This little box-in-progress is a 40/20 meter CW rig for portable use, based on the miniR2 receiver circuit. The circuitry is similar to that described in the home station, but built compactly in one box. It's being built "ugly" style (but if done neatly it's actually "pretty ugly" :-) inside). I resolved to try a number of substitutions to avoid big orders for new parts!
The miniR2 is KK7B's reworking of the R2 for portable use -- no speaker
audio power amp, simpler input networks, and a few other changes for the
better which actually can be incorporated into the original R2.
| VFO | 7-7.2 MHz, built in a small shielded box. The Hartley circuit, similar to that used for the W7EL Optimized QRP Xcvr, is implemented with surface mount chip caps, and two other buffer stages are built on the sides of the box. A doubler is switched in for 20 meters -- two miniature 4PDT slide switches do the band switching. A Jackson Brothers ball drive is used -- the one that is basically 6:1, but for a half-turn acts as a vernier at 30:1. And it's temperature compensated -- details here. |
| RIT | Same as my other rig, except just a pushbutton to temporarily disable it for spotting. |
| Transmit chain | 2N2222A/2N3553/NTE236(=MRF475), 2N2907 keying transistor. (I found the 2N3866 driver specified in material like DeMaw’s books insufficient to drive my broadband output stage with feedback to a full 5+ watts. Don’t ask me why!) Another 4PDT slide switch to change the lowpass filters and TR switch series tank circuit. Dead-bugged on a board mounted to the back of the box, and on the slide switches. This gives me a maximum of 9 watts on 40, about 6-7 watts on 20, though I drive it so each band is at 5 watts at 13.8 volts. A pot is available on the doubler bandswitch to reduce the 40m power to be equal to 20. |
| MiniR2 | dead-bugged on a board mounted to the bottom of the box. A 1 kHz CW lowpass filter used, as in the R1/R2 descriptions in the articles, with a smaller .47 uF series coupling capacitor to help with low-frequency rolloff. Filter can be bypassed, with a "broad" setting limited by a .47 uF series capacitor, and a .47 uF shunt cap. Left out the highpass filter with the 120 mH inductor... someday a sharper highpass filter would be nice, meanwhile the low-end rolloff with smaller coupling capacitors at any 500-ohm point works pretty well in a CW-only rig... the 1.2 mH inductors are 37 turns #28 on FT-37-72's. |
More to come...
Spent time in the cabins testing out the rig and trying to know what to expect with various wire antennas. The rig was my homebrew 4-watt 40/20 meter CW job based on the miniR2 receiver. My results were not quite as promising as I had hoped, but of course I was used to my big 350-foot horizontal loop at home. A 50-foot random wire was the cabin antenna, with an SPC tuner circuit.
A test expedition (day hike) to Leveaux Mountain didn't do too well either. Height was great, but the 40 meter delta loop didn't work too well on either 40 or 20. Not only that, I fell on the way down and the battery (Yuasa 10 AH) was damamged -- top broke out of one cell. It still worked OK at home, so I decided to just epoxy the top and see what happened.
On FD, I hiked about 2 miles from Cascade River State Park to Lookout Mountain hike-in campsite. It is on the famous Superior Hiking Trail, so had lots of day hikers (no long distance ones) pass by on their way to the nice little overlook. The site was pretty deluxe, with an outhouse, shelter, and picnic table. Got there about 3 pm (CDT), and was on the air at 2137Z, with the wire for the delta loop now turned into a long dipole. I was not doing too well on 40 or 20... 22 contacts in 4 hours... but then I dug out my wire roll and put up a 13-foot quarter-wave wire with quarter-wave ground counterpoise... and suddenly I felt I was actually heard! Then got 29 contacts in 2 hours on 20 meters, pretty good considering I took lots of breaks to watch the sunset. Somewhere along the way, the battery started to give out (damage, plus I hadn't really charged it all the way) but I was still putting out something (2 watts?). A few 40 meter contacts for a half hour (dipole wire fed as flat-top with a quarter-wave counterpoise wire) then it was time for bed.
A quick half-hour in the morning on 40 meters got me six contacts -- I was down to 1 watt now as the battery petered out... but then had to pack up because the rest of the family had to check out of the cabins!
Some later operating when camping closer to the water got me some pretty solid contacts with a 27-foot wire sloping into the trees, and a 1/4 wave ground wire for each band. Wonder if the waterside or the mountaintop would end up better?
My whopping big total: approx. 6-1/2 hours of operation 40 meters: 25 contacts 9 sections 20 meters: 38 contacts 27 sections
Meanwhile, I was happy with the rig that nothing shook loose inside (all dead-bug construction), and that it would still play down to 9 volts (as tested in the shop). VFO drift was of course worse in the field, especially if left out overnight then run in the morning as the sun hit it!
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