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Author Topic: random or long wire for the KX1  (Read 9333 times)
M0JHA
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Posts: 646




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« on: April 21, 2013, 06:18:42 AM »

Hello, wondering if there are any KX1 users on that use a random or long wire ? if so what lengths have you had good results with on 40/30 and 20m .Im currently using a 42 foot wire with 42 foot counterpoise and do ok but was wondering what others are using ..

thinking about a 50 foot doublet for summer but not sure how this would perform on 30m and if in fact the internal tuner would find a match , i would need around 25 foot of feeder , probably 300 ohm ..

billy
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N9AOP
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Posts: 143




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« Reply #1 on: April 21, 2013, 04:45:14 PM »

Hi,
I guess that whatever works well for you is good.  I have a K1 which I use on 20 & 40 with either a 24 foot or 52.5 foot wire with the same length of counterpoise and a 9:1 UNUN.  Last summer I had a Slovenia contact using the 24 foot wire tossed up a tree in my backyard in the Chicago area.  With the 52.5 ft wire I have near 1:1 on 20 & 40.  With the 24 foot wire I have between 1:3 and 1:5 on both bands.  Go out and have fun.
Art
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G4AON
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Posts: 529




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« Reply #2 on: April 24, 2013, 12:41:56 AM »

At my Spanish QTH I tried a "random" length of wire fed against four 1/4 wave radials mounted close to the house wall, the wire was an "inverted L" shape with the top of the vertical part about 30 foot high. The results using my four band K1 (40/30/20/15) were poor. I was able to obtain a good match, but signal reports were well below what I hoped for.

More recently I have been using a home made ground plane for 20 and 15 with good results.

If you download the Eznec demo program (http://eznec.com/), try various lengths of wire and compare the results with a dipole, doublet or ground plane... Mostly the random lengths of wire will do anything except what you hope for! The demo program will only model simple antennas, but will suffice for dipoles and ground planes.

73 Dave
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GILGSN
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Posts: 201




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« Reply #3 on: April 24, 2013, 10:42:01 AM »

I experimented with "random" wires, but finally settled on end-fed dipoles. Better efficiency, no tingly fingers when you use the wrong length!

Gil.
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AA4PB
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Posts: 12836




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« Reply #4 on: April 24, 2013, 12:03:34 PM »

Elecraft recommends for an end-fed that you stay away from any "exact" multiple of 1/2 wavelength as the very high feed impedance may be difficult for the tuner to match. I'd also recommend that you avoid odd multiples of 1/4 wavelength as the low feed impedance will cause ground loss and possibly a "hot" case on the KX1 unless you have a good ground radial system. Somewhere in between, but closer to 1/2 wave should be good. This all assumes that you have the end of the antenna connected directly to the KX1 with no feed line or other impedance matching.

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GILGSN
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« Reply #5 on: April 24, 2013, 12:40:54 PM »

Quote
Elecraft recommends for an end-fed that you stay away from any "exact" multiple of 1/2 wavelength as the very high feed impedance may be difficult for the tuner to match.

That's not about an end-fed. And end-fed has a matchbox and is a half wavelength. They meant that for a random wire I am sure...

Gil.
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AA4PB
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« Reply #6 on: April 24, 2013, 01:13:09 PM »

I never heard that before. To me an end-fed can be any length (i.e. a random length) or it can be a specific length like a 1/2 wave. It also doesn't need a built-in matchbox, it can be connected directly to the tuner as in a KX-1. Granted that a couple of mfgs make EFHW (end fed half wave) antennas with a matching device on the end, but it doesn't have to be that way to qualify as an end-fed antenna.
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GILGSN
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« Reply #7 on: April 24, 2013, 02:02:50 PM »

I understand what you mean.. Yes, you can call a simple wire an end-fed. However, it is common to call an end-fed a half-wave wire with a matchbox. That's what I meant. In which case a half wave wire is better.. A simple wire is most commonly called a random wire, and used with a counterpoise, in which case a half-wave wire is to be avoided..

Gil.
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AA4PB
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« Reply #8 on: April 24, 2013, 02:41:03 PM »

I guess I'm too old to keep up with the new language  Grin  In the past any wire that was fed from the end was an "end-fed". It could be a random length (whatever fit between the supports) or it could be a specific length like 1/2 wave, 1/4 wave, or any other length that was not random.

At any rate, what Elecraft was talking about was a wire antenna of some length that was connected directly to the KX1's internal tuner.

By the way, doesn't a "dipole" mean two poles. It seems to me that it can't be a dipole if the feed point is at one end.

« Last Edit: April 24, 2013, 02:44:39 PM by AA4PB » Logged
GILGSN
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Posts: 201




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« Reply #9 on: April 24, 2013, 03:52:16 PM »

Could be my interpretation too. I haven't been a Ham for that long...

Quote
By the way, doesn't a "dipole" mean two poles. It seems to me that it can't be a dipole if the feed point is at one end.

