[Top] [All Lists]

[TowerTalk] Shortened Dipole on 160M

To: <>
Subject: [TowerTalk] Shortened Dipole on 160M
From: (
Date: Wed, 19 Sep 2001 14:10:43 EDT
In a message dated 9/19/01 7:20:46 AM Pacific Daylight Time, writes:..<< 
 1.) This formula assumes a pure resistive load.  You don't have that.
 2.) Second, where does one get 90 ohm coax good for 1.5Kw?
 3.) 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
Brian: In regard to 1.) The formula does indeed assume a resistive load. So 
what?  If you adjust the length of the L antenna correctly, you will obtain 
50 ohms Rr "Resistive" (Radiation Resistance) and some R loss of the wire 
which isn't very high on 160M so I combined it with Rr--OK?  There will be an 
inductive reactance XL because the L antenna is too long.  That is canceled 
out with an equal amount of series Xc (capacitive reactance) leaving the 
Rtotal value (RF+ Rloss) at some frequency say in the middle of the band if 
you adjusted it right.  Now I assumed you knew that one has to adjust the 
series Xc at a few intervals across the band for minimum SWR.  The Rtotal 
value will vary from say 40 ohms at 3.5 MHz and rise to a value above 50 ohms 
as you operate higher in the band if you learn how to cut and try for length. 
 SWR is minimized by canceling the XL with the Xc but you don't always have 
1:1.  Any modern rig tuner will match that load fairly well at the end of the 
coax even if the variable Xc isn't varied.  I use a selsyn motor to tune the 
BC variable 3 gang Xc at the base of the L antenna.  I presume you know what 
a selsyn motor is.  One doesn't see them much anymore at the flea markets 
W7JWJ reminded me recently.  I must have them all.  I hoarded them so all 
them damn hoarders didn't get them.  I in one case here I brought the L wire 
right into the shack (no Selsyn needed--just my fingers) . I fed the wire 
right into one of my coax switches center conductor terminals after first 
being connected to the series Xc.  There was a plastic knob on the Xc shaft.  
I could just peak the receive signal also for a close match.  The 5 other 
coaxes connected to the coax switch acted like the radials for some distance 
before some of them went vertical to a beam.  I've even fed one lead of open 
wire line into the coax switch and the other lead to the coax switch case 
through a BC variable with the rotor connected there.  I do all kinds of 
tricky things that work.  Another trick is to connect the MFJ in the rigs 
receiver circuit with a coaxial switch in and switch out circuit.  This 
allows you to check the SWR of the "coax switch feed" and reduce it rotating 
the variable even without a plastic knob although it is suggested.  No signal 
is on the air to activate the normal SWR bridges that would cause QRM.  This 
is really handy in the mobile with the Screwdriver antenna changing bands.

Now if you don't understand this you will have to actually try it as I 
suggest, play with it and you will get the hang of it.  Trust me--I wouldn't 
lead you astray with something that didn't work exactly as I described.  I'd 
never hear the end of it from you and others.  

2.)  I didn't say I ran 1.5 KW as you reference.  I said "I ran 1 KW" and 
based my figures in "1 KW."  You haven't done the math I asked for.  I gave 
you the math figures you asked for.  On 160/80/40M it will handle it on CW & 
SSB.  There are different sizes of it so power is not a problem.  You can 
also drop the L Z to 100 ohms and feed it with RG 11 70 ohm coax which will 
take all you got.  I will be preparing an article on this very antenna and 
variations of it perhaps this winter if I get time.  It will answer some 
questions for some others who couldn't do the math or whatever or duplicate 
it in Eznec for some reason.

3.)The nature of the tests is for the final tuning and check out the 
performance compared to other reference antennas. As I have pointed out many 
times on TT you guys are going to have to actually try these concepts before 
challenging the validity of them.  Feel free to contact me privately 
preferably on the phone which is quicker.  No collect calls please!  Some 
have tried!  Perhaps we could actually get on the air and you would actually 
hear me for the first time.  

Now it has bothered me also that I have not even heard or worked you either 
in even more than 40 years or any of the posters.  First off you are on the 
other side of the US.  Some of my tests were run in the 30's (I don't think 
you were on then) and progressively more since until I got Eznec.  I only 
test a finished design now and then go on to something else.  I have some 
that are Butt Kickers I spend many hours on the air with and even in contests 
breaking pile ups. 

I have blocked receivers on the East coast on 10m with my 7 element 10M beam 
8 years ago, worked all kinds of DX with a variety of beams also on 20,17,15 
& 12M.  I had big signal all over the world with that beam and the feed 
system I used.  I dominated SA on 10n even during the sunspot low.  When 
Japan and Europe came in again I dominated them with 3 different beams on 10M 
and on 20m also.

