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Old 18-09-2015, 12:00   #31
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Re: Length of HF longwire antenna

Quote:
Originally Posted by hellosailor View Post
"I understand the whole wavelength theory, but doesn't that mean you're "tuning" the rig for a specific frequency, making it less efficient on others?"
That's the way it works. Regardless of how "specific" an antenna is, it is optimized for some frequency and that makes it less optimal for certain others. It will work best for your target, and for certain other frequencies that are multiples of that target, but still it is optimized for those frequencies.
The antenna tuner is also not the magic box they are sometimes thought of. It isn't really tuning the antenna, isn't really making the antenna better of worse. You want to make the antenna as good as you can, for the frequency(s) you need the most. Then the tuner simply makes the radio happier [sic] by providing the right impedance match to that antenna. It does NOT make the antenna any more efficient, there will still be power losses involved when the antenna has to be "matched" by the magic box. So it is still worthwhile targeting the antenna length as if you had no tuner at all, and then the system will still be optimized even with the tuner.


Also remember that despite any theories, the antenna will be interacting with the hull, mast, and rigging, so you might want to start with some cheap wire that is too long, and trim it down, to see just what the best "real world" length will be. Then replace with the good stuff.
An excellent explanation even I can understand. Thanks!
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Old 18-09-2015, 19:39   #32
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Re: Length of HF longwire antenna

Cadence,
I don't want to nit-pick Hellosailor's posting....but, I do want you to know that there is a whole lot more to it!
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Originally Posted by Cadence View Post
An excellent explanation even I can understand. Thanks!
Again, not wanting to get into the esoteric, just wanting to clarify a bit...

I wish we could go back to when we called our "tuners" antenna couplers....'cause that's what the are....they simply "couple" the transmitter/transmission line to the antenna!!
But, we're stuck with calling them "tuners", I guess...


Without delving into this deeply, for our application (mostly skywave comms, from 2-4mhz thru 22-25mhz) we ask a LOT of our antennas and couplers (tuners), and as such trying to make ONE antenna work effectively/efficiently with low-loss in the coupler, etc., is an exercise in compromise!!

As Bill (btrayfors) wrote succinctly:
Quote:
Originally Posted by btrayfors View Post
Longer is better for the lower bands/frequencies, i.e., below 10mHz. Shorter is better for the higher bands/frequencies, i.e., above 10mHz.

Several things to keep in mind about length:

1. overall length is calculated from the terminal on the tuner (i.e., includes the GTO-15 feed line);

2. electrical length is different than physical length; you must take into account the velocity factor of the antenna wire itself if you want to accurately calculate electrical length; and

3. length generally isn't critical; don't worry too much about it.

A good compromise length for all frequencies has been found to be 40-45' overall.

Bill
WA6CCA
Notice is use of the word "compromise"!!
There is a reason for this word, and a reason that I highlighted his posting earlier....'cause it explains "how-to do it", without delving into the minutia (like I do!)...


fair winds...

John
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Old 18-09-2015, 19:49   #33
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Re: Length of HF longwire antenna

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Originally Posted by continuouswave View Post
The question was rather vague, as in "how long is a longwire antenna?"



Now that's a really specific, non-vague answer.

To make a recommendation for antenna length, it will be necessary to know the intended operating frequency.
What you conveniently omitted from my post was the suggestion of a Gorden West article to look up.
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Old 18-09-2015, 19:57   #34
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Re: Length of HF longwire antenna

I could not find Gordon West's article but here is one that is even more detailed. He mentions not to make them 1/2 wave lengths. Just adding a few feet one way or another makes it work.
Maybe this article will enable continuouswave to sleep at night...This is not rocket science.

Random Wire Antennas - Best Lengths To Use For Random Wire
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Old 18-09-2015, 20:33   #35
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Re: Length of HF longwire antenna

No mention by the OP as to whether he is interested in Ham or Marine HF but it suggests to me that the interest is in marine... ' I installed the HF radio for weatherfax, email, cruising nets and occasional contact with the home-front (that last one is the least of my worries).'

If that is so then Sailmail tx would be his only concern and there are that many sailmail frequencies to choose from that the whole thing becomes a bit 'never mind'.

Using the link just posted as a guide just pick one of the following ' 29 35.5 41 feet' and measure from the tuner.

As I mentioned before ... put an SWR meter in the line... and its job done.
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Old 18-09-2015, 21:35   #36
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Re: Length of HF longwire antenna

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Originally Posted by ka4wja View Post
I wish we could go back to when we called our "tuners" antenna couplers....
Post #15

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