The Wakes I Leave...

A 42′ Portable Endfed Multiband HF Antenna with no Wire on the Ground: the “W3EDP Jr.”

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The “senior” (full-length) W3EDP, as originally described (QST March 1936, pp. 32-33), is likely the best option for a portable, HF multiband (6m – 160m), tuned antenna not requiring wires on the ground. However, it is 85 Ft. long, often too long for vertical deployment with telescopic poles and not too practical in highly constrained environments (i.e., a small balcony or a small boat). In these instances a half-sized “junior” version might prove more practical. However, the W3EDP Jr. does not seem to have received as much attention or to be as popular as its “senior” relative, which is rather surprising considering its potential characteristics:

Similar to its bigger relative, it does, however, require a tuner and a 4:1 unun.

It can be viewed as an amputated version of the better known G5RV Jr. and is the same length as the popular S9v43′, itself designed for use from 80m to 6m. In fact, when hoisted vertical the W3EDP Jr. could be consider as an S9v43′ antenna with a single juxtaposed counterpoise cable 1/5th its length (actually, it can be easily converted into a portable version of the S9v43′ by disconnecting the coax shield from its shorter branch  and connecting it instead to one or more counterpoise ground cables).

Since the full-length W3EDP can readily tune 6m – 160m, its half-size version would likely tune up to 80m. Dropping the ability to tune in 160m seems an acceptable trade-off for the advantage of having a shorter multiband end-fed antenna with no counterpoise cables on the ground.

The measures used were exactly one half of those used for the W3EDP: 8.5 Ft. of twin-lead wire with one of its wires soldered to 33.5 Ft. single wire for a total length of 42 Ft.. The materials were the same as those used in the construction of the “Flimsy W3EDP” (https://thewakesileave.wordpress.com/2016/05/22/a-flimsy-w3edp-portable-antenna-la-manquita/).

Here is an initial analysis of the antenna using the mini-VNA analyzer. The plot shows SWR (blue curve) and Z (green curve) values for the 3-30 MHz range of the HF spectrum. The W3EDP Jr. was hoisted to its full length (using the S9 telescopic mast resting on the top branches of a tree) and was being fed via a 4:1 unun.

Similar to the S9v43′, it resonnates around 5.5 MHz. The SWR for the most part is below 10:1 and the impedance remains within tunable range, being highest for 40m (as expected for an end fed 1/2 HWL wire).

Here are some data taken with the Elecraft KX3 and its internal ATU (all measurements were made in the middle of the CW portion of each band using 1 Watt and the configuration of the antenna and the connection to its twin line portion were the same for each band):

Band

SWR

No Unun
No ATU

No Unun w/ATU

w/Unun
No ATU

w/Unun
w/ATU

6m 5.8:1 1.0:1 3.1:1

1.0:1

10m 29.9:1 1.2:1 10.9:1 1.0:1
12m 9.9:1 1.0:1 7.7:1 1.0:1
15m 2.2:1 1.0:1 2.4:1 1.0:1
17m 2.0:1 1.0:1 5.5:1 1.0:1
20m 14.0:1 1.1:0 6.9:1 1.0:1
30m 8.9:1 1.0:1 2.7:1 1.0:1
40m 31.9:1 1.0:1 10.3:1 1.2:1
80m 10.4:1 1.0:1 6.9:1 1.0:1
160m 21.0:1 8.5:1 6.9:1

1.0:1

The antenna was also modeled using CocoaNEC-2:

The elevation angle in vertical configuration appears to be low with a single lobe for the low bands and increasing and becoming “hat-shaped” for the higher bands (this and the vagaries of propagation (and sprint participation) may account for the apparent predominance of relatively nearby 20m contacts in the initial trial below).

Field tests in every band will have to wait for better propagation conditions. However, initial results in 40m and 20m seem to confirm the above predictions: here are the initial CW QSOs (QRP) while operating portable during a recent SKCC WES (i.e., with realistic Rx RST reports):

CALL

Band Rx RST SPC

KK6L

40m 589

PA

K1LEE 40m 559 CT
W3DF 20m 579 MD
KA3OCS 20m