The Shack Photo Suite: Go ahead and show off!

Discussion in 'Amplitude Modulation' started by N6YW, Jul 15, 2016.

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  1. K5UJ

    K5UJ Ham Member QRZ Page

    You and me both. This is a common problem with homebrewed rigs. Ham homebrewers don't like to draw schematics apparently. I can guess why: After all the work, they probably figure you got the rig and it works, therefore I am DONE. If I were paying someone to build a rig for me I'd insist on a schematic as part of the deal. I've heard hams say, "Well just ask me if there's a problem." Well, as you and I know, someday, someone will get a nice HB rig and the builder is SK and we are left looking at some part or circuit wondering...."what does that thing do?"

    You all might think it's a plate modulated AM rig and who needs a schematic for that. Well, once you get an old rig built into a rack with wiring harnesses going every which way, and all the wire is the same color jacket, and it's full of mystery relays, keying circuits that don't make sense, stuff that's been changed by previous owners and so on, you'll wish you had a schematic.

    Message to hams who homebrew rigs: You may be making it for yourself, but you won't be around forever and someday someone will get your work. Do them a favor and draw up a schematic and tape it to the inside of the rack.
     
  2. WB5HAK

    WB5HAK Ham Member QRZ Page

    It's not the major "sections" of the rig that worry me about looking around for problems. This one uses good, teflon wiring that seems to have MANY colors to help tracing, so that's not even a real problem. It's the small protective circuits, switching, etc. that are worrisome.

    I love the looks of your rig on QRZ, Rob. Nice catch!! This rig I am breaking in bandswitches 160, 80, 40, 20, 17 and 15M. 10 to 12W of drive is provided by an outboard rig which also provides the VFO signal for the various bands. The speech amp is built into the final/modulator tube compartment and uses 2 metal tubes (6L6 or 6V6). I looked while putting the finals in, but didn't note it at the time, so not sure which. The Volumax 4000A limiter has been modified to run PTT through as well as the audio from an amplified D-104. My wife thought the audio was good on an outboard receiver with headphones, but I am yet to get another ham's opinion of that. Hopefully this evening I can do that.

    Thanks for sharing. I do home that the other VMY rigs are kept going as he was really a first rate builder from the looks of this one. I want to find some nice labels like your rig has, so am on the hunt for a provider of those. Then I need to get to work on a radial system for a nice 160M inverted L or 1/4 wave vertical one. 73,
    Don, WB5HAK
     
  3. K4KYV

    K4KYV Subscriber QRZ Page

    I used to never worry about schematics and circuit diagrams of my homebrew stuff. But I have found that after a few years go by, even I am mystified by some of my own homebrew circuitry, so I have become more and more conscientious about documenting my work. I haven't felt like going back and laboriously tracing out all the wiring in everything I own, but whenever I have a problem and have to trace out something, I draw out the circuit and label it in a notebook dedicated to the purpose. I have a separate notebook for the antenna system, the modified BC transmitter, my homebrew transmitters and station controls. This has helped me tremendously, and would help anyone who succeeded me. It still needs to be organised and categorised better, since a stranger would have to carefully study my documentation to sort it all out.

    Metal 6L6s are physically larger than metal 6V6s. If you are not sure, look up the tube data and you may be able to figure it out without having to pull the tubes out or pulling the modulator out of the rack.
    http://www.tubedata.org/

    I'm pretty sure it was you I heard Sunday evening on 3890 in QSO with K9EID and others. The audio was crisp and clean, but I could still detect a slight distortion and the lows were lacking. I suspect the culprit is the amplified D-104. The built-in stock pre-amp in the base of the microphone is a piece of crap, originally designed by the manufacturer to turn the D-104 into a CB "power mic". There are much better homebrew versions on various websites, including this one (he has a lot of other interesting stuff on his QRZ page; scroll a little more than halfway down):
    ASTATIC D104 MODIFICATIONS - D104 PREAMP - D104 BUFFER CIRCUITS

    You don't have to do up the fancy circuit board; the circuit is simple enough that point-to-point wiring on a piece of perf-board will work fine. Do a Google search for "substitute d-104 preamplifier" and you will find many more circuits. I use an unamplified version of the D-104 feeding a pre-amp that puts 20 megohms of load on the microphone. Astatic recommended a minimum of 5 megohms of load, and 10 will work better. Many of the 1950s-60s vintage AM ham rigs placed anywhere from 50k to a couple of megohms load across the mic input; this will kill the low frequency response of a crystal microphone element like the one in the D-104. With upwards of 10 megohms of load or more, the mic works a lot better, but certain precautions must be observed. A complete write-up of my microphone and pre-amp appears in the November 2014 issue of Electric Radio.

    I'm not sure what your Volumax limiter has to do with the PTT function, but I use an extra relay hooked up to the T/R system to mute the audio feeding into my compressor/peak-limiter unit when I'm not transmitting. My unit is a UREI BL-40 Modulimiter, which uses an optical device for compression (they call it "RMS limiting"); those have a limited service life since an incandescent bulb is used to control a photo-transistor, so I mute extraneous shack noise and receiver audio pick-up when not transmitting, to prolong life of that module. I have an extra one I have never tested as a spare, but I want to keep the original running as long as possible. Last time I checked, after-market replacement modules cost at least $100 apiece with no guarantee that they would work the same as the original.

    Now you're talking. I'd recommend a minimum of 30 quarter-wave radials and ideally 60 or more. A full 120 might be overkill, for an extra fraction of a dB, but will add redundancy in case some radials get damaged by physical trauma or corrosion and the system will likely last longer. Otherwise, lay down as many as you have room for, and make each one as long as possible. For the same amount of wire, a large number of shorter radials is better than 4 or 5 full-length 1/4λ ones. The more radials you have down, the more effective longer length becomes.
     
