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Another Homebrew transmitter is being saved.

Discussion in 'Amplitude Modulation' started by N6YW, Feb 24, 2017.

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  1. KM1H

    KM1H Ham Member QRZ Page

    They do make remote controlled automatic tuners these days that can handle close to the so called AM legal limit and for long runs surplus Heliax is very cheap.
    In some percentage of installations OWL may be the only choice.

    The 8JK is 1/8 wave or less spaced and hard to match because of mutual coupling; closed spaced verticals have the same problem. It is also very narrow banded which was fine back in the dark ages when hams stayed within a narrow range of frequencies and had their turf wars daily.
     
    AF6LJ likes this.
  2. W2VW

    W2VW Ham Member QRZ Page

    I wish the problem of a 1000' run of feeder were my problem. I'd even settle for 300'.
     
    AF6LJ, N2EY and KD2ACO like this.
  3. W7TFO

    W7TFO Platinum Subscriber Platinum Subscriber QRZ Page

    Trees? Ice? I'd have to buy both of those to ruin a feedline...

    My elec. co-op suffered some pole failures last monsoon and left over 2K' of #6 hardrawn copper for me to roll up & take.

    Jeez, that stuff is stiff.

    Good fortune acknowledged!
     
    AF6LJ, N2EY and KM1H like this.
  4. KM1H

    KM1H Ham Member QRZ Page

    I took home a few miles of #12 rural telephone wire (single conductor jacketed copperweld) decades ago when this area "modernized". Already on reels and rolled right on my 2 axle car trailer. The two conductor hardrawn version made excellent but heavy reversible Beverages up to 1500' at the old home in town but 500' lower elevation; Im now on top of the highest hill in ~ 20 miles since 1989.

    Good fortune comes to those with their eyes open and a pleasant disposition when begging:D:rolleyes:
     
    AF6LJ likes this.
  5. KM1H

    KM1H Ham Member QRZ Page


    I see what you mean; I grew up on a 90x60 lot as a kid in NY and from then to now Ive been on an acre or more. I almost bought a farm on 21 acres on top of a BIG hill but it was too rural for the wife.
    Now that place is big bucks since the NH NASCAR track is only a few miles away and this area is huge on racing.
     
    AF6LJ and W2VW like this.
  6. KM1H

    KM1H Ham Member QRZ Page

    All you need is two coax fan dipoles at right angles.

    OTOH a small 40-90' tower and a tri or five band yagi or LP and then the fan dipoles for lower bands off the top as inverted V's gives you 9 bands and includes WARCs. Ham heaven without headaches such as unmanageable common mode.

    A relay box at the top and one low loss coax feedline.
     
    AF6LJ likes this.
  7. K4KYV

    K4KYV Subscriber QRZ Page

    If you are running more than three or four quarter-waves of feedline, better to run the OWL flat (no standing waves), rather than as a tuned line (with standing waves). The wavelength error of multiple quarter-waves in tandem as you QSY away from the tuned feedline's natural resonant frequency is cumulative, with the error of each quarter-wave adding up. The result is that the more quarter-waves of tuned line, the sharper the tuning. With too long a length, you can even end up feeding a voltage point at one end of the band, particularly 75/80m, and a current point at the opposite end. If the open wire transmission line is operated flat/untuned/no standing waves, then long lengths of several wavelengths can be very efficient, with little attenuation, and it won't sharpen the tuning. I compared using 140' of RG-213 and RG-214 with 140' of untuned OWL at my installation, and the OWL won out every time, with noticeably higher reading on the RF ammeter at the base of the tower compared to either one of the coaxes, with the same DC input to the transmitter final. Same effect observed on 160 and 80m. I run a flat line from shack to base of the tower but as a tuned feed line from the dog-house at the base, up the tower to the dipole.

    I tried buried coax and regardless of what type I used, even so-called "direct burial", the efficiency dropped steadily after a couple of years use. With fresh coax I got about 92% efficiency, but after a few years it dropped down to approximately 80%. Noticeable causes of deterioration were UV damage to cable exposed to the sun, rodents chewing on buried line, and unexplained deterioration of unchewed direct-burial line. With the untuned OWL, I measured about 98% efficiency.

    The only coax I use in my station now is the transmission line to my beverage receiving antenna. I don't think I'd notice a couple of dBs loss there. Not a sprig of coax or unbalanced line anywhere in my entire transmitting antenna system, except maybe the 160m vertical tee. The insulated vertical tower is fed with a single 8' long #6 copper wire running directly from a tap on the tuning coil to the base of the tower.
     
    Last edited: Mar 5, 2017
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  8. N2EY

    N2EY Premium Subscriber QRZ Page

    Great stuff!

    Just one question:

    What kind(s) of OWL do you use? (I know it's the classic homebrew kind). Wire size, spacing, etc.?

    Thanks

    73 de Jim, N2EY
     
  9. K4KYV

    K4KYV Subscriber QRZ Page

    The OWL running from the shack to the base of the tower is made from #8 copperweld wires spaced approximately 2.5 inches apart. The line running up the tower is #10 copperweld spaced 2" apart. I use ceramic stand-off insulators combined with home-made plexiglass spacers on the line running from shack to tower, held in place 8' off the ground with hot-dip galvanised tee-posts and home-made cross arms. The OWL going up the tower is spaced with EF Johnson 2" ceramic OWL spacers up to the tower, and plexiglass spacers affixed to the tower rungs every 10' up the tower. The OWL runs up through the interior of the tower, spaced to the geometric mid-point of the triangle. In both cases, the calculated Zo is 438 ohms, close enough to 450 ohms for all practical purposes.

    Technically speaking, I don't use a separate antenna coupler with this system. The final stage of the three-stage output network in each of my homebrew transmitters and the modified Gates is remotely located in the dog-house at the base of the tower, remotely controlled using a reversible DC motor/worm drive mechanism, with five separate air variables connected together with shaft couplings. The flat OWL running from shack to tower is merely a link that couples the 2nd stage of the output network to the 3rd and final stage. The resonant OWL running from the 3rd stage up the tower to the antenna, and the single-wire feed from a tap on the tuning coil to the vertical, are the actual antenna transmission lines. The transmitter output terminals are physically located on the rear panel of the dog-house.
     
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  10. N2EY

    N2EY Premium Subscriber QRZ Page

    Thanks for the info! A real low-loss installation!

    73 de Jim, N2EY
     

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