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Gordon Gibby
¿ªÔÆÌåÓý?Do you know why they didn't use 49*50 ohms as their termination?? ?
I didn't read the email trail (sorry, just not enough time in this world) but it seems like you could make a dummmy load for that if necessary.? ?
What I have gleaned out of all this argumentation back-and-forth is that these things can have single-digit losses if working into a resonant piece of wire.? ?And that using a tuner is preferable. [I always work for lowest losses personally.]? Some of our
newer hams locally are very limited in their "radio assets".? ?We'll be building uBitx's beginning in a bout 3 weeks.? We have already built 11 knockoffs of the Buckmaster off-center fed antenna and I hope to high heaven we built baluns etc with single-digit
losses!!? ?At any rate, it will be a huge improvement over what most of them had beforehand (NOTHING HF).? ? Their skills are growing and I've learned a lot from all the discussions of various "issues" on this forum.? ?
After we get the "stock units" working, hopefully with v4 factory software and setting the oscillator numbers precisely in the code itself, we will begin on some of the most important improvements, which I haven't had time to get to quite yet....one year
ago these hams?didn't know a resistor from a transistor.....
cheers,
gordon
From: [email protected] <[email protected]> on behalf of Warren Allgyer <allgyer@...>
Sent: Wednesday, August 1, 2018 8:53 AM To: [email protected] Subject: Re: [BITX20] End Fed antennas w/ uBITX ?
I have been asked by private message what it is about the QST Review test methodology that I found invalid. I constructed this explanation of their test in response and I would like to share it with the group. When testing a 49:1 transformer however, there is no way to adjust the termination to 50 ohms. So, with an 800 ohm load selected in the load box as the authors specify in the email trail, the RF Source and the source power meter are operating in a 16 ohm environment. What the actual power out of the source is, and what power is indicated on the source power meter with a 16 ohm load, are determined by the characteristics of each box. It most certainly cannot be assumed to be 10 watts. The error in this step can easily be over 6 dB. When the test therefore shows the transformer to have a loss of 0.2 dB, the actual loss could be as much as 6.2 dB. The two transformer back to back test that I have documented does not suffer from a load mis-match and is therefore a far more appropriate way to do this measurement. |
