locked Re: Yaesu FT991A Won't Transmit in FT8 #NewUser #Cat_RigControl #transmit #Yaesu #TechnicalHelpQuestion

Reino Talarmo

Hi Ropert,

The sensitive part of your installation is the connection between your radio and MacBook. I think you mentioned it to be a USB cable. A quite low common mode current on the cable do enter into your rig and MacBook sensitive digital circuits disturbing USB communication. How the RF current enters through USB connections depends on how the circuitry and cable screens are wired. Further information is e.g. in Jim's papers: k9yc.com/RFI-Ham.pdf presents the concepts; k9yc.com/2018Cookbook.pdf presents designs of effective transmitting chokes for the HF bands. Note that a common mode choke works correctly, when there is a low RF impedance to ground on the both side of the choke. A short wire to "real" ground would be best.

SSB does not normally use at all the rig - MacBook communication unless you have some logging program in use. You could get RF burns, if you rig and microphone happens to be in high impedance point of your "antenna system". In any case radio - computer interfaces can be much more sensitive than human can sense, or should I say "is".

It could be possible that something is damaged in the radio as well due to high RF current/voltage 100 W transmission can generate. Does SSB or CW still works or have you lost all transmission capability?

The antenna manufacturer does not tell the whole story how an end fed antenna actually works by the laws of physics (any current needs a return bath). By the way in the recommendations of the European radio amateur training discourages use of EFHW antennas due to the fact that the user needs to deal with the "missing half of the antenna". Please note that know how well EFHW can work, when a suitable "grounding" arrangements are used and power level is not too high, say 10 W. In most cases the antenna feed point in those cases is close to ground, not elevated as in the installation instructions you referred.

You could try a counterpoise from the outer cell of the antenna connector and a current balun on the feedline. Even better could be to insert the current balun where the feedline goes close to ground and connect the feedline outer conductor to ground at that point. Unfortunately that may affect to the SWR values. I could not deduct how they simulated radiation patterns in Figure 4. Well at least they had a perfect ground.

73, Reino OH3mA

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