LOL, another one! Maybe the two poles can be connected as a single wire!?

Gil.
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M0JHA
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Posts: 646




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« Reply #10 on: April 25, 2013, 10:52:27 AM »

Thanks for the replies chaps ..  the wire i use at the moment is a 42 foot end fed with a 42 foot counterpoise lay on the ground , it's mediocre on 40m great on 30m and deaf as a post on 20m  Grin  I thought it would have trouble matching on 30 as the length is near 1/2 wave .. 

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WB6BYU
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« Reply #11 on: April 25, 2013, 11:50:14 AM »

An "end-fed" is any antenna fed at one end.

An "end-fed half wave" is a half wave antenna fed at one end, with any of a number
of impedance matching methods, including Zepp fed, a dedicated tuner, or connecting
it directly to the plate of the output tube.

A half wave antenna has the same radiation pattern whether it is fed in the center
("dipole"), off center ("OCFD"), or at one end.  So from a practical point of view, when
comparing radiation, you can refer to them all as dipoles if you wish in discussions
where the feed method isn't important to the topic.  Many antenna text books, for
example, will assume the current pattern on a half wave dipole without any mention
of the feed method used to generate it.

A "random wire" is just that - of random length, either whatever fits between two
supports, or however much wire happened to be left on the spool.  A 43' wire, for
example, is not truly a "random wire" if you specifically cut it to that length, though
because the electrical length varies from band to band it could be considered one
when used on multiple bands, the point being that the feedpoint impedance and
radiation pattern can vary significantly.


What lengths work best will depend on the bands you want to cover, how the
wire is installed, and the matching capabilities of your tuner.

A strictly vertical wire will work best when the length is 5/8 wave or less, as it will
develop high angle lobes when longer than that.  But while the common 43' length
is 5/8w wave around 20m, signals are not more than 1dB worse on 15m and 10m
than they would be with a shorter wire, so it may be a reasonable compromise length
if you also want to work 40m and 80m.

The situation is different when the wire slopes (at least in the direction of the
slope) and it is possible to get some bidirectional gain by choosing a good combination
of wire length and slope angle for the desired bands.

Whether a vertically polarized wire will be better than a horizontal dipole will
depend on the height of the latter and the ground characteristics:  a vertical
is usually better for DX when it is over salt water or marsh, while a dipole may
be better in other circumstances (especially when the ground slopes down in
the desired direction.)

So the wire length will depend on your operating preferences as well.

And generally a single-length counterpoise is NOT the best solution:  several
shorter ones are better if they are on the ground, or a quarter wave wire
for each band if elevated.
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KB2FCV
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« Reply #12 on: April 29, 2013, 10:42:12 AM »

I use the antenna suggested in the Elecraft manual of the auto antenna tuner for the KX1. I think the radiating element is about 28ft (I had tried 24 feet but it didn't want to load that well). I forget how long the counterpoise is, but it's in the manual. For a lightweight "trail friendly" antenna I can carry in a ziplock bag.. I think the antenna works well for what it is. I've worked into europe with this antenna. It loads up on 40, 30 and 20m.
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K3VV
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Posts: 13




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« Reply #13 on: April 29, 2013, 02:51:47 PM »

As others have said, it's a matter of avoiding lengths that are multiples of 0.5 lambda on bands of interest.

Here's an article that shows suitable lengths for multiband end-fed wires

http://udel.edu/~mm/ham/randomWire/

And another with slightly different numbers:

http://www.hamuniverse.com/randomwireantennalengths.html

The following lengths in feet satisfy the constraint on all US HF bands including WARC bands:

29  35.5  41  58  71  84  107  119  148  203  347  407  423

I use 35- and 85-foot end-feds on hikes with my K1/KAT1.  The 85-foot antenna (called a W3EDP when used with a 17/6.5 ft counterpoise) tunes and works pretty well on 40/30/20/17 m if you can get it high enough. 

And of course you need one or more counterpoises as others have said.


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KB4QAA
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« Reply #14 on: May 03, 2013, 03:42:42 PM »

The KX1 manual gives example antenna+counterpoise lengths for each band, that will work with the optional internal tuner.

These are absolute minimal antennas for getting on the air.  They will perform much better, and match more easily by adding additional counterpoises, e.g. 1,2,3 more fanned out under the antenna.  Adding counterpoises/radials is the simplest way to improve single wire/random wire operations.

Any tuned, antenna resonant on a given band will outperform these simple wires.

The key to more flexible operations is getting an external tuner that can handle a wider range of impedances and different feedlines, i.e. coax and balanced line.

The key to light weight antennas is using small wire like Wireman 26AWG copper clad steel flex wire, and light feed lines like 300 ohm TV twinlead, or RG174 (short length) or some flavor of open wire line.

"There ain't no such thing as a free lunch". 
You won't get fabulous operations from a KX1 and just any scrap of wire you found laying around.  Add a quality antenna and some better matching box and QRP really starts to sparkle!   bill
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