T/R switch and SWR bridge notes

[Nick Kennedy]

I got the T/R switch and SWR bridge built.  Whew, I can't believe I got that MSOP IC soldered in and I hope I never have to solder in another 0603 part in this lifetime!

Mouser didn't have the SMT 1N5711 diodes and I wound up installing leaded parts. I stacked and glued together two FT50-61 cores for each toroid.

Thus far I've checked forward power and SWR readings with a 50 ohm load only, using my K3 to supply RF power. SWR readings are typically about 1.09, which I think is good for this circuit.

The published formula for power gives me readings that look about 20% high. From my notes:

·        The calculated powers are all about 20% high. I suspect the posted formula of Pfwd = 2 * (1.57 * Vf + 0.05)^2 is not right. At the maximum measurement of 5.0 VDC, it predicts 120 W.

·        I did a check of my K3 power settings versus my Arduino power meter on 40 meters, 5 watts to 100 watts and they agree fairly closely. So I’m going to say my K3 power settings are true power, as best as I can determine.

·        I empirically played with the factors of 1.57 and 0.05 in the formula and came up with my version which is P = 2 * (1.394 * Vf – 0.1)^2. This gives me agreement within -5.2% to +2.0% as I measure 5, 10, 25, 50, 75 & 100 watts.

I'm pleased to have gotten this far. I have my 100 W amplifier working. Now I need to integrate it all together. I want to write an Arduino program to crunch the numbers and provide readout and protective actions.

73

Nick, WA5BDU

[Ulf (SM0NOR)]

Hi Nick,

I'm reading your post with interest! Have you made any measurements on the other bands? If so, it would be interesting to compare measurements. On my side I don't have a calibrated watt meter. I'm measuring with the built-in meter in a Palstar DL2K dummy load. This is not ideal as the scale goes up to 500W, so my reading could be off with 10% or worse. Still, the measurements aligns fairly well with the calculated value. However I find the 20 meter result a bit strange since I'm reading 3.3A at 50V. This implies an efficiency of 76% , which I find hard to believe. At the moment I'm doing cabinet work so the boards are disassembled, but it will be up and running again in a week or so. I attach my measurements.

[jcve...@gmail.com]

Here are the measurements I made on the original coupler:

Band (M)        Drive (W)        Output (W)        Input SWR        Vf 100W        Vf 50W        Vf 20W         VF 10W
160                1.2                      100                   1.0                      4.95               3.67              2.34            1.74
80                  1.1                      100                   1.1                      4.70               3.41              2.15            1.60
60                  1.0                      100                   1.2                      4.64               3.34              2.12            1.57
40                  0.9                      100                   1.2                      4.56               3.31              2.08            1.54
30                  1.1                      100                   1.4                      4.52               3.29              2.08            1.53
20                  2.0                      100                   1.3                      4.51               3.27              2.07            1.53
17                 1.0                       100                   1.2                      4.51               3.28              2.07            1.53
15                 1.2                       100                   1.3                      4.53               3.30              2.08            1.54
12                 1.2                       100                   1.1                      4.53               3.28              2.08            1.54
10                 1.4                       100                   1.1                      4.53               3.30              2.08            1.53
6                   2.0                       100                   1.3                      4.84               3.50              2.21            1.61