Duty cycle adjustment for 40 meters

[W9BHI]

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.

[vk3alk]

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

[DMOD]

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

[W9BHI]

Will this circuit work at 7 Mhz?

[DMOD]

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