K1TTT Technical Reference
K1XX Nonsynchronous Balun
Mon, 21 Oct 1996
firstname.lastname@example.org (Fred Hopengarten)
Several people queried me as to what I meant by a K1XX Nonsynchronous
balun -- to transition between the use of 75 ohm hardline and my
It is described in the now defunct magazine Ham Radio, September 1978, p.
Here is a quick summary:
Start at your transmitter, at 50 ohms.
Next, 0.0815 wavelengths of 75 ohm coax (usually RG-11).
Next, 0.0815 wavelengths of 50 ohm coax (usually RG-213).
Next , ANY length of 75 ohm hardline.
Next , 0.0815 wavelengths of 50 ohm coax (usually RG-213).
Next, 0.0815 wavelengths of 75 ohm coax (usually RG-11).
Now your 50 ohm antenna.
Be sure to use the correct velocity factor for your RG-11 and RG-213:
solid poly = .66
Belden foam= .78
PTFE = .80
Fred Hopengarten, K1VR
Be sure to use the correct velocity factor for your RG-11 and RG-213:
Fred, minor point but solid PTFE velocity factor is .694. It is only in
the air/PTFE (tape, spline, foam, etc) that the velocity factor gets into
the region of .75 to .90. So if it isn't solid PTFE you had better check
the specs or measure the VF yourself.
John Brosnahan W0UN
Summary I: Feeding 160 Inverted-L
Thu, 17 Oct 1996 -0500
email@example.com (Lee Buller)
A lot of people are asking for summaries. So here is a summary of what is
going on. There is one I am not going to attach because is it lengthy and
be had from :
Here are the answeres I got:
Lee, your antenna should work out to a quarter wave or so. In that case,
I would try direct feed. SWR shouldn't be over 1.5:1 AND WILL DROP WITH
THE NUMBER OF RADIALS YOU PUT IN!
cut the antenna for a 1/4 wave and feed direct with 50 ohm coax. I
had mine fed 8 ft off the ground with one counterpoise radial running thru
the trees 8-10 ft off the ground and was working stuff i only dreamed of in
the past. dont worry abt matching unless you are running longer than 1/4
wave then you need supposedly a series capacitance, i found you need an l
network to match the 3/8 wave antenna. just stick with the 1/4 wave inverted
l about 135 ft or so.
I haven't used an L for several years, but when I did I followed
the suggestion of W1BB to make the wire a bit longer than 1/4 wave (140-160
feet) and use a series capacitor of a few hundred pf at the feedpoint to
tune out the reactance. You can use a variable capacitor and tune for
minimum SWR; if you like you can put the capacitor in a weatherproof box or
replace it with fixed transmitting mica capacitors.
I don't have a great score on 160 because I don't stay up all night, but
here's how I fired up an inverted L..... Used about 135 ft of wire.... fed
it in the backyard with 50 ohm coax (earth braid to the "earth sustem" - just
a 3 ft copper pipe bashed into the ground). Wire was pulled up vertically
about 30-40 ft with a halyard off the tower, and the horizontal section was
pulled across the top of the house on a rope and tied off in the front
garden. The SWR was high so I just kept trimming the wire back until I got a
match... 120+ ft gave 1.1:1. No matching network was employed at all. Now I
know that's not very scientific, and I know the experts would laugh - or
maybe cry - at this, but the antenna worked! I got VK, ZL and JA - about
the furthest DX we can work from here - all without much trouble. In fact
I've got 160m WAC hanging on the wall. I was so amazed at working VK6HD that
I sent him a 6 inch clipping off the end of the antenna!
