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THE AM BULLETIN BOARD => Class E Forum => Topic started by: W9BHI on January 05, 2025, 11:30:48 AM



Title: Duty cycle adjustment for 40 meters
Post by: W9BHI on January 05, 2025, 11:30:48 AM
Anyone have a circuit for changing the duty cycle of the square wave output on the driver on 40 meters? The one Steve (QIX) uses won't work at 7Mhz.


Title: Re: Duty cycle adjustment for 40 meters
Post by: vk3alk on January 05, 2025, 05:08:35 PM
Hi Don

In the past I found Steve's circuit worked well on 160/80M but didn't have the full range on 40M using the 11N90 FETs....

When I built Nigels 40M VMCD using the CREE FETs it worked well and was able to stretch the Duty Cycle close to 50% which it seemed to like....

Also in the past have applied variable DC bias to the IXDD input.....about 2 -3 volts no more and that changed the DC....but cannot remember whether this was tested on 40M though....

Hope this helps...


Wayne



Title: Re: Duty cycle adjustment for 40 meters
Post by: DMOD on January 09, 2025, 08:59:21 PM
Anyone have a circuit for changing the duty cycle of the square wave output on the driver on 40 meters? The one Steve (QIX) uses won't work at 7Mhz.

Here's a circuit. You may have to tweak C1 and C2.

Phil - AC0OB


Title: Re: Duty cycle adjustment for 40 meters
Post by: W9BHI on January 11, 2025, 09:48:31 AM
Will this circuit work at 7 Mhz?


Title: Re: Duty cycle adjustment for 40 meters
Post by: DMOD on January 13, 2025, 05:43:09 PM
Will this circuit work at 7 Mhz?

Switching frequency of 74ACT74 is up to 210MHz, so yes,

https://www.ti.com/lit/ds/symlink/sn74act74.pdf?ts=1736762340660&ref_url=https%253A%252F%252Fwww.mouser.co.uk%252F


Title: Re: Duty cycle adjustment for 40 meters
Post by: steve_qix on February 08, 2025, 06:46:47 PM
Hmmmmmmm...  I use my circuit on 40 meters, and it works quite well.

It's been a while since I've had to adjust it, and I don't remember if I had to make any circuit value adjustments for 40.  I don't recall making any, but if I did, they were very minor.
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