[R-390] Antenna question

Thu, 18 Jul 2002 12:35:23 -0600

Hi have used Hy-Gain BN-86 baluns to feed the balanced input through the matching Amphenol Twin Ax connector with excelent results for years... aligning the balanced transformers using the same method as described in the R-390 non"A" manual is crucial. Aligning the input using a pair of 62
ohm resisitors fed from the URM-25 . to each of the balanced input connectors. The center conductor goes the the junction of the resistors, and the ground lead goes to the chassis.... It works every time for me... 73 de Jordan...

"Scott, Barry (Clyde B)" wrote:

> I'd like to try this.  Curious about a few things, though.
>
> 1.  Isn't the impedence of a plain-old dipole somewhere near 50 - 75 ohms instead of 150?  I realize this isn't too bad for a receiver, but just wondering if there's a way to get a better match.  I know a folded dipole makes for about 300-ohms at the feedpoint, but that's not much better.
>
> 2.  Not familiar with CAT5.  Is it possible to take some good, insulated wire (I have a large spool of 26-ish gauge, stranded, teflon coated wire -- good quality stuff) and twist my own twisted pair?  Something along the lines of 2 to 4 twists per inch maybe?
>
> Thanks for the suggestion.  I would like to have a separate receiving antenna so I can run my xcvr without changing the antenna everytime.
>
> Barry(III)- N4BUQ
>
> > -----Original Message-----
> > From: Thomas W Leiper [mailto:[email protected]]
> > Sent: Thursday, July 18, 2002 11:39 AM
> > To: [email protected]
> > Subject: Re: [R-390] Antenna question
> >
> >
> > On Thu, 18 Jul 2002 08:20:26 -0500 "Scott, Barry (Clyde B)"
> > <[email protected]> writes:
> > > What is/was the recommended "standard" antenna and feedline for the
> > > R390A?
> >
> > There is no recommended standard because the radio was
> > used in so many applications. The only installation documentation
> > I have ever seen showed unbalanced was for whip antennas and
> > the balanced for a doublet (if you are under fifty read "dipole")
> > fed with twisted pair. I use twisted pair and even CAT5 cable
> > with multiple dipoles and get excellent results with good zeroing
> > of the antenna tuner on all bands. The twisted pair also has the
> > added (and primary) advantage of making the antenna system
> > immune from noise not detected by the antenna elements, such
> > as the PC computers in the shack that everybody is always
> > complaining about, because twisted pairs cancel out induced
> > currents...which is why the phone company can smash thousands
> > of them together in a bundle, and why your CAT 5 cable works
> > at 100 Mhz without any shielding...imagine that.
> >
> > Running an unbalanced feedline invites local noise, and using a
> > balun to then feed it into the balanced input accomplishes nothing
> > more than adding more loss and yet another tuned artifact into the
> > system. If you really want the extra stage gain on the unbalanced
> > input, do the Navy mod, which grounds one side of the balanced
> > input (making it unbalanced) and feeding the other side out the
> > unbalanced bulkhead connector. That gives you an unbalanced
> > 75 ohm system which not only allows you to use cheap TV coax
> > like RG-59 or RG-11, but also just happens to be the impedance
> > at the feedpoint of a resonant half wave dipole.
> >
> > WOW...Isn't that exciting? Now, listen to this...magnified ninety
> > two thousand times, the sound of the viscious Afgan panther lizard
> > visiting the chemist...
> >
> > Twisted Twit Hammarlund
> >
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