I cannot put down any kind of reasonable earth system, although I have used
chicken fencing at the base of a 40/80 vertical in the front garden. Seems
to work fairly well, but doesn't compare with the "real" antennas on those
So, if nobody comes up with pages of formulae and all that jazz, get a pair
of wire cutters out and tune it that way. As for ATUs - there's only one
place for an ATU and that's the trash can. Match your antennas outside -
that's my philosophy and it's worked pretty well. Incidentally, my Inverted
L covered the whole of Top Band, although the SWR was a little high at the
Just to say that you can still have fun - and push out a reasonable signal -
without getting bogged down with all the arguments on the reflector about
numbers/lengths of radials, whether they should be elevated/under ground,
I've had a few L's. The one I have now is best so far. I would try
making the antenna closer to 150' or so in length and then put a capacitor in
series with the feed point to tune out the extra "length (actually inductive
reactance)" and it arrives at a feedpoint impedance of 50 Ohms. I have a 500pf
5kv fixed cap and abt 10'of RG213 (abt 20pf/ft) in parallel as my "variable".
It resonates at abt 1810 kHz (may try shortening it a bit) with a 2:1 BW of
abt 80kHz. I have abt 1500' of on-ground radials of various lengths with the
longest abt 80'. I have abt 70 countries so far, all running the TS930
barefoot (including JA and VK) from Nashville. There may be better ideas, just
A resonant inverted L will be less than 50 ohms and zero reactance.
You can increase the feedpoint impedance by making the total length
greater which will also result in a series inductance. This inductance
can be easily tuned out with a series capacitor.
It helps to have an antenna impedance analyzer like the new MFJ with
SWR and Resistance scales. You will need more radials...16 is a good
place to begin...30 to 60 is required for good efficiency...make them
straight...cut off when you can't go any further...folding wire back
Additional information will be posted from my other computer at home in
Here is what happened to me:
This was my first Inverted-L. I used #16 coppper wire from the ground to
the top of the tower where I placed a metal cross arm....jumpered over to
the tower where the horizontal element goes to a tree. Total length is
about 145 feet. I made it long for tuning reasons. I could either cut back
the wire for resonance or use a capacitor in series to tune the line at the
feed point. I opted for the capacitor. Using a pretty large variable
(about 500 pf and will handle about 5,000 watts) I was able to tune the
antenna to around 2.0 Mhz using a MFJ 207 analyzer. I did not have enough
capacitance to make the trip to 1.8 Mhz. So, I rummaged around in the hold
junk box and produced a fairly large tuning capacity made of an old
receiver. The capacitor was three sections which each section being 365 pf
for a total of around 1100 pf. Using this capacitor, I was able to tune the
antenna down to 1.8 Mhz. SWR at is 1.2 to one at 1.807 Mhz. The SWR rises
to 2.0 around 1.865 which has rather a large bandwidth for 160 in my
experience. The capacitor is 2/3 meshed, so I assume that I am using 700 to
800 pf. Before, I had shunt fed a 50 foot tower with a TH-7 and that rig
proved to be fairly narrow in bandwidth. The capacitor I am using won't
take the KW, but I have find my door knob caps in the junk box and add some
capacitance to the big variable capacitor.
The grounding system was incomplete. The ground side was an 8-foot ground
rod with not radials (worked MT and IA with the thing the first night).
Radials will be put in this weekend. All connections were done with
alligator clips and a more permanent installation will be made this weekend.
This is a cross-post from the (160 meter) or "TopBand" reflector.
Perhaps some contesters will enjoy the subject: I hope, anyway.
This is in regards to using a capacitor in series with the 50-ohm feedpoint
of a 'classic' (near 5/16-wavelength) inverted-L, which presents inductive
reactance at its feedpoint. (No need to reply--I have enough information!)
Think I'll try a length of coax as a capacitor for feeding the beast.
73, Glenn, KB1GW
From: Swanson, Glenn, KB1GW
To: 'TopBand - postings'
Subject: TopBand: Final Summary - cap for inverted-L
Date: Thursday, January 09, 1997 12:30PM
Greetings inverted-L fans,
In regards to the 'proper' capacitor to use at the feedpoint
of a 'full-length' (say, 160 to170' long) inverted-L antenna:
Thank you for, and here is, the wisdom of the reflectorites:
73, Glenn, KB1GW
My original posting:
>Okay, so I'm thinking about extending my 1/4-wavelength "inverted-L"
>out to 170 feet (+/-) and putting a (air-variable) capacitor at the
feedpoint. I know I'll need something like a 500 to 1000 pF cap.
