Lyn,
That's a reasonable design, and if you have it high, I am not
surprised it's working out well for you. Not every ham has the liberty
to put up, grow, an antenna farm. I am in that position. I have only two
antennas up, a 20 meter vertical dipole center fed which I operate 20-10
and feed it with ladder line and an 160 meter inverted L fed at the base
with a remote tuner. I also have 5 elevated radials of varying length
connected to the remote tuner , just because. Collectively, they work
out well. It sometimes amazes me how some wire in a tree or two can be
used to reach out and touch people. :-) I have never used a beam, but I
do have a KPA500 and matching tuner which I use primarily for working
100% duty cycle digital modes. All of my contesting and DX work has been
at the 100 Watt level, except Field Day when I run QRP. So, good going
and luck.
73,
Barry
K3NDM
On 7/17/2020 9:18 PM, Lyn Norstad wrote:
Barry -
+1
I use nothing but 600 ohm OWL (True Ladder Line) and a short piece of coax
connects to a 1:1 / 4:1 hybrid balun to allow matching the impedance perfectly
with my KAT500.
The antenna is a 360' center fed EDZ (design frequency of 3.5 MHz). The KAT500
matches it on all bands 160 - 6m (on 15m, it bypasses).
The measured performance indicates excellent radiation on all bands.
73
Lyn, W0LEN
-----Original Message-----
From: elecraft-boun...@mailman.qth.net
[mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Barry LaZar
Sent: Friday, July 17, 2020 7:44 PM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] Matching resonant antennas
Wes,
You're correct that open wire/ladder line transmission lines are
not a panacea. But, in the average ham stations, open wire does overcome
high losses with high SWR, or not so high SWR. What is needed is a look
at the ARRL Antenna book for transmission line loss/100 ft. as a
function of SWR. You see that on 10 meters running 10:1 SWR the total
loss is around 1 db. And, as you go to the lower bands, losses become
less. Typical 400 Ohm ladder line has a loss of 0.2 db at 10 MHz and 0.6
db at 100 MHz. Using these data and a little interpolation, I would use
0.4 db on 10 meters and a 10:1 SWR for this to be 0.8 db of additional
loss for a total of about 1.2 db. Yes, I do use a balun and recommend
them so add another 0.5 db. Add another 0.5 db for a good tuner and we
end up with a total of 2.2 db. on 10 meters and less on 20 and it
decomposes to an academic exercise on 40 and down.
Coax on 10 starts out with a higher loss/100 feet. I will use what
I use here in K3NDM, Times LMR400. That represents 0.4 at 10 MHz. and
1.4 db at 100 MHz. That will yield about 1.2 db/100 ft on 10 meters. Add
0.25 db for a 2:1 SWR and 0.5 for tuner loss and you end up with about
1.95 at a 2:1 SWR.
Here coax wins IFF the SWR remains less than 2:1 which won't happen
over the entire commonly used portion of the band. Using ladder line
vice coax will contain losses over the entire band. This keeps things
simple and the cost should be a lot less.
As to the RCA station with a 14:1 SWR, they used no balun nor tuner
as we commonly know them today. The coupling to the final tube(s) were
balanced and was capable of making the transformation from what the tube
wanted and the reflected impedance at the transmitter end of the
transmission line. Ergo, they had a very low loss if using 10 meters
which they didn't. They typically used frequencies below 18 MHz and a
slug of power.
Vy 73,
Barry
K3NDM
On 7/17/2020 6:57 PM, Wes wrote:
I wrote about some of this in my paper ARRL Antenna Compendium paper
on ladder line 20 years ago. https://sadxa.org/n7ws/Ladder_Line.pdf
I've seen pictures of those SW transmitting plants and always assumed
that they must have been very efficient. Upon reflection---no pun
intended---now I'm not so sure. If losses mounted up, (which they
most certainly did at 14:1 SWR) they had the option of just turning up
the wick.
Furthermore, as I said in closing: "Contrary to the conventional
wisdom, ladder line is not a panacea for every transmission line
problem." In the ensuing 20 years, I've become even more convinced of
this. When tuner and balun losses are factored into this picture I
don't know why anyone would want to use this stuff. I sure don't.
I have a KAT500 and use it to tune some way-off resonant antennas (fed
with 7/8" Heliax) but I don't delude myself into thinking "I've
contained system losses."
Wes N7WS
https://www.qrz.com/db/N7WS
On 7/17/2020 2:32 PM, Barry LaZar wrote:
Resonance is over rated. The problem of believing you must have a
resonant antenna arose with the use of coax cable began. High SWRs
causes high system losses.
Prior to the widespread use of coax, open wire was used and few
antenna systems were really resonant, and nor were they reflecting a
1:1 SWR. Back then, no one cared as tubes were used and pi-net or
swinging links were used to match to whatever was connected to the
transmitter. In fact, I once visited a site that used rhombic
antennas and Sterba curtains being fed by high power transmitters.
The feed line were copper pipes about 1/4" in diameter and spaced
about 4". The SWR, I was told, was 14:1. I asked if that was a
problem of transferring energy to the system. The answer was no as
the final output stage could match it and the system losses were low
due to the type of feed line used. This was a lesson I learned 60
years ago and haven't forgotten it. The site was the RCA site the
once stood on Montauck Point on Long Island, New York.
One point that keeps getting forgotten is the conservation of energy
concept. What that means is energy can only be changed and not lost.
Typically that means transmitter energy would be changed to heat, but
not lost. What is not changed to heat on the coax will make it to the
antenna where it MUST be radiated and not lost. Yhe practical
application of this is use really good coax if you can't get to a
1:1-2:1 SWR, ot there about. Alternatively, use ladder line and a
current balun. Elecraft tuners easily tune 10:1 SWR which contains
system losses nicely. I have been doing this for a very long time and
have achieved WAS, DXCC phone, DXCC CW, and DXCC digital, and, I'm 13
short on 80 of making 5BDXCC.
73,
Barry
K3NDM
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