Heathkit box + more

[Robert Myers]

Steve,

Does this contribute to RFI that may be experienced by any neighbours (I mean by NOT using a BALUN)?  Whether the BALUN is (1:1:), or say (3:1) --- and even when the SWR shows as being quite good WITHOUT a BALUN in place?

Suppose my antenna is an inverted "V," and that it is pretty close to 50 Ohms (down from its 72 Ohms) due to its adjusted slope.  Should you still use a (1:1) BALUN?   You are still going from the coax (UN) to the inverted "V" (BAL), so maybe you should put in a BALUN anyway?.   But why?  (Again, with emphasis on how this relates to any RFI --- if at all.)

If you are having slight RFI problems with neighbours, is the addition of a BALUN a possible solution --- I mean does it "in theory," at least, cause a few dB less interference?  What's the physics/electrical engineering behind it?  It certainly wouldn't hurt, would it?  (Would it?)

I hear a lot of anecdotes (and I'm sure they are all quite true for the particular case they stem from), but I wound like to hear some theory referred to, if possible (just to help me perhaps), as to why there's a need for a BALUN, and/or why it works, etc., or when would it really NOT matter at all, perhaps  (if such a conditions even exists) ----again, with some electrical engineering theory from someone who understands what's going on from that standpoint.

Thanks,
--- Rob

"Stephen C. Finch" wrote:

> Martin,
>
> IMO using a balun is always advisable when transmitting from a dipole.  If
> the dipole is flat, then the theoretical impedance is 72 ohms.  If the legs
> slope, the impedance will decrease with 90 to 120 degrees between the legs
> giving 50- ohms or so.  So for impedance matching, no balun would be
> necessary.
>
> However, if a coax is attached directly to a dipole, it is more common than
> not that currents will flow in the outer jacket to the coax due to the
> mismatch between the dipole and the antenna.  These currents several affect
> the antenna pattern and cause the SWR to go "haywire." This is primarily due
> to the fact that a dipole is a balanced antenna and the coax is an
> unbalanced transmission line.  Thus the balun  ("bal"anced to "un" balanced)
> will transform the balanced dipole to the unbalanced coax.
>
> There are two types of baluns - current and voltage.  I prefer the current
> baluns as they are constructed to eliminate the outer-shield currents.  Two
> good books are very insightful into this topic:  "Reflections II" by M.
> Walter Maxwell and "Building and Using Baluns and Ununs" by Jerry Sevik.
> Both are terrific additions to a ham's library.  I especially like
> Reflections II as it describes and debunks many antenna, transmissions line,
> and antenna tuner myths.
>
> Steve Finch
> AIØW
>
> -----Original Message-----
> From: Heathkit Owners and Collectors List [mailto:HEATH at LISTSERV.TEMPE.GOV]
> On Behalf Of George R. Griesbach W5GRG
> Sent: Saturday, December 25, 2004 8:01 PM
> To: HEATH at LISTSERV.TEMPE.GOV
> Subject: FS: Heathkit box + more
>
>  I was rummaging around in a shop I frequent and found a large Heathkit box
> approx 24x24x12h. No Heathkit inside, but there was a complete G scale Emmit
> Kelly Circus Train set by Bachman, steam locomotive+tender+ 3 cars+ track
> and PS and misc acc.  I set it up under my tree, runs great. I will put it
> all back in the box and sell all for $150.00+ shipping from 78013.
> I also have some other Heathkit stuff on my website FS.
> pics
> http://www.comforttexas.net/gallery
> Thank You
> George R. Griesbach W5GRG
> 505 River Oaks Rd.
> Comfort, Texas 78013
> w5grg at comforttexas.net
> http://www.comforttexas.net/w5grg
> ---
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parties involved.  This list and the City of Tempe are not responsible
for losses or misrepresentations of any kind.  Buyer beware!

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