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Author Topic: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.  (Read 1644 times)

gil

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Great read... File attached.

Gil.


caulktel

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #1 on: August 18, 2017, 12:28:03 PM »
It is a good read. I've never thought of a guitar string as a antenna, but it was good for understanding it.

Joel
N6ALT

SlowBro

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #2 on: August 24, 2017, 07:54:31 AM »
Looks like a good article!

I had not given an end fed much thought until you recommended it Gil and now I am convinced that's what I want to carry in my pack. Reason being, I don't need any heavy coax at all. I'm building a small rig in a plastic box and will just put the antenna mount directly on the PCB.

I see the recommendation is for a 22 gauge radial. I'm going to try to get away with a thinner radial by using fishing line and taping the wire to that, relying upon the fishing line to bear the weight. (The combined weight may be heavier than 22 gauge, I don't know. But it is cheaper since I have all that I need on hand.) And will segment the radial for different bandwidths, connecting and disconnecting as needed. I bought some bullet connectors but I later found that inline banana power plugs used for RC car batteries may be a better approach.

Good stuff.
« Last Edit: August 24, 2017, 08:10:17 AM by SlowBro »

SlowBro

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #3 on: August 24, 2017, 08:18:22 AM »
Does the variable capacitor need to be 250pF or could a 50pF varicap be used with 200pF additional fixed caps in parallel? I realize this reduces the tuning range but I only care about the lower portion of 40m.

Another question, what is the minimum height in wavelengths the antenna end needs to be off the ground if doing an inverted L, sloper, or inverted vee, like these? I've not found any recommendations anywhere.
« Last Edit: August 24, 2017, 08:53:58 AM by SlowBro »

swxx

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #4 on: August 24, 2017, 10:13:38 AM »
Here is some videos that may be interesting regarding pseudo-half wave end fed working on 5 amateur radio bands 40/30/20/17/15m, with tuner, but seems quite simple, effective and efficient:

https://www.youtube.com/watch?v=VXo0XucRpt0

https://www.youtube.com/watch?v=zGkC321Cwl8

Looks like a really simple and good antenna to have along with any others, for portable use.

swxx

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #5 on: August 25, 2017, 09:11:07 AM »
And here a great video by Gil on the EFHW tuner kit: https://www.youtube.com/watch?v=yRedmR9urE4

cockpitbob

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #6 on: August 25, 2017, 09:25:13 AM »
Does the variable capacitor need to be 250pF or could a 50pF varicap be used with 200pF additional fixed caps in parallel? I realize this reduces the tuning range but I only care about the lower portion of 40m.

Another question, what is the minimum height in wavelengths the antenna end needs to be off the ground if doing an inverted L, sloper, or inverted vee, like these? I've not found any recommendations anywhere.
For the cap, yes you can mix variable and fixed capacitors.  Make sure the fixed capacitor is a fairly high voltage (100V or more) cap.  A mica cap would be best, but a good quality ceramic with NPO/COG dielectric (preferred) or X7R (less temperature stable but still OK) dielectric will be fine.

For the wire, don't stress over it too much.  Outside my window I have 63' of insulated 22AWG wire slanting up to a tree.  It's just plain old stranded copper hook-up wire and it's been there for 4 years and hasn't broken yet.  The Wire Man's steel core stuff (https://thewireman.com/antennap.html)  is great, but I'm having trouble wearing out my several 22AWG copper wire antennas so don't see a need to upgrade.

SlowBro

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #7 on: August 26, 2017, 02:43:03 PM »
Ok thanks and what is the recommended minimum height in wavelengths the antenna end should to be off the ground if doing an inverted L, sloper, or inverted vee?

cockpitbob

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #8 on: August 26, 2017, 04:15:28 PM »
Ok thanks and what is the recommended minimum height in wavelengths the antenna end should to be off the ground if doing an inverted L, sloper, or inverted vee?
That's always a good topic for conversation.  Hopefully someone here will post a link to a nice summary of different wire antenna configurations and their patterns.  A full answer would fill a text book, but here's my general rules of thumbs.

Lower to the ground = higher takeoff angles.  Within 1/4 wavelength of the ground or less gives good NVIS patterns.  Higher up gives low takeoffs for Dx.  This page shows some nice example radiation patterns for a dipole at various heights.  http://www.hamuniverse.com/wb4yjtdipolepatterns.html

Vertical antennas give low takeoff angles for good Dx.  Bad for NVIS regional comms.

Inverted-V antennas are also good for Dx with low takeoff angles even when fairly low to the ground.

Inverted-L with good ground radials is similar to a vertical, but with slightly higher takeoff angles.  They are strangely omnidirectional. 

End fed antennas are particularly hard to accurately model, especially if they aren't half-wave resonant but being forced to look like 50ohms with a tuner.  If the wire is truely 1/2 wave long, you can treat it like a normal dipole.  It should work about the same.  When I use my 63' piece of wire at 21MHz it is 1.5waves long and I have no idea what it's going to do in an inverted-V configuration :o .

Frankly, I don't worry about it too much.  For portable operations, if I'm trying for Dx I'll try to get the antenna vertical (I've gotten a line over trees 70' tall with my slingshot and fishing reel 8) ).  Or maybe drape it over a high branch for an inverted-V.  Sometimes I'm lazy and string it horizontally over branches just 10-20' up.  Whatever I do, I usually make contacts and have fun.
« Last Edit: August 26, 2017, 04:21:14 PM by cockpitbob »

SlowBro

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Re: Understanding Your Multiband End-Fed Half-Wave By Daniel Marks, KW4TI.
« Reply #9 on: August 27, 2017, 07:48:38 AM »
Ok that makes sense. It should work about the same as equivalent center-fed designs. I like the flexibility of the end fed and especially not having to carry coax.