[hpsdr] munin power

[FRANCIS CARCIA]

Hi All,
I have been spending weeks carefully building and testing broad band transmission line transformers to gain more understanding of what it takes to build an efficient transformer. My best so far is a 1:2 TLT 160 through 6 meters .15dB worse case on 10m.  I've checked a number of published designs and find losses close to 1dB.
The first thing I learned was that small coax like RG188 and RG316 loses about .25dB/foot at 50MHz.
This is at 0dBM. When you try to push a couple hundred watts through the stuff the loss increases. I got RG188 so hot it melted plastic spacers supporting the cores at 300w PEP. 
The center conductor is only #26 stranded wire. As it heats up the resistance increases. I first noticed this on my 300 watt MRI amplifier. So you might check your coax connections. RG58 also gets pretty lossy as frequency is increased. I replaced my test cables with RG400 to reduce this loss so I measured the actual output power not attenuated by cable loss.  My Bird 43 hangs off the dummy load connector. If you are worried about your load reactance put up a 10 meter and 6 meter dipole as a load.
The output transformer on Munin must be installed with very short connections or leakage inductance will
hurt high frequency performance. I bought two Munin amps but have not built them. When I get a little smarter I may build both transformers and mount them on my fixture joined at the low Z ports and check them. It will be a while before I get to the 1:16 TLT.
Frank WA1GFZ
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