>However, [at] what voltage rating?
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Replies received--sans names and call signs:
"Since the cap is in series with a "current" point on the antenna. HV
ratting is not as important as current ratting. a 2KV cap should be
plenty. In fact If you can build a suitable enclosure then even Air
variables work quite well. I use a 150pf air variable shunted with
several of the old surplus 100pf transmitting micas (the brown ones abt
2" square). For example to 500pf TV style doorknobs wont work because
they cant handle the current (they get warm even with 100 watts) even
though they are rated 15kvto 20kv. At 1KW the current can be on the
order of almost 6 amps (more on peaks). If you plan on using the
antenna on other bands (say with a tuner) then be careful you can end up
at "voltage" node on another band and blow the caps!I that case the
vacuum variable is more likely a better bet. I have had the best luck
finding vacuum variables at HAM fests I have paid anywhere from $35 to
$80 for them.
PS: I have two L's in this configuration--fed in phase... good luck"
"My inverted L is abt 160' long (60' vertical). I used fixed+variable
caps to achieve a reasonable match. My fixed was a 500pf 5kv old bathtub
cap and I used a section of RG213 in parallel with it as my "variable" (you
can trim the length to achieve best match). My bathtub went bad
(heated/leaked) so I was left with abt 12' of RG213 alone (abt 20+ pf/ft).
The match is now abt 1.2:1 at 1840 and rises to 2.1:1 at 1800. 2:1 SWR BW
is just under 80kHz, which seems to indicate a reasonable ground (I have
abt 1500'of many short radials) and it seems to play!! I think RG213 is
for a few KV and is a lot cheaper than an air variable. Just a thought.
73 es Happy New Year"
"Something up to about 1000 V should do the trick. This is the same sort of
cap one would use as the output cap in a linear amplifier's pi-network.
Remember: P = E*E/R. If the series resistive part of the antenna's Zant is
approx 50 ohms, then for 1500 W, E = SQRT(1500*50) = 372.8 V rms = 387 V
peak. So, a 1000-V cap should do the trick. 73"
"I'm getting ready to put up an inverted-L here, and I'm thinking of
using a length of coax for the capacitor. It would be pretty long, about
30' ( ~30pf / ft for most coaxes) but cheap and no problem with the voltage
rating (2000 - 4000v, depending on the coax type). In the ARRL Handbook,
they say you need a 1500V variable cap for the 175' inv-L. Not easy to find,
or inexpensive. 73" [See posting above. --KB1GW]
"Glenn, I have an inverted L like you are shooting for (maybe a bit longer)
I use have used some old caps with large spacing but am currently using
the old Heathkit remotely tuned cap. It has rather small spacing but doesn't
arc even at 1400 watts. I am also using an inductor so I really have an
L network. I have also used coax as a cap. I would imagine some RG-8
would work with about 5000v rating. Old 5 kv ceramics can be used as
'padders' if you can not find a large value cap. Actually, I only use about
250 pf to tune mine. Good luck and CU on topband. 73"
How about a roll of coax to tune out the reactance of the inverted L.
I have used pieces of coax to tune antennas for years. The voltage
breakdown is high and it stands up to the environment better than bread
slicers, and is a good bit cheaper. Just trim it to the required length.
I cut the braid back on the end to increase the voltage breakdown.
Then coat it Q dope and/or electrical tape. RG 8/58 is about 30 pf
per foot. You can tune up with a variable and then replace it with a
cable cut by either measuring the variable or estimating the Cap.
If you want to tune different parts of the band, consider switching in
or out different or additional pieces of coax. I had a T antenna on
80 that was tuned with a 5 ft length of RG 8 taped to the bottom end
and running back up the antenna. The shield connected to the
antenna and the center conductor connected to the coax.
Hope this has helped give you a few ideas.
