[Elecraft] End fed antenna - length and SWR

Tue Oct 8 23:15:20 EDT 2013

AAArgh Dave. Mia culpa. 66 feet is a half wave on 40, so you are good. It's
on 80 that a counterpoise/ground starts to become important. 

The basic point is that end fed antennas shorter than 1/2 wave become more
and more dependent upon a good ground system for good efficiency. 

73, Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Ron D'Eau Claire
Sent: Tuesday, October 08, 2013 7:59 PM
To: 'Esquer Dave'; elecraft at mailman.qth.net
Subject: Re: [Elecraft] End fed antenna - length and SWR

Hi Dave:

You don't mention a ground/counterpoise. With a 66-foot radiator, that
becomes important on 40 and substantially more so on 80. 

One 40, the impedance at the end of a 66 foot radiator is very, very high so
very little current flows into the antenna. That's good because that means
very little current needs to flow in to the RF ground/counterpoise --
whatever it is. The less current, the less a poor ground/counterpoise will
impact the performance. The same is true on the higher bands because, even
though the impedance a the end of the radiator changes, it is never anywhere
near as low as it is on 40 or 80 meters. 

The other issue is the feed line. Presumably you have coax between the rig
and the unun. The higher the SWR on the feed line, the greater the losses.
The SWR at the rig end only tells a little. It's the SWR at the antenna end
that matters. If it's accessible, I recommend checking it there and then
consult the coaxial cable loss tables available in any Antenna handbook or
on the internet to see what it is. 

As for the analyzer, they are nice. I've used the in commercial work, but
after 60 years of stringing up wires and building beams etc., I've yet to
find one important in my Hamshack. They are good for helping to figure out
what's wrong when you design an antenna and the SWR is off of the chart
unexpectedly. In  that situation they can speed up figuring out what went
wrong much faster than trial and error adjustments with an SWR bridge.

Welcome to a great Hobby. You won't be a 'newbie' for long, Hi!  

73, Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Esquer Dave
Sent: Tuesday, October 08, 2013 6:40 PM
To: elecraft at mailman.qth.net
Subject: [Elecraft] End fed antenna - length and SWR

Hi folks, 

Newbie HF Dave here again with an end fed antenna design question.

I have an EARCH (Emergency Amateur Radio Club, Hawaii) end fed 6-40 meter
multiband HF antenna. Part of the design is the 9:1 UNUN (unbalanced to
unbalanced) toroid matching transformer. I have replaced the 30' wire with
66.5 feet of 18AWG Wireman silky 532. My end fed is in a horizontal (slight
slope) orientation, east-west. The antenna is about 50' above the ground (I
have a 3 story house and pine trees close by).

I do not have an external antenna analyzer, yet.

Using the ATU in my KX-3, I have the UNTUNED SRW values below. With the KX-3
ATU, the KX-3 DOES tune all of these bands with no problem.

Question: Should I do anything to improve QRP performance, shorten/lengthen
the wire, or should I just go with the flow, hang loose and not worry and
just enjoy my rig?

REMEMBER, newbie Dave, be gentle. I've been tracking the long wire
discussions on the list, there is lots of fervor.

[My key = frequency/SWR]

80m
3.50/2.0
3.752.9
4.0/3.7

40m
7.0/6.9
7.15/6.9
7.3/6.9

20m
14.070/2.9
14.2/2.8
14.35/2.7

15m
21.0/2.8
21.45/3.0

10m
28.0/2.2
29.0/1.8
29.7/2.5

6m
50.0/3.0
52.0/2.3
54.0/3.7

Thanks in advance,
Dave

More static, more of the time .

Dave Esquer, K6WDE
dave.esquer at gmail.com
http://www.daveesquer.com

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