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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. Title: Re: Duty cycle adjustment for 40 meters Post by: W9BHI on May 05, 2025, 10:30:03 AM Steve, Here is the circuit that I use. It is the same as yours with a few embellishments. The 160/80 duty cycle adjustment works but the 40 doesn't. Here is the schematic.
Title: Re: Duty cycle adjustment for 40 meters Post by: steve_qix on August 05, 2025, 08:24:04 AM I will have to look at my 40 meter A to D converter and see what I did :-) AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
It definitely works, and I use it all the time on 40 meters. But, I think I had to make some minor modifications to the circuit. Also, not all components are created equally. I have found that variations in the input inverter IC can cause anomalies, particularly on 40 meters. I think I worked around these component issues, but I do have to go look at the converter and see exactly what I did. Interestingly, I get 300 watts of carrier output using 4 FQA11N90 on 40 meters. Running 45V @ 7.7 amperes (at carrier). |