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--- hf:antennas [2024/01/23 18:35] – [The Loop] m0nvk
+++ hf:antennas [2024/11/04 18:29] (current) – [Good Resources] ei5iyb
@@ Line 1: / Line 1: @@
+======= Antenna Systems =======
+====== Antenna Types ======
 ===== The Simple Dipole =====
-A Simple Dipole can be created from any piece of wire you have lying around. \\
+A simple dipole can be created from any piece of wire you have lying around.
-A Dipole will normally be a half wave length for the band you are intending to work on. \\
+A dipole will normally be a half wave length for the band you are intending to work on.
+A dipole has a characteristic impedance of 73 ohms, though hams normally ignore this since it's fairly close to 50 ohms.
 Dipoles are band specific.
-{{:hf:dipole_image.gif?400|}}
+This is the wiring of a dipole at the end of a piece of coax cable. Notice the red arrow marked C.
-===== Good Resources =====
+{{:hf:dipole-feedpoint-without-choke.png?400|}}
-https://www.hamradiodx.net/beginner-hf-antennas\\
+C is undesirable unbalancing of the dipole due to the fact that the outer skin of the braid of the coax cable is not isolated from the antenna, i.e. B and C are common. To counteract this, a balun is often used. See:
-https://www.radio4all.org/how-to-build-a-dipole-antenna/
+  * https://gm3sek.com/wp-content/uploads/2019/01/G3TXQ-RC.pdf
+  * {{ :hf:gm3sek-private-life-of-coax.pdf |}}
+This animation shows current and voltage curves on a dipole.
+{{:hf:dipole_image.gif}}
+==== Good Resources ====
+https://www.hamradiodx.net/beginner-hf-antennas\\
+https://www.radio4all.org/how-to-build-a-dipole-antenna/\\
+[[https://youtu.be/v9OXRtISCjM|Dud Charman's Aerial Circus]]
 ===== The Vertical =====
 The Amateur Radio HF vertical antenna is a type of radio antenna designed for use in the high-frequency (HF) range of the radio spectrum. It typically consists of a vertical radiating element, often a vertical conductor or set of conductors, supported by a mast or other structure. HF vertical antennas are popular among amateur radio operators for transmitting and receiving signals on multiple HF bands. They offer an omnidirectional radiation pattern, making them suitable for general communication, and their vertical orientation helps in minimizing ground losses. Some variations may include additional features such as radials to improve efficiency and performance.
@@ Line 44: / Line 61: @@
 If we look at the radiation patterns of regular polygons in free space, fed either at a corner or in the center of one side, there is not a lot of practical difference among them:
-polygon	feedpoint	gain dBi	impedance
+{{:hf:loop_table.jpg?400|}}
-triangle	corner	2.79	121 ohms
-triangle	side	2.96	115 ohms
-square	corner	3.19	129 ohms
-square	side	3.30	126 ohms
-hexagon	corner	3.43	134 ohms
-hexagon	side	3.48	132 ohms
-octagon	corner	3.51	136 ohms
-octagon	side	3.54	135 ohms
@@ Line 76: / Line 85: @@
+===== The End Fed =====
+==== The End Fed Half Wave ====
+EFHW, or end-fed half wave, is generally a 49:1 or 64:1 unun with a wire cut for a specific band, often 40m or 80m (so approx. 20m or 40m of wire). When cut correctly, they can be resonant on several higher amateur bands, including the even harmonics.
+These generally benefit from a counterpoise wire, and when correctly adjusted, __do NOT__ need a tuner.
+This behaves like a dipole on the band it is cut for, but the pattern less like a dipole and compromised more the higher bands it is operated on.
+{{ :hf:endfed-unun.webp |}}
+{{ :hf:shortened-efhw-antennas.png |}}
+==== The End Fed Long Wire / Random Wire ====
+EFLW, or end-fed long wire, is generally a 9:1 unun with a "random" wire. In reality, the "random" wire needs to be cut to avoid specific lengths in order to be matchable on the ham bands.
+The idea with an EFLW is for the transformer to bring the high impedance of the end of a piece of wire down in to the matching range of a typical tuner in the ham bands, i.e. a tuner is __required__ for this antenna.
+Resources:
+  * https://sparc.asn.au/2022/04/22/random-wire-eflw-antenna-designs/
+  * https://www.earchi.org/92011endfedfiles/Endfed6_40.pdf
+  * {{ :hf:wire_lengths_for_4_and_9-1_ununs-3.pdf |}}
+  * {{ :hf:wire_lengths_for_4_and_9-1_ununs_table.pdf |}}
+Both the EFHW and EFLW can be deployed in creative ways, e.g. slopers, wound around poles, inverted L, fully horizontal, but might need some adjustment to compensate for that (and the surroundings).
+====== Matching circuitry ======
+[[https://www.onallbands.com/types-of-feed-line-chokes/|Types of feed line chokes]]