Good luck on topband. 73
[See "Table 1," page 24-17 in the ARRL Antenna Book (17th edition)
for characteristics of commonly used transmission lines. --KB1GW]
-(feedline ctr conductor)->(-coax 'x' pF per ft._)_shield of coax to ant_
"Remember that adding length to the inverted L will help, but most
important is that the vertical portion be as long as possible. All you'll be
doing by adding length to the horizontal portion is making a bigger cap.
hat. Good luck"
"I've only been playing with verticals for a short while but have reading
lots of material, therefore, my suggestions are unfortunately not from
experience but theoretical.
An inverted L is really a short vertical with a capacitance hat. The hat
does two things. First, its size will dictate the reactance component at
the feedpoint. Second, it will improve antenna efficiency. By adding to
the horiz. length [of the 1/4-wavelength antenna], you'll be changing the
reactance (hence, necessitating a change in your current LC configuration)
but will slightly improve the antennas efficiency. If you can get the
vertical portion longer you'll then be improving the "low angle"
If you got the time, experiment with many options. Would love to hear
your results. I'll look for you during CQWW at months end. I currently
have a center loaded, 40 foot, vertical that seems to play OK, but it was
my first 160 vertical, so I don't have alot to compare to yet. 73"
>All you'll be doing by adding length to the horiz. portion is making a
Not completely true - by adding horizontal length *beyond a quarter-wave*,
the current maximum is moved "up" the vertical section. If the wire was
one-half wavelength long, for example, the current maximum would be at the
wire's midpoint. If the L is exactly one-quarter wavelength long, the
current point is at ground level. Raising the current maximum away from
the ground should reduce ground losses and improve low-angle radiation.
How far the current maximum should be raised depends on how long the
vertical section is. I would model the L with different horizontal
lengths and see how the pattern changes - expecting that adding length
would first improve low-angle radiation and then start to fill in the
high-angle pattern as more current begins to flow in the horizontal
section. I would also expect that there would be a fairly large range of
vertical/horizontal ratios for which the pattern changes very little. 73
Summary: Phasing 2 tribanders - coax length
Mon, 14 Oct 1996 19:18:03 -0500 (CDT)
firstname.lastname@example.org (Lynn D. Osterbur)
Here is the summary of comments regarding phasing 2 tribanders. THanks to
all you have replied. I will use a KT34XA at 103 FT and a Cushcraft A4 @
75 Ft. I did this once before with unequal (also unknown) feedlines. It is
very convient when antennas are aimed in different directions. 73 to all
Lynn; If ur going to use all three bands, use 1/4w (246/f (MHz)X VF
lines to each 3 bander.
I am thinking of phasing 2 tribanders. Approximately 28 feet vertical
>seperation. What would be the optimum spacing and length of the
Before I can comment on this, you must first tell me what the height of the
lower tribander will be with reference to ground. If you are dealing with
low tower heights (<70 feet) you will be forced to move the spacing between
the two antennas tighter, since the ground reinforcement will cause a
resulting high angle addition with the summing of the lower tribander. In
theory, and in practice, the OPTIMUM stacking of .35 wavelength boom yagis,
is about 5/8 wave seperation. If you only have a short tower, this is not
possible. If you do have the tower resources, go with 5/8 wave spacing.
>I will use a remote coax switch to select : either or both antennnas.
>I am coming up with about 28 feet of 9913 (flexible). How critical is
>this lenght other than the fact they must be equal?
Shown 32%, press for more, 'q' to quit, or 'h' for help>Comments welcome.. 73 Lynn
As far as the phasing lines are concerned, you may go with either 1/4 wave
transformers, or is you please, go with 3/4 wave transformers. Cut these
lines as close to 1/4 or 3/4 as you can, as this will affect your SWR
directly. Nextly, and just as important, make sure that any 50 ohm lines
included in the phasing lines are the same length also. It does not matter
what the length is, as long as they are both the same. You can also put the
75 ohmn transformer wherever you like in the system, provided that the 50
coax lines are connected properly, and adjusted for the same length.