This last 2 years I was on 10m just about every night about 4 PM mostly into 
Japan. I used a 3 element beam tuned for absolute max gain of 10.2 dBi wtih 8 
dB F/B, 6 ohms Z and narrow bandwidth.  I fed it with 50 ohm coax in a very 
unique way.  It worked better than it should and will duplicate on the other 
bands.  In addition to great signal reports even off the back into the East 
coast it had another unusual characteristic.  When the JA's started dropping 
down to say S6 at about 6PM, I'd still be 20/9!  A Korean would               
                      be the last station heard and I still get a 20/9 and no 
one else would call him.  I'll have it back on the air in SD for all takers 
for a comparisons--if I ever get there.  The World Series comes first and 
then maybe elk hunting with a new pickup.  I'm going to compare it to my 5 
and 7 element side by side back there.  

One of my best reports was JA3DPB I had recording of saying                   
                                                                  "Ken you 
have very strong signal-you have VOA quality -Unbelievable-you break my 
receiver."  I asked what VOA Audio meant?  He said "you are Loud and Clear 
like the Voice of America."  His 6 element 100' high helped and my 3 element 
was only 55' high.                                                            
          My log is full of reports like that from all DX and I'm not even on 
salt water.                                                                   
beam Mfg is interested in making this beam as I also came up with a simple 
way to broad band it.  More on this beam later.  It even surprises me.  

Brian If you can't hear me back there you have a serious receiver or antenna 
problem.  If you tune on a signal that gives you RF burns off your RF gain 
control and Audio burns off your Audio gain control, you will know who it is 

3 years ago in was in SD and had up an L just like we are talking about, got 
on 75m SSB, was asked to move up to a special net and worked stations all 
over the US for 5 hours straight with 600W giving them SD.  I was on 6m there 
in the spring 2 years and made hundreds of contacts giving them SD.  I used a 
2 element 6m quad 25' high running 100W.  It was fed with balanced 100 ohm 
coax into a 6M Johnson Match Box.  I could hold down 50.125 MHz for 3 hours 
straight with one contact after another.  I had great success with a 75m 
horizontally oriented quad 20' high fed with 138' of open wire line (for a 
specific reason).  I used in on 160/80/75/40M and made many contacts--even DX 
on 75&40m.  I worked Africa on 75M SSB with a 40M ground plane with a single 
radial 3' off the ground fed with open wire line feed.  That stuff works 
great when you learn how to use it.

This last 3 months I've been on a heavy project of testing 3 6M Raibeams, 
wrote an article for 73M and will have a front cover picture also I took it 
over many times with big and expensive cameras and with different cloud 
patterns behind and special filters.  I'll actually get paid for that 
material.  The 5 element 6m Raibeam absolutely Kicked Butt with 100W.  It has 
the sharpest front lobe of any HF beam I have ever used even with more 
elements on a longer boom.  It also has the best F/B/Side of any beam of high 
gain I've ever had also--at the same time.  If I didn't get them on the first 
call I didn't have the main lobe on them.  When the band was about dead I 
could still work them on the 1st call and no one else around here called them 
when I finished.  I could send you a copy of the 73 article for more details 
if you have any doubt.

For some reason I have to continually provide all kinds of proof on very 
elementary concepts to those who refuse to try what I suggest and even prove 
I'm even on the air.  I'll send you my log books if that will satisfy you.  
Many others don't have any problems and send confirmations all the time.  I 
can assure you I would be on 50 times more if I wasn't answering Emails from 
all those needing help and with trouble understanding new tricks of the 
trade.  I started at about 1 AM and composed the first Email and sent it to 
TT around 3 am.  You e-mailed back a bit later around 7 am and challenged 
what I said in a very strange way like I was promoting snake oil?  OK here is 
your answer after 11 am--the same morning.  I haven't been to bed yet and 
have too much to do to go to bed.  Now I don't know what I can do more to 
help you??  I'm still waiting for the math figures I asked for.  From now on 
I charge $50 for follow ups asking for more info when the concept described 
wasn't even tried.  If I didn't explain something enough--there is no charge. 
 k7gco wrote:
 >  In a message dated 9/19/01 4:30:17 AM Pacific Daylight Time,
 > 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 
 > 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 
 > of the corner of my eye.  I've been on the computer for 12 hours today 
 > 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 
 > 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 
 > 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 
 > by side tests of a 1/2 wave vertical over a Brown, Lewis & Epstien IRE 
 > 120 radial field, over a buried 16 radial field, over 16 elevated radials 
 > 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 
 > 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 
 > Brown, Lewis and Epstien actually ended up with 100 radials in their tests 
 > 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 
 > 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 abscesses 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 
 > he couldn't find any evidence of abscesses.  I offered him my Front Row 
 > Series Tickets at Face Value as my guest. The Mariners won again and have 
 > 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 
 > 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!!

FAQ on WWW:     
Administrative requests:

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