Re: Harmonics measured by Warren. How bad?

Bill Cromwell

Hi Brent,

First,I cannot comment on whatever an l-match is unless you an l-network to match the transmitter for 50 ohms. The usual configuration has the inductor in series and the tuning cap to ground at the output end. That configuration is low pass and is just what the doctor ordered. One of the other configurations is high pass and will not help.

Low pass type antenna tuners have been cited as reducing the harmonics to legal levels in the U.S. I am using such tuners here while I am also building low pass and maybe band pass filters to go in-line between the transmitter and everything else downstream.

If we twist all knobs full right and change resistors to try and get a couple more watts (of overdrive?) then nasty byproducts get much worse. HF Signals says the microbitx is a ten watt radio on 80 meters and the power out drops as we go up in frequency. That is how I treat mine.

As for the olde daze, the required specs were a lot more lax than now. I'm sure you must have heard about all the RFI and TVI caused by hams using those old rigs (even though they were new at the time). Your comments are comparing apples to bananas. To quote one of my grandfathers, "the only thing good about the good old days is they are gone".

Those undesired products are removed with some types of tuners. I think Allison delineated some of them including L-networks. She has provided a lot useful info here. Others are working on internal mods to improve the uBitx performance and I will probably add something to mine. Later. Anything worthwhile along that line is going to be major surgery. The box I made for mine may not have enough space for any daughter boards. Hint, hint.

Let me recommend the CEC software for your uBitx after you get it working. Search terms include "KD8CEC", the author of the software. I am not using all the features available with his software but it makes the uBitx much more user friendly and makes CW really usable. I made a simple mod to control the CW sidetone level. Without that your ears will bleed. I am living without AGC or S-meter. They are not needed by me but you may want them for yourself. Louder is S-more and weaker is S-less:)

If you add all the mods with available kits and include the larger, touch screen displays the overall cost is much less attractive. That does not matter to some of the uBitx owners. Some of bought to experiment and lean. Enjoy *your* radio.


Bill KU8H

On 08/26/2018 12:55 PM, Brent Seres wrote:
Hmmm...built and modified the Bitx40, now awaiting the ubitx. I didn't
see this thread before ordering, but it will be an interesting learning
experience. I shall have to see what the harmonics and spurs look like
on my unit. Has anyone done any tests on what an l-match ATU does, if
anything, to reduce the spurs and at the entire
system, not just the board itself? Personally, I'm fine with adding
external lpf on the antenna as well. I shall also see what my 40 - 15
mag loop does with its extremely sharp tuning. Modern tequniques (wide
band amps) are great, but maybe there is something to be said for the
old 'dip and load' of my dx20 and dx60 that I used in the stone age.
Thanks to all for posing test results. Makes you wonder how we survived
in an Era when many of us only had a VOM for test equipment. When I
think of some of the things I did as a new ham at age 15, the term
'smoke and flash' takes on a whole new meaning....

Again, thanks for the info
bark less - wag more

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