Garry Nichols' 40 Meter CW Receiver

Garry's 40 meter cw receiver

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I was monitoring the CW segment of 40M again this year with a modified version of last year's single MPF-102 regen. I rebuilt it in a more compact form to reduce mechanical instability and body capacity effects. I also added a Bogen audio matching transformer so that I could use my RCA big can sound powered earphones (which use mic elements -- 10 ohms DC each). I decided to use my ham radio 40M inverted L antenna instead of a wire out the second floor window like last year. This antenna is 34 feet long and worked against 16 radials under the sod and a central ground rod.

I wound up coupling the coax from the antenna one turn up from ground on a parallel L/C that was inductively coupled to the tank of the regen. I added the L/C because a one turn coupling coil on the regen's tank worked fine but did not present enough selectivity to reject a powerful domestic religious broadcaster just below 40M. After I added the "passive preselector", I never heard that station again.

This rig is very easy to operate despite its simplicity. It goes into and out of regen very easily, and I don't need to adjust the regen control once set because it only tunes about 55 kHz of the lower end of 40M. If signals are too strong I can reduce coupling by swinging the L/C stage.

The photo was taken after the contest, and I had modified the rig by adding a single stage of audio amplification (having forgotten to take a picture for the contest first!), which gave a very worthwhile improvement in sensitivity and allows me to use lighter coupling from the first L/C. The two RF stages are exactly the same as was used in the contest.

With my sound powered phones, this rig has a very pleasing sound. CW notes are pure sounding and the sonic landscape is seasoned with distant static crashes. I could hear the evening 40M ambient noise level with only the MPF-102. Logging stateside stations was like shooting fish in a barrel (but with some added-in "mental selectivity" needed now and then)! If I do this again next year, I may only log DX stations. It wasn't until I got my log finalized that I realized that I had only copied a single Canadian station. Very curious. Since I listened only evenings, perhaps the skip was long enough not to bring in the rather close-in populated areas of Canada which are just north of me here in central New York, near Syracuse.

Garry Nichols

Garry's 40 meter cw receiver schematic diagram