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PostPosted: Sat Nov 28, 2015 3:08 am 
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Joined: Sat Nov 28, 2015 2:40 am
Posts: 3
Hello,

Following comments about distorted signal during QSOs despite sending into the antenna feed significantly less than 50 watts (according o the PEP show on the display), I set up an experiment to measure the compression point of my amplifier. The setup is simple: The amplifier is driven by a trx generating CW signal, the output is connected to a dummy load, and the input and output signal measured using oscilloscope. To my surprise the numbers show by the amplifier did not much power calculated using measured RMS voltage of the signal. Quick analysis of the numbers showed that the measure and indicated power differ by a factor of 0.785 (see the plot below).

The transformers are wound according to the manual, so for CW signal the PEP power should be equal. Is there a way to calibrate the power meter? If not, would it be possible to add in future FW releases a hidden service menu where the scaling coefficients could be set (supply voltage and heatsink temperature are also slightly off).

Regards,
Jacek, KW4EP.

EDIT: Adding attachments doesn't seem to be working. I can email the graph.
EDIT2: Link to the graph on dropbox: https://www.dropbox.com/s/f3bzs45pwmqag ... inrpwr.png


Attachments:
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hr50_pwr_vs_inrpwr.png
hr50_pwr_vs_inrpwr.png [ 34.57 KiB | Viewed 4489 times ]


Last edited by KW4EP on Sat Nov 28, 2015 1:05 pm, edited 1 time in total.
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PostPosted: Sat Nov 28, 2015 8:42 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
Hi Jacek,

Yes, please email me the plots, I'd love to see them; jim (at) hobbyPCB (dot) com. The latest firmware (V3.0D) does have a meter calibration in the menu. I haven't found an amp that couldn't be calibrated even when T3 has 11 turns. The 1N4148 diodes used to derive the power signals seem to have a large unit-to-unit variation. I generally set the power to 20M, 50W on my Bird 43 then adjust the HR50's meter to do the same. After that it's within 10% (0.5 dB) at 50W output 160-6M.

73,
Jim WA2EUJ


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PostPosted: Sat Nov 28, 2015 2:52 pm 
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Joined: Sat Nov 28, 2015 2:40 am
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I adjusted the correction, but it's still not enough. I'll have to check again the transformer.


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PostPosted: Sun Nov 29, 2015 4:08 pm 
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Joined: Thu Jan 09, 2014 11:10 am
Posts: 68
KW4EP wrote:
Following comments about distorted signal during QSOs despite sending into the antenna feed significantly less than 50 watts (according o the PEP show on the display), I set up an experiment to measure the compression point of my amplifier. The setup is simple: The amplifier is driven by a trx generating CW signal, the output is connected to a dummy load, and the input and output signal measured using oscilloscope. To my surprise the numbers show by the amplifier did not much power calculated using measured RMS voltage of the signal. Quick analysis of the numbers showed that the measure and indicated power differ by a factor of 0.785 (see the plot below).


The power meter on my HR50 is 'pretty close' and serves my needs well enough.

But I too found some room for a tweak or two. For example, take a look here:

http://forums.qrz.com/index.php?threads ... 52.433522/

and you'll see why other radios use a different diode (my pick is the 1N5711) for the purpose.

To be fair, these diodes are rather sensitive compared to the '4148 and can fry easily from ESD and pulse events.
Also, they cost 44 cents each versus 10 cents for a '4148, in onesies.

I'd actually like a firmware option to choose one type diode over another.


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PostPosted: Sun Nov 29, 2015 8:57 pm 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
The firmware has about 200 bytes of free memory. We're looking at converting the wattmeter and SWR calculations from floating point to a clever fixed point scheme to see if we can free up some room for new features. I'd like to get digital support for the FT-817 and the Elad FDM as well.

Jim WA2EUJ


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