The spacing of the yagis is extremely important, as it will affect
impedance, F/B ratio, and broadness of elevation angle gain maxima. This
is not easy to calculate, and is best simulated using a good yagi analying
program for your PC.
Again, all of the above specs change dramatically with yagi spacing with
regard to each other, and also with respect to ground. You also try to
increase yagi spacing, since if the spacing is too small, when you try the
lower yagi by itself, it will fall victim to the 'umbrella' effect of the
It is important to note this fact when designing the stacked system, as the
Shown 67%, press for more, 'q' to quit, or 'h' for helpupper antenna is not really affected to a great degree by the presence of
the lower antenna, but the reciprocal does not hold hold true. The F/B and
gain, and elevation angle of gain maxima is affected dramatically in the
presence of the upper antenna. You can also adjust to any desired radiation
angle HIGHER than that which you can achieve with the upper antenna alone,
by altering the phasing between the yagis. For example, by shifting the
phasing of the yagis 180 degrees, you can lift the elevation angle gain
maxima by about 18 degrees, which can be useful in close in contesting
In stacking of yagis, I would stronly reccomend reading anything by the
late Jim Lawson W2PV. Among the best of his articles - is one that appeared
in Ham Radio Magazine in November of 1980- based on stacking and stacking
design. It is worth hunting down.
Hope I was of help.
73 de Shawn
1/6 wave matching
I thought I'd post this on this reflector. It might be of some use,
especially with the 50 ohm and 75 ohm coax discussions of late.
There is a simple matching technique, useful over + - 20% in frequency,
called "one-sixth-wave matching". In this technique, two pieces of line
are inserted between the source and the load, approximately one-twelfth of
a wavelength long each. The first is at the Zo of the load, the second is
at the Zo of the source. For example, if the antenna (load) were 50 ohms,
and the transmission line to it were 75 ohms (source), we could add a
matcher consisting of a piece of 75 ohm line and a piece of 50 ohm line,
from the antenna to the main transmission line run. The lengths are
actually about 0.08 wl for 50 ohms to 75 ohms. The inverse would need to be
done at the other end to convert back to 50 ohms. This may seem like a lot
of connector pairs, but since a flexible loop is often needed at a rotator
at one end, and a flexible jumper is often used at the shack, only one
additional piece would be needed at each end. Anyway, for a single band, a
real concern about SWR, and a long run to the antenna, this might do the
GL John Matz KB9II
About Tuners and a neat simulator:
Alex wrote, in part:
> Tom. You are promulgating wrong ideas and concepts which
> will repeated by the neophyte.
Nonsense! Tom is absolutely correct!
Go to the University of Chicago web site where a tuner
simulator is set up. Read the instructions, use your
antenna system analyzer to determine the actual
R and X of the impedance at the end of the feed
line to be connected to the tuner output terminals.
Put the values into the simulator and see the result.
To do this experiment for your own tuner, you need
to know component values of the C's and L or the unit.
Or, lacking that info, use the default values for experimenting.
Simulator is here:
You will find that in just about every case, either the input
or output C value will be selected for maximum! If the
Z at the tuner output terminal is much below 50 ohms,
especially on 160, 80, and even 40, you may have to
have some extra capacity available to switch in parallel
with the output C if your output variable is only 350 pf,
or so; then will probably need another 200 or more pf.
If the Z at the "back" of the tuner of the antenna feed is
high, then note that the input C will be set to its' maximum
value. Why? That is the lowest loss, highest efficiency
set up, just as Tom has said.
I have used this simulator, once I knew the component values
within my tuner, to establish the optimum setting areas for
my operating antenna systems and band/frequencies, neat!
One tuner which used to be/is made, the XMatch is designed
with only one variable C. The other is a "bank" of parallel
fixed capacitors. These are interchanged between the input
and output positions thus, something like 500 pf, fixed is
placed at the output position for low Z loads, and the opposite
for high Z antenna feed system inputs. The designer/supplier
has this switching function patented. Why is it designed with
fixed capacitors for one set? Because that is one
good way to insure the user doesn't mess up, hi.
73, Jim KH7M