Hello everybody, it's ever interesting to read that somebody else has some troubles as experienced from myself ;-) Me too am grateful to Andy for the support I received while struggling with odd expe
Hi Marco, I don't detect any heat in the LPF but at this low power level it could be difficult to detect it. I already have plans to build the big T type LPF. I have the T-225A-2 cores and metal to m
Hi Paul, Out of curiosity I've done some spice simulations of your PA. They indicate that a T type LPF won't help at all. This was to be expected because your PA is not a class D voltage mode push pu
Hi Clemens, Thank you for taking the time to run these simulations! My Ultimate 3S does have a LPF before the feed to the PA. I understand some PAs prefer a square wave. Should I remove the LPF? I ha
I was able to make a few more tests without getting frostbite. :) I disconnected the coax from the matching transformer (at the antenna) and put the coax into a dummy load. All OK, exactly the same a
Hi Paul, No! It helps reducing harmonics output of the PA which in case are reflected by the LPF to the FET and MAY cause instability and IMD. That's why *sometimes* diplexer filters are used. They s
Hi Paul, Am 28.12.2017 21:57, schrieb N1BUG: It seems the problem must be RF getting into something, RF current where it does not belong, but only when feeding the antenna. An important note: There i
During the night I made a few more tests... Iso xfmr at PA output. 14T:14T on FT-114-JC core. Made the problem slightly WORSE. Iso xfmr at amp input. 4T:4T on 3 x BN73-202. Made the problem slightly
One final thing. Thought maybe something in the antenna was breaking down (arcing or corona), so made another check: I now have the capability to run the PA on 13V or 19V. At 19V I can make more powe
Hello N1BUG, What does the scope show if you look at each side of the choke in the PA? I did some tests ages ago using the stacked chip caps on the PA side of the choke compared to conventional leade
Hi Chris, At PS side of the choke, no RF behaving or misbehaving. At output transformer side of the choke, mainly negative-going pulses which become distorted similarly to the output when misbehaving
Sounds more like feedback. RF feeding back into the driver stages. The LF component you see is, perhaps, a beat between generated RF and oscillatory RF due to feedback. Or feedback itself oscill
Hi Paul, Basically yes. But we don't know how much capacitively coupling there is between primary and secondary which might partially spoil the RF isolation. I would just give it a try: One chocke at
Hi Clemens, OK, I understand about capacitive coupling in transformers. So I tried a simple common mode choke. At first 22 turns using RG-178 coax on a FT-114-JC (yes, made a typo last time). No chan
Hi Markus, Could the scope "blurring " be caused by a high-frequency rather than low-frequency oscillation? It's possible but what I see is not what I would expect in that case. My experience has usu
Thanks Andy. Assuming by driver stages you mean what is external to the PA, the exciter. This is one reason I tried driving it with the function generator (HP 3325B) instead of the usual exciter (QRP
Hi Paul, 22 turns on one FT114-J core is more than adequate. It gives you an XL of - j1.291k which in turn means an attenuation of around 22dB (referenced to 50 Ohms) for common mode currents. So shi
