Lots of progress to report on the 1712 rig.
With just two TIA amps (one on either side of the 10 pole filter) and the AF amplifiers, I now have it inhaling on 17 meters. But nothing heard so-far on 12. On both bands I can hear the band noise, but just barely. So I may try some RF amplification ahead of the mixer. What do you guys think about this? I think the two TIAs and the crystal filter are providing 30 db of gain.
I want to get the receiver circuitry working well on both bands before I build the T/R and transmit amplifier circuitry.
It is nice to have a project on the bench!
I am trying to find a shaft extender or adapter for that big beautiful HT-37 main tuning cap. The shaft on the capacitor has a width of 1 cm or 0.393701 inches. I need something that will grab onto that and allow for the connection of a tuning knob. Please search your junk boxes!
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Dear Bill: I have a quarter-inch to quarter-inch shaft extender/isolator which would work if you could drill out one end with a drill bit the same diameter as your shaft. Max diameter would be about 0.32 inches. However, if you let us know the shaft diameter maybe someone has an exact-size adapter...
ReplyDelete72,
Walter KA4KXX Orlando, FL
Thanks Walter. This is all a reminder of my need for a digital caliper. I pulled out my ruler and measured a shaft diameter of 1 cm or 0.393701 inches. I hope the IBEW can find something in their collective junk box. 73 Bill
ReplyDeleteBill, if the collective junk box doesn't come through, there is always McMaster
ReplyDeletehttps://www.mcmaster.com/shaft-reducers/
the step-down shaft adapters seem to be just what is called for, but they are a bit spendy. Maybe one of the simple rigid couplers and some hobby store brass shaft would suffice. Or in the spirit of our hobby, I would be happy to try and make something suitable on my 3D printer. 73, Roy
Dear Bill: Another idea is to cut off a one inch length of a 3/4 inch diameter wooden dowel
ReplyDeleteand drill a 1/4 inch hole through the center end-to-end. Then enlarge half of the hole with the nearest drill size to .393 and glue a 1/4 inch dowel in one end for the knob and glue VFO shaft to the other. Then paint it silver so everybody thinks you welded it!
--Walter in Orlando
Looking good their Bill.
ReplyDeleteYou mentioned reference to a book on filters wate is it?
Good DX on 17m.
Paul
De HS0ZLQ/G0MIH.
See if you can use an old permanent marker/white board marker casing? Sometimes these are moulded for the tip and body with different diameters. They are also easy to cut with a pipe-cutter instead of a junior hacksaw. Another reason not to throw things away!
ReplyDelete...Plus.. gentle heat from a heat gun will allow them to be enlarged a little.
ReplyDeleteNote to All: In this video Bill mentions the bandpass filters described in section 3.14 of the EMRFD book, which I do not own, and is out of print again, but amazingly I was able to download a copy from the following website:
ReplyDeletehttps://epdf.pub/queue/experimental-methods-in-rf-design-radio-amateurs-library.html
72, Walter KA4KXX Orlando, FL
Thanks Walter -- I had some trouble with the EMRFD filters on page 3.14. Take a look at the filter for 25 MHz. I built it in the ELSIE software and took a look at the passband scan. It showed a two big peaks and a big dip at the resonant frequency. It was not a flat passband. The EMRFD chart says that these filters are terminated with 50 ohms on both sides. But it looked to me as if the 25 MHz filter would work but only with 500 ohm terminations. I may have been doing something wrong with the ELSIE program -- has anyone else seen a problem with this filter? In the end, I went with Hans Summer's DTC filters -- I used the values from his chart and built one for 12 and one for 17. 73 Bill
ReplyDelete