  4. WB5HAK

    WB5HAK Ham Member QRZ Page

    Don,
    Yes, that was me with K9EID and others last night. You had a really nice signal into SW Oklahoma. If I hadn't already turned the transmitter on, I would have hung around and called you. I knew Bob needed to go, but I could have stayed a bit.

    Thanks for the audio report, and you are SPOT on. It did come with an amplified D-104, which I also detest. You saved me asking where I had seen your article on your D-104, so I'll dig out November, 2014 ER Magazine and give it a read and fix this one. I don't like using amplified mics, so that was on the list of things to do either fix this one or wire the stock D-104 I use with a Viking II to work with the transmitter.

    What I meant about the Volumax was that N4VMY modded the unit with a 4 pin socket so audio and PTT is automatically routed through it to the transmiter through the same cabling. I will pull the speech amp out soon and trace it out to see what he used on the input of it and correct accordingly. It would be nice to know anyway.

    Thanks for all the suggestions. I do really appreciate it and as I learn more, I may ask more.
    73,
    Don, WB5HAK
     
  5. WB5HAK

    WB5HAK Ham Member QRZ Page

    Oops, I meant "transmitter OFF, vice on". Darned human spell check.
    Don
     
  6. K4KYV

    K4KYV Subscriber QRZ Page

    OK, I see. That was for a mic - T/R switch combination, like the D-104 and G-stand, or a hand mic to plug into the Volumax and carry the T/R relay circuit as well. I have about the same opinion of hand mics and desk mics as I do of amplified microphones. It's not a matter of if, but when the desk mic will get knocked off the table and crash to the floor. See my solution to the T/R problem in my write-up in this month's ER, describing my hand-held T/R switch.
     
  7. K5UJ

    K5UJ Ham Member QRZ Page

    If you have the kind of D104 head that threads on to a stand, i.e. doesn't have that G stand plug built into it, and you can't find a mic boom or don't want to drill holes in a desk top, then take a trip to a music store, not a real music store that sells music, but one of those strip mall places that sell guitars, amps, and other garage band gear, and get a floor stand for a microphone. The D1o4 should thread on to it and you can position it in front of you, or tilt it over with one hand if you want to get closer to it to cut out background noise. Use in conjunction with a hand held toggle T/R switch.
     
  8. K4KYV

    K4KYV Subscriber QRZ Page

    Mine was made from an ancient desk lamp boom that originally clamped to the edge of the table. I re-purposed it to make a mic boom, because when I used it to hold the workbench lamp, I was always bumping my head on the damned thing and was tempted more than once to smash it to smithereens. I was able to clamp it to one of the side rails of my audio rack, and fabricated a mounting bushing to hold the D-104. My D-104 pre-dates the G-stand, and it is mounted in a small ring, using flexible fibre cord instead of springs. The home-made bushing attaches the ring to the old lamp boom.

    Some of the hardware used with old style incandescent lamps is exactly the same and threads perfectly to some sizes of microphone mounting hardware.
     
  9. WB5HAK

    WB5HAK Ham Member QRZ Page

    Don,
    What kind of wire do you suggest?? Looking at my locations for a good inverted L, I am pretty sure I can get easily 100' to full 1.4 wave lengths. One location, of course the one with the most room, is 300' or so from the house, so I may opt to use the closer location to keep from needing to use low loss line to reduce feed line losses. As I check copper wire prices, "sticker shock" comes in VERY quickly. One can put $600 in good, insulated wire plus staples to hold it to the ground until the grass grows around it, etc. SURE raises the cost of a good radial system. Now, has anyone had any success with 14 gauge electric fencing wire?? That stuff is about $45 for a HALF MILE, so much more affordable, IF it will work and last long enough on the ground to justify all that work.

    If not, I'll just buy enough good, copper wire to put out what radials I can and add to the number as I can afford it on a fixed income. Thanks for what you have experienced, and comments from any others with ideas. I knew copper has gone up, but I guess I've been using dipole wire from an old "stash" and didn't realize just how much it had gone up. Smaller gauge copper clad steel wire is much cheaper if that's another alternative. I have heard in the past that it didn't last long in the ground, however.
    73,
    Don, WB5HAK
     
  10. K4KYV

    K4KYV Subscriber QRZ Page

    I would use solid wire, not stranded. It will last longer. It doesn't matter whether it is insulated or bare, but the insulated stuff should last longer in corrosive soil, since it is protected by the plastic insulation. If you could find a roll of solid soft-drawn bare copper, that might be the cheapest, but lately I have found that certain sizes of bare copper wire are hard to find. I used #12 for mine, although #14 would probably be OK and last a long time. I once used copperweld in a radial system; it was some old railway telegraph wire with a heavy copper sheath, made to withstand the corrosive smoke and fumes from steam locomotives, that I picked up for free. I still occasionally dig a piece up, and it has survived remarkably well. But eventually the copper sheath will corrode away, and then the deterioration of the steel will be very rapid. Some time ago I saw in a broadcast rag some company was selling soft-drawn copperweld, made specifically for radial systems to discourage copper thieves. Soft drawn, they said it isn't springy, which makes it easier to lay.

    Look for scrap wire or wire anywhere you can find it. Sometimes you can still get it for free. In that case, I'd use anything I could get and not be too picky. I bought the wire for my radial system back in 1974, a 16,000 ft reel of #12 solid soft-drawn bare copper, for $400. Cut into 120 pieces, each radial is 133' 4" long.
     

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