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[AE9MM]

I intend to erect an end-fed long wire antenna between two trees and want to be able to operate on 10-80 meters. If I employ a very good antenna tuner and my wire is at least 100 feet long, will I have any problems? If so, would incorporating a loading coil on the antenna offer any improvement? My feed line will be 400 Max coax and the run from the antenna to the shack will be about 40 feet.

[KI5FJ]

Peter, Any HF antenna that is close to the shack will produce RFI in the shack. Your 40 Ft of coax implies a close-in antenna. You did not mention the wire shape and height. Will the antenna be working against a counterpoise ? Impedance matching will require a robust manual ATU. Be Safe especially near power lines! 73 Joe O, K I 5 F J, NNNN

[AC9ZL]

Some wire lengths will be harder to feed on all bands 80 through 10 meters. See https://udel.edu/~mm/ham/randomWire/ for details.

I use an 84' long end fed and a 17' long counterpoise connected to an MFJ-941D tuner for FT-8 contacts on 80, 40, 30, 20, 17, 15, 12, and 10 meters. My computer which is connected to my transceiver was unhappy about the RF, so I purchased 2 packages of 10pcs 5mm Clip-on Ferrite Ring Core Bead Choke RFI EMI Noise Filter Cable Clip from ebay, put them on the computer USB cables, and now have no computer issues while operating. Actually the problem went away once I installed the first package, but since the second package was already paid for, I installed them also.

I believe that a beam on a tall tower would be better than my long wire antenna installed between the top of the house and an old flag pole in the yard. But for now, this antenna is allowing me to make contacts around the world.

[W1VT]

That type of antenna is hard to predict because of the interaction between the feeder and the antenna.
But, hams often have the luxury of  designing stuff via trial and error.

Put it up, measure the SWR at the antenna tuner, and use one of the many  feedline calculators to determine how much power is lost in the feedline.
Some calculators, such as the ARRL Antenna Book's TLW, will also estimate the tuner loss.
The loss can be excessive if the SWR is high on the 400 Max coax, though not as bad as if you were using 8X or 58.

If you are running a barefoot 100W radio, I would suggest using the popular 80 through 10M  EFHW antenna with a matching transformer.
A lot of folks have had good results with them.  They do have a moderate amount of loss, perhaps 1 dB or 20%,
but that may be a good compromise compared to having to design your own system via trial and error.

[N8NK]

You might want to consider going with an 80m end fed with Milti-Tap UNUN rather than the random length wire you mention.
Using my homebrew 8 (or 9) tap multi-tap UNUNs, I rarely have to use any kind of tuner, whether external to the rig or internal. My laptop sits right next to my rig and has never experienced a hitch. I only run 100 watts. I've never experienced 'RF on my audio' when running phone.
The antenna cost about $20 to build.
The versatility of a multi-tap UNUN is beyond belief in my opinion.. and I would like to share with you what I've done with one. I have a YouTube channel but it's not monetized, and I do not provide any kind of link that generates income. I'm a retired ham of 48+ years and it's fun sharing what I do.
Here's a playlist for my end fed multi-tap UNUN 'work':
https://www.youtube.com/playlist?list=PL3CPduOS04Ncrid9dWw-p5fWFQkvMLKIi
Good luck and have fun! Summer is almost here
Chuck, N8NK
dit dit

[AA4PB]

Feeding an end-fed long wire with coax cable is going to have huge amounts of loss on some bands due to the very high SWR. The tuner may be able to match the impedance to the 50 ohm radio but it won't do anything about the loss in the mismatched coax feed line. As a worst case scenario, suppose the long wire is a multiple of 1/2 wavelength on the band you are operating. The antenna feed impedance may be 2000 ohms but the coax is 50 ohms. The swr on the coax will be 40:1 and the loss will be quite high.

I use an inverted-L antenna that is about 50 feet vertical and 150 feet horizontal. I have an SGC-230 tuner mounted at ground level out at the feed point. Buried radials connect to the tuner ground terminal and the antenna connects directly to the tuner. The long coax run (120 feet) to the radio operates at low SWR and has minimum loss on all bands (160M thru 10M).

[W1VT]

That autotuner setup is a nice option for a 100W radio if you don't mind the work involved in running radials.

[WB6BYU]

I intend to erect an end-fed long wire antenna between two trees and want to be able to operate on 10-80 meters. If I employ a very good antenna tuner and my wire is at least 100 feet long, will I have any problems?

That should be an effective length for 80-10m.
It can be matched at the feedpoint using a simple
L-network antenna tuner with one coil and one
capacitor.

If so, would incorporating a loading coil on the antenna offer any improvement?

Probably not.  A loading coil helps when an
antenna is less than 1/4 wavelength long,
but your proposed length is longer than that
on all specified bands.

My feed line will be 400 Max coax and the run from the antenna to the shack will be about 40 feet.

Now we get into the details, which can make
a big difference...

First, coax is similar to a lamp cord:  if you
only connect one of the two wires, it doesn’t
work.  You really want something connected
to the coax shield at the feedpoint - a ground
stake, ground radials, “counterpoise”, or
some other place for the other side of the
RF to flow.

Now, coax is different in that it effectively
has 3 wires:  the center conductor, the inside
of the shield, and the outside of the shield.
Without an explicit connection, RF will flow back
down the outside of the coax and into the
shack, so effectively the coax itself acts a
radiating part of the antenna.  That’s really no
different from just extending the antenna wire
into the shack.

The next issue is the impedance that the
tuner has to match.  At the feedpoint, the
impedance for that length wire will be
above 50 ohms on those bands, so a simple
tuner will work fine.  But the impedance
gets transformed by the coax:  on 20m,
with 40’ of LMR-400, if the antenna
impedance is 500 ohms, the tuner will
have to match 8 ohms instead, which is
going to require a different tuner
configuration, and like higher losses in
the tuner due to the low resistance.

Then there is the issue of losses in the
coax cable.  That depends on the antenna
impedance and the type and length of coax.
In the above case, the loss is about 17%,
which isn’t bad.  If the antenna was 5000
ohms instead, you might lose over half
your power in 40’ of coax.  That might
still be acceptable to you in some cases,
where convenience is more important
than performance. 


The best approach (from an engineering
perspective) generally is to use a remote
tuner at the feedpoint, so the coax operates
at low SWR.  Personally, I’ve had good
results just bringing the end of the wire
into the shack and using a manual tuner.
Others use a 4 : 1 UNUN at the feedpoint,
which may reduce losses on worst case
bands (while sometimes increasing them
somewhat on other bands).


So while the wire itself is capable of good
performance, a lot will depend on the
details of how you feed it.

[K1KIM]

I have a 127' wire for 80-10M in addition my other antennas. The feed line is approx 175' of coax into a common mode choke and then a 49:1 UNUN. By necessity the feedline is 135' of 400 and 40' of 8x.

My SWR  is acceptable with the wire being approx 2600 ohms before the transformer. It's 52 ohms after.

The difference with a counterpoise is negligible.

[W9WQA]

first,,,try something.  you learn all by yourself