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Re: CQWW VHF
¿ªÔÆÌåÓýHi Zack, ? I believe that the circuit is actually protected against shorts as Q3013 and R3045 work as a current limit to prevent it putting too much current into the antenna. ? I think that Q3008 and Q3009 are used to select the actual voltage to put on the ANT line so one puts about 12V onto the line and the other puts a reduced voltage of around 8V onto it. My guess is that the ANCV line controls the voltage and the ANNG is feedback as to what voltage is being fed to the antenna. ? Also, if you have the antenna selection on anything except ATAS in the menu, then I think the above circuit would be inhibited as it doesn¡¯t require any voltage on the antenna cable unless ATAS is selected. ? I use a mag loop antenna on my FT897 regularly, which has a primary loop connected directly across the coax, and have no problem with it and its circuitry is basically the same as the 857. Hence I don¡¯t think the matching section on your 6 m antenna has been the cause of the problem and I think I would start looking elsewhere. ? Maybe you can literally ¡°sniff out¡± where the smoke escaped from or find the burnt component to get an idea where the problem is ? Good luck with it. ? 73¡.Eric VK2VE. ? From: [email protected] <[email protected]> On Behalf Of Zack Widup
Sent: Tuesday, 19 July 2022 13:27 To: [email protected] Subject: Re: [FT-857] CQWW VHF ? That could be. I did come to realize something. My 6 meter Yagi has a hairpin match across the input - and the coax. At DC, that would look like a short to whatever the coax is connected to. If the radio was trying to put 12 volts on the 6 meter antenna line, it would've been shorted. I can't figure out what was damaged, though. Q3006 is good. The inductors between the Q3006 collector and the HF antenna connector are OK. When I try to transmit now, there is 12 volts on the emitter of Q3006, but it doesn't turn on 12 volts to the ANT line. If it was doing that before, something was damaged. ? I did verify that all the the final output transistors are OK and that there is RF drive at the correct frequencies from the MAIN board to the PA board.? The? final output transistors have 12 volts on their collectors and, on transmit, have the correct bias voltages on the base terminals. I can't figure out yet why there's no output. ? 73, Zack W9SZ ? On Mon, Jul 18, 2022 at 8:09 PM Eric van de Weyer <groups.io@...> wrote:
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