[TowerTalk] Shortened Dipole on 160M

alsopb alsopb@gloryroad.net
Wed, 19 Sep 2001 14:20:11 +0000

This formula assumes a pure resistive load.  You don't have that.

Second, where does one get 90 ohm coax good for 1.5Kw?

Third, it has always bothered me that you are not in my log after 40
years!  I am extremely active. Do you actually test anything on the
air?  What is the nature of these tests?  Many of the other prominent
posters here are in the log many times.

73 de Brian/K3KO

K7GCO@aol.com wrote:
>  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

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