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   AMATEUR_RADIO      Ham radio for when Armageddon strikes      2,531 messages   

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   Message 337 of 2,531   
   Roy Witt to Ed Vance   
   Resurrected   
   11 Apr 14 14:46:01   
   
   Greetings Ed!   
      
    EV>> The other photo shows that wire points towards the speaker, so I   
    EV>> figure the wire from the RF section has lost the Folded Dipole that   
    EV>> it once had.   
      
    RW>> As I explained above, the red twinlead wire and the red   
    RW>> 'skyryder' are antenna lead-in and wire wrapped iron core   
    RW>> antenna. Rather than run the vertical, I may plug the Skyryder   
    RW>> in and mount the antenna horizontally on the window, which   
    RW>> faces North-by-East. Maybe there's more out there than it   
    RW>> receives on that vertical telescoping antenna. Thanks for the   
    RW>> website URL, I can use the info they have there. But, I'm not   
    RW>> going to join, since $25 isn't my idea of really needing that   
    RW>> info.   
      
    EV> O.K., I sit corrected about that Red Twin-Lead cable.   
      
   You don't need to be corrected. You had it pretty close, considering that   
   you don't have one of these radios at hand to examine.   
      
    EV> I didn't investigate anything else on that web site and didn't know   
    EV> about their request for support was for more than Photos and   
    EV> Schematics of Old Radios.   
      
   Well, there are 3 schematics for that radio on that site. I'd like to have   
   a copy of them, but the radio has a schematic attached to the inside of   
   the back cover and it's readable, with a magnifying glass.   
      
    EV>> A UHF TV Station on Channel 32 came on the air, and I made a Folded   
    EV>> Dipole antenna out of some 300 Ohm Twin-Lead such as what is in the   
    EV>> back of your Hallicrafter Worldwide RX.   
      
    RW>> I've done that before. It works very well. But a log-perodic   
    RW>> would work much better for what I want...all UHF channels,   
    RW>> 14-69 at 40 miles (in Austin)...   
      
    EV>> The Tower was 3 1/2 Miles from our house so I calculated the length   
    EV>> of the antenna was 19 Centimeters, so I cut off enough Twin-Lead so   
    EV>> I could solder the two leads on each end to each other and cut one   
    EV>> wire in the center of the antenna to connected some 300 Ohm wire to   
    EV>> it, the other end went to a UHF TV Convertor we got.   
      
    RW>> If it was that close, a long wire would have worked just as   
    RW>> well. But at least you got some antenna mathematics and   
    RW>> building practice. BTW, that should have been 19 inches...I   
    RW>> have come up with a formula to make 1/4 wave GPs and   
    RW>> multiplying the answer by 4 gives me the a closer length to   
    RW>> build a full wavelength dipole; 2808/Freq in MHz = 1/4 wave...I   
    RW>> also use 2880 to give a 5% extra length to the GP radials...The   
    RW>> antennas I used to build went to the local San Diego HRO store   
    RW>> and sold out within a few days.  They always displayed a flat   
    RW>> 1.2:1 SWR across the band they were designed for.   
      
    EV> I don't think I even had heard of a Log Periodic Antenna in the early   
    EV> to mid 1960's.   
      
   Ummmm. They were on every rooftop of houses with a TV set. Most of them   
   were dual banders, aka VHF and UHF...when I worked for Solar Turbines in   
   San Diego c1967, a younger friend and I built a few for our own use. He   
   was a tool & die apprentice, I was t&d journeyman at the time and he lived   
   two blocks down the street from me.   
      
    EV> But a Twin-Lead LPA would be OverKill for 3.5 miles.   
      
   No doubt, but it could be used to receive other stations within 25 miles.   
      
    EV> And it would be a bear to make and position by the TV Set.   
      
   There's a video on YouTube showing how to make one out of stripped RG59   
   coax (using the shield only) as the electrical 'boom' and #12 house wire   
   as the radials. It is only 58cm (22.6") long. The support boom is made out   
   of wood, 1" square, and all radials are wood screwed to the coax boom at a   
   specified spacing.  Crude, but affective. The video shows the builder   
   holding the antenna pointing it out of the window, waving it about, the TV   
   HD signal fades and brightens as he finds the station's xmitter site.   
      
    EV> Also since it was the 2nd TV Station to be on a UHF Frequency in my   
    EV> area, (the 1st one stopped broadcasting in early 1960), I didn't need   
    EV> a broadband antenna back then, so the antenna worked O.K. for the   
    EV> only one that was in town on UHF back then.   
      
   No doubt. And if that's all there was, it was all that you needed.   
      
    EV> I can't remember when the Local School System started their TV   
    EV> Station on Channel 15 around here. And it was several years later   
    EV> before another Commercial TV station came on the Air here, and then   
    EV> Everybody had TV Stations on UHF!   
      
   Same thing happened to the VHF station where I lived in Illinois. I forget   
   what channels they used, but it eventually went to UHF too. The earliest   
   and best station there was WREX (ch13) in Rockford, another in Daventport,   
   IA (ch6) and one in Madison, WS (forget its channel). Those were VHF and   
   about 30-40 air miles away. And of course, all of the Chicago stations   
   were about 90-100 miles away. WGN, WLS, etc.. but they required long, long   
   with many radial antennas.   
      
    EV> We've only have had two VHF stations, and both of them came on the   
    EV> Air way before any UHF stations did.   
      
    EV> I looked at the book I used back then to calculate the length of   
    EV> Twin-Lead I'd have to cut and one chart says TV Channel 32 back then   
    EV> was 578-584 Mc/s.   
      
   Which isn't the case today. The HD mode today doesn't use that much   
   spectrum. Part of that spectrum was for the video and part is for the FM   
   audio signal.   
      
    EV> I looked at another chart in the book to find the wavelength was   
    EV> about 52 Centimeters, Half of that is about 26 CM , or about 10.25   
    EV> Inches.   
      
   Which falls within the measurements given for the 582MHZ LPA...   
      
    EV> Tonight I looked at a ruler and that seems about the length that I   
    EV> recall the antenna being.   
      
    EV> My 19 CM guess earlier was way off the mark, wasn't it? .... ..   
      
   Yes, it should have been about 19 1/4 inches.   
      
    EV> I do the best I can with what I got, but when I really want to know   
    EV> something I go to the Books I have to get it down to the nitty   
    EV> gritty.   
      
   I keep a formula in my head that allows me to figure a 1/4 wave antenna.   
   Multiplying that by 4 and you get the full wave length.   
      
   2808/freq in MHz * 4 = a full wavelength.   
      
   2808/582 = 4.825 x 4 = 19.24"   
      
   Somebody asked me some years ago in the HAM echo where I got that 2808   
   number. Which had something to do with figuring the length of a dipole and   
   a number around 5600. It's been so long since I figured that, I have   
   forgotten what it was.  Anyway, building 1/4 wave GPs that 2808 number   
   worked out very well, as each one of those antennas made for 450 MHz, had   
   less than 1.2:1 VSWR across the entire 10MHz of that band. As would be   
   expected, the 145Mhz and 220Mhz antennas worked just as well.   
      
    EV>> A neighbor across the street heard about the TV Channel 32 antenna   
    EV>> that I made and asked me to make one for them too, I had GOBS of   
    EV>> wire so I made one for them.   
      
    RW>> Believe it or not, that also works as a CB antenna, which is my   
    RW>> very first antenna fabrication. The next one was an all wire   
    RW>> ground plane, that was mounted outside my 'radio room' on the   
    RW>> second floor of our apartment, c1960?...   
      
    EV> I ran a wire around my radio room up near the ceiling, One Big Loop.   
    EV> I used  it with the DX-40 on 20 Meters.   
      
   Not for transmitting I hope.   
      
    EV> -snip-   
      
    RW>>> That was illegal for a CBer to do, but we did the same thing.   
    RW>>> It sure beat looking through a pile of xtals and wasting time   
    RW>>> making the change.   
      
    EV>> Plus the switch box kept you from opening the case to change a Xtal.   
    EV>> -snip-   
      
    RW>> Actually, the 11mtr lunch box had a xtal socket on the outside   
    RW>> face of the radio, allowing xtal changes on the fly. It was a   
    RW>> cumbersome job of keeping track of those umpteen xtals, so we   
    RW>> fixed that.   
      
    EV> Oh, O.K., Thanks Roy!   
      
   Not only that, but the radio was xtal controlled xmit only. It had a   
   tunable receiver. That was nice for listening to off frequency radios.   
   My Golden Eagle had that too, but it could switch to a set of 23ch mixer   
   controlled receiver too.   
      
            R\%/itt - K5RXT   
      
    On Ward's exalted throne, he is still seated on nothing but his big arse.   
      
      
      
   --- GoldED+/W32 1.1.5-31012   
   --- D'Bridge 3.99   
    * Origin: HAM Radio, aka Amateur Radio. 804? Over! (1:387/22)   

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