Towertalk
[Top] [All Lists]

[TowerTalk] Shortened Dipole on 160M

To: <towertalk@contesting.com>
Subject: [TowerTalk] Shortened Dipole on 160M
From: K7GCO@aol.com (K7GCO@aol.com)
Date: Wed, 19 Sep 2001 09:36:58 EDT
 In a message dated 9/19/01 4:30:17 AM Pacific Daylight Time, 
alsopb@gloryroad.net writes: << 
   What's wrong with your bridge?  Show me the math that says this is so.
    de Brian/K3KO
   
  >  I used only 1/4 wave of 90 ohm coax as that reached
  > right to the rig.  So that actually was the only coax used and a 50 ohm
   > bridge read 1:1 SWR.  K7GCO
   > >>
  Brian:  I thought I'd have to explain this even more and didn't do it 
enough.  The 1/4 wave 90 ohm stub matches 50 ohms to 160 ohms which I 
suggested adjusting the L antenna Rr to making it longer than a 1/4 wave and 
using a series Xc.  50 ohms resistive is seen at the end of the 90 ohm 1/4 
wave stub by the 50 ohm bridge regardless of the coax being 90 ohms or 
actually because of it.  The formula is Zstub= Sq Root of Z1Z2 and I'm sure 
you can do this. You show me your math now.  Now it's been many years since I 
did this and at 3 AM in the morning these are the numbers that came to mind 
typing this while listening to Art Bell and watching the History Channel out 
of the corner of my eye.  I've been on the computer for 12 hours today also.  
I did a quick calculation and a 90 ohm 1/4 wave actually will match a 162 
ohms to 50 ohms and that's close enough for RF TT work.  Some say the Zo of 
this coax is 92 ohms.  In that case that wants to see a slightly higher Z at 
the antenna and I'll let you calculate it. What do you get?
  
  In any case to take care of all the coax variables the rule of thumb is to 
vary the length of the L wire length longer than 1/4 wave and the series Xc 
value so that 50 ohms is measured by the SWR or MFJ analyzer using this 90 
ohms coax or what the hell ever it is. This concept is so simple that some 
have a problem with it.  It's a very effective way to reduce the losses at 
the feedpoint.  If you keep lengthening the antenna you will approach and 
arrive at a 1/2 wave and a couple thousand ohms which matches easily with a 
very low loss L network.  With say 3000 ohms at the tip of the 1/2 wave 
antenna running 1 KW there is about .57 Amps and about 4.5A at the other 50 
ohm end with fairly low circulating currents.  Would you believe it is so 
efficient and cool, a "RF Frost" forms on L network coil.  That's an 
absolutely true story--I just made it up.  A ground rod is all you need to 
cool the coax shield as the antenna is self resonant.  I will be running side 
by side tests of a 1/2 wave verticle over a Brown, Lewis & Epstien IRE buried 
120 radial field, over a buried 16 radial field, over 16 elevated radials and 
then just a ground rod.  And then having the base .18 WL high and 16 45 
degree sloping 1/4 wave radials and other variations such as extended radials 
on the ground like WWVH does out in Hawaii as Ted brought to light.  I've 
already done some of this but am doing it all over.  Be prepared for some 
surprises. Are there any more questions of math?  I only describe what works.

Brown, Lewis and Epstien actually ended up with 100 radials in their tests as 
optimum and had copper wire left over just enough for 120 radials so they 
just added it.  That's where the 120 came from they claimed.  I did some 
research and would you believe I found out that all 3 also had stock in 
Anaconda Copper.  Do you realize how much more copper sold with just 20 more 
radials all these years?
  
It's after 6 AM--I think I'll read the paper and go to bed.  I had a very 
good day.  I had what was potentially a $900 clutch job (145,000 miles) a 
crook mechanic tried to tell me.  After a quick phone call I fixed it in 4 
minutes and 40 seconds.  A dentist tried to tell me I had abcesses at the 
tips of 2 root canals (which are potentially very bad) that needed pulling 
and Big Bucks Bridges.  I know how to read negatives very well myself doing 
it since 1936 and got a dentist friend who didn't need work to do it over and 
he couldn't find any evidence of abcesses.  I offered him my Front Row World 
Series Tickets at Face Value as my guest. The Mariners won again and have the 
best all time won lost record.  I'm going to the game tonight.  I'd like to 
take a portable HF rig, a low 1% loss L network and load up the retractable 
roof over Safeco Field on 160 or 80M.  What a Field Day antenna!  I hope it 
doesn't trigger the circuitry that makes it move.  If you hear of a strange 
"RF Halo" over Safeco well-----it may not be a terrorist.  Someone said "when 
they heard of the air planes crashing into the twin towers they thought it 
was terrorists or a really bad control tower operator." 
 
 Since I saved so much money this week also with some other things I looked 
at some new pickups.  The Dodge Ram is Awesome.  Does anyone have any 
experience with it?  K7GCO      


List Sponsored by AN Wireless:  AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!!  http://www.anwireless.com

-----
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com


<Prev in Thread] Current Thread [Next in Thread>