posts otherwise. You might not want to use the quote function if you don't understand how it works.