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Possible QMX/QDX PA Improvement Idea

mux_folder2001 All Messages By This Member #142394 It occurred to me that the Interface between the ACT08 drivers and the BS170 gates could be AC coupled. A quick simulation with 100nf and a 2k to ground on the gates shows no ill effects. The advantage is two-fold. First, a BS170 failure that puts 12V on the gates is less likely to damage the ACT08 outputs. Second, any failure that leaves the ACT08 outputs high for a long time is less likely to fry the BS170s.? ? Just a thought. ? Tony AD0VC
Jerry Gaffke All Messages By This Member #142397 Good idea! Though I'd think a DC bias at the gates of 0v would mean the 5v swing? is now going from -2.5v to +2.5v, not enough to fully turn on the BS170's. Perhaps that 2k should go to 2.5v when TX is true, and to 0v when TX is false. Getting a bit more complicated. ? Could go to a solid 2.5v rail, except that Hans has found reason to keep the? DC supply to the final on during receive. ? Jerry, KE7ER ? ? On Thu, Apr 3, 2025 at 05:53 AM, mux_folder2001 wrote: toggle quoted message Show quoted text It occurred to me that the Interface between the ACT08 drivers and the BS170 gates could be AC coupled. A quick simulation with 100nf and a 2k to ground on the gates shows no ill effects. The advantage is two-fold. First, a BS170 failure that puts 12V on the gates is less likely to damage the ACT08 outputs. Second, any failure that leaves the ACT08 outputs high for a long time is less likely to fry the BS170s.? ? Just a thought.
Hans Summers All Messages By This Member #142400 Hi Tony In my experience, practically there are undesirable effects including loss of bandwidth (meaning reduced power at higher frequencies), lower power output and lower efficiency. It's my opinion that AC coupling would cause more problems than it would solve.? 73 Hans G0UPL toggle quoted message Show quoted text On Thu, Apr 3, 2025, 14:53 mux_folder2001 via <canthony15=[email protected]> wrote: It occurred to me that the Interface between the ACT08 drivers and the BS170 gates could be AC coupled. A quick simulation with 100nf and a 2k to ground on the gates shows no ill effects. The advantage is two-fold. First, a BS170 failure that puts 12V on the gates is less likely to damage the ACT08 outputs. Second, any failure that leaves the ACT08 outputs high for a long time is less likely to fry the BS170s.? ? Just a thought. ? Tony AD0VC
mux_folder2001 All Messages By This Member #142403 开云体育 Yes, probably so. Still, I might play with the idea a bit more. It's all part of the fun. Tony AD0VC toggle quoted message Show quoted text From: [email protected] <[email protected]> on behalf of Hans Summers via groups.io <hans.summers@...> Sent: Thursday, April 3, 2025 7:35 AM To: [email protected] Notification <[email protected]> Subject: Re: [QRPLabs] Possible QMX/QDX PA Improvement Idea ? Hi Tony In my experience, practically there are undesirable effects including loss of bandwidth (meaning reduced power at higher frequencies), lower power output and lower efficiency. It's my opinion that AC coupling would cause more problems than it would solve.? 73 Hans G0UPL On Thu, Apr 3, 2025, 14:53 mux_folder2001 via <canthony15=[email protected]> wrote: It occurred to me that the Interface between the ACT08 drivers and the BS170 gates could be AC coupled. A quick simulation with 100nf and a 2k to ground on the gates shows no ill effects. The advantage is two-fold. First, a BS170 failure that puts 12V on the gates is less likely to damage the ACT08 outputs. Second, any failure that leaves the ACT08 outputs high for a long time is less likely to fry the BS170s.? ? Just a thought. ? Tony AD0VC
mux_folder2001 All Messages By This Member #142404 开云体育 Good point. I probably didn't run the sim long enough for that effect to show up. Tony AD0VC toggle quoted message Show quoted text From: [email protected] <[email protected]> on behalf of Jerry Gaffke via groups.io <jgaffke@...> Sent: Thursday, April 3, 2025 7:13 AM To: [email protected] <[email protected]> Subject: Re: [QRPLabs] Possible QMX/QDX PA Improvement Idea ? Good idea! Though I'd think a DC bias at the gates of 0v would mean the 5v swing? is now going from -2.5v to +2.5v, not enough to fully turn on the BS170's. Perhaps that 2k should go to 2.5v when TX is true, and to 0v when TX is false. Getting a bit more complicated. ? Could go to a solid 2.5v rail, except that Hans has found reason to keep the? DC supply to the final on during receive. ? Jerry, KE7ER ? ? On Thu, Apr 3, 2025 at 05:53 AM, mux_folder2001 wrote: It occurred to me that the Interface between the ACT08 drivers and the BS170 gates could be AC coupled. A quick simulation with 100nf and a 2k to ground on the gates shows no ill effects. The advantage is two-fold. First, a BS170 failure that puts 12V on the gates is less likely to damage the ACT08 outputs. Second, any failure that leaves the ACT08 outputs high for a long time is less likely to fry the BS170s.? ? Just a thought.

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