[Hallicrafters] 40 m antenna used on 80 m - what to expect?

[Carl Nord]

Mike WA4DLF 

Geez-lighten up guy

I shared it as a self effacing story about my view as a scared Novice 40
years ago.

"Life is a whole lot more fun" as you say,  when you pay attention to the
story.



Carl
WA1KPD
Visit My Boatanchor Collection at
http://home.comcast.net/~chnord/wa1kpd.html

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Mike Everette
Sent: Friday, October 03, 2008 2:11 PM
To: Hallicrafters at mailman.qth.net; Carl Nord
Subject: RE: [Hallicrafters] 40 m antenna used on 80 m - what to expect?

Oh my poor achin' pi-net... the blind are leadin' the freakin' blind.

I feel like I'm watchin' an episode of "Home Improveement" with
Tim-the-Tool-Man.

Will someone please get an Antenna Book?  I recommend the older versions,
because the newer ones were somewhat dumbed down to the point that a lot of
basic knowledge was left out.

Take a look at multi-band dipoles, or DOUBLETS, fed with open wire or ladder
line.  Using a TUNER (or as the ARRL terms it, a "transmatch" -- but it's
still a tuner) -- not a balun!  

The 40-meter doublet, fed with about 67 feet of open wire/ladder line, can
be tuned on 80-40-30-20-15-10 meters.  I never tried it on 17 or 12 meters
but it'd probably work.  But you have to use a tuner, not a balun, for it to
work RIGHT.  Think of a tuner as a continuously-variable-ratio,
variable-frequency balun.

A coax-fed antenna is resonant at ONE frequency.  It may be usable over a
wider band of frequencies but they are still fairly close to the resonant
frequency..  The only real out-of-band usability for a coax fed dipole is on
an ODD harmonic.  An 80 meter dipole could be moderately effective on 30
meters, maybe 17 meters, 12 meters; but it won't work on 40 because that is
the second harmonic.  It won't work on 20 either, because that's the fourth
harmonic (an EVEN harmonic); nor will it work on 15 or 10 because those are
also even harmonics.  

Look at the voltage/current distribution in a dipole/doublet... The feed
point impedance will be much greater than 50 ohms on the second harmonic, or
any other even harmonic; and trying to feed it there with coax is somewhat
akin to laying a big resistor across the center insulator -- as in "dummy
load."  If the feed point is at a high VOLTAGE point, the feed point
impedance will be high.  If it's fed at a high CURRENT point (odd harmonic),
the impedance is low.  Depending upon exactly what fundamental frequency the
antenna is cut for, the feed point impedance on an ODD-harmonic higher band
may not be exactly 50 ohms, but it may be close enough to be usable with
coax feed.

No coax fed antenna is going to radiate well -- if at all --at a band lower
than the one it's cut for.  If it ever did, it certainly didn't work 
well!  Had you used a proper antenna, you'd have been amazed!

In fact a light bulb dummy load might get out better.  I've made a few cross
town contacts with a light bulb.  2 miles is great DX on 75 meters, that
way.

Pu-LEEZE get some knowledge.  Life is a whole lot more fun when you are
informed.  And your final tubeage will last a LOT longer; plus you won't
melt the poly-insulation out of your tank coils.

OK, you Tool-Timers, take your best shot.

73

Mike
WA4DLF


--- On Fri, 10/3/08, Carl Nord <chnord at comcast.net> wrote:

> From: Carl Nord <chnord at comcast.net>
> Subject: RE: [Hallicrafters] 40 m antenna used on 80 m - what to expect?
> To: Hallicrafters at mailman.qth.net
> Date: Friday, October 3, 2008, 11:49 AM
> In 66, as a 13 year old expectant novice I was worrying a
> lot about my
> dipole.
>  
> Nowhere could I find if the center conductor of my coax
> should go to the leg
> closest to the station, or furthest away. Laugh if you
> want. But show me
> where it says it shouldn't be hooked up a certain way!
> Clearly that was
> knowledge that others had that did not or should not need
> to be written down
>  
> One wrong connection might ruin the rig, null out the
> signal or maybe cause
> global warming. After all this was a mighty Johnson
> Adventurer that was
> going to be sending the full power of an 807 into the
> atmosphere
>  
> Carl
> WA1KPD
> Visit My Boatanchor Collection at
> <http://home.comcast.net/~chnord/wa1kpd.html>
> http://home.comcast.net/~chnord/wa1kpd.html
>   _____  
> 
> From: hallicrafters-bounces at mailman.qth.net
> [mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of
> Jim Brannigan
> Sent: Friday, October 03, 2008 8:43 AM
> To: Oliver J. Dragon; Waldo Magnuson;
> Hallicrafters at mailman.qth.net
> Cc: Waldo Magnuson
> Subject: Re: [Hallicrafters] 40 m antenna used on 80 m -
> what to expect?
>  
> Had to laugh, yes ignorance was bliss.
> I recall the novice goal was to get any wire outside, feed
> it with something
> and transmit.
> Making ANY contacts made it a good antenna!!!
>  
> I remember Harrison Radio on Greenwich St. with rows of
> Collins gear
>  
> Jim
> ?
>  
> Skip,
> 
> Sometimes ignorance is bliss. (my ignorance, in this case).
> 
> Upon receiving my Novice class ticket in 1960 I immediately
> put up a 40M
> dipole about 25' off the ground and fed 
> it with 70' or so of RG-59 directly to the pi-net
> output of my just
> completed Knight Kit 50 watt transmitter. 
> I had two 40M crystals & had a great time. The SX-99
> was connected to an 80'
> #12 copperclad longwire (the wire still 
> had the 'set' and coiled back up close to original
> shape when I took it down
> 9 years later). Didn't have to worry 
> about an antenna change-over relay - just turned down the
> RF gain on the
> SX-99 when transmitting. 
> Of course, both antennas were erected during a snowstorm -
> can you think of
> a better time?
> 
> Anyway, after about 3 weeks on the air I got the bright
> idea that 80M could
> be real fun, so I went over to 
> Harrison Radio (225 Greenwich St., in Manhattan and picked
> up two 80M xtals
> & proceeded to run the Knight straight
> into the 40M dipole on 80M. No problem. Didn't know
> what the swr was (no swr
> meter); didn't know how many of the 35 or so input
> watts
> showed up at the antenna (no wattmeter) but I worked up
> & down the east
> coast from NY; out to the midwest (Chicago, Detroit, St.
> Louis). 
> Had more fun on 80 than on 40. Less qrm andmore slow-speed
> guys to chat
> with. 
> 
> Only problem was with harmonics. My 3704kc xtal doubled to
> 7408kc and
> careless dipping one day to the harmonic
> earned me a 'special official reception report'
> from the FCC. Solved that by
> more careful tuning and a harmonic trap courtesy 
> of QST.
> 
> Bottom line - give the 40M dipole a try on 80 and you might
> be surprised.
> Have fun.
> 
> 73
> Ollie
> 
> 
> 
>  
> ______________________________________________________________


      
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