1.? This thread has been running since Oct 6, now 15 days.? ?Many, many sets of data have been presented, including photos of the measurement setup.? ?There were initial unforced errors due to a DIODE in the Heathkit Cantenna system that added its own spurious responses.? ? The setup has been validated by (a) measurement of an Icom 718 commercial transceiver and (b) measurement of an externally filtered SN#141 sBitx V2 that demonstrated CLEAN output.
2.? ?Despite running for over 2 weeks, not a single other serial number of a production unit has been documented.? ?Perhaps I'm wrong, but I believe the ONLY production unit delivered to a customer whose output has been checked for compliance with spurious response regulations in the United States, is unit #141 -- and it is failing on some bands.? ?
3.? ?A licensed radio amateurs we are compelled to operate kits and other homebrew equipment (after some date) that comply with the spectral purity requirements.? ?The ARRL takes this very seriously and has initiated a Clean Signals Initiative
Web Page:? ?
QST article:? ?
to advance the purity of amateur transitters, specifically noting the problem with LDMOS and MOSFET amplifiers.? ??
4.? The sBitxV2 low pass filters look great in my estimation, yet the signals that I'm recording afterwards don't always bear that same excellence.? ? No one has published any spectrum of a customer-received unit otherwise.? ??
5.? I've now shown that at least ONE diode in the post-filter system appears to be generating (on one band) spurious responses (harmonics) that are above spec.? ??
6.? It appears to me that the next logical step is to isolate the amplifier output, and connect it DIRECTLY to one of the low pass filters,and then DIRECTLY to a dummy load and attenuator system for monitoring with a spectrum analyzer so that all of the associated diode switching, control circuitry, DC voltage generation circuitry, and SWR measurement can be put aside temporarily.? ? I would EXPECT that the result will generally be a "clean signal".? ?The resulting test schematic might look like this:
7.? ?If we can't fix this -- or demonstrate that these measurements have had an ERROR, or that the unit is damaged or not representative of the vast majority of manufactured units -- then I doubt we will ever get the ARRL to publish a complimentary review and this is such a fine effort that it deserves to get acclimation and approval from the ARRL.? ?Ashhar has put a HUGE amount of work into this, and deserves to get credit for his work.? ?The rest of us can pitch in to prove the outcome one way or the other.? ? ?I'm now out of town for a week and hope to get back and eventually take the next step.? ? I've learned a LOT in this process and corrected some of my measurement errors.? ?Perhaps there are others to correct?? ?Haven't seen any contradictory examples however, and able to clearly show CLEAN transmissions in at least two other instances.... so I think this needs further investigation and correction.
73
Gordon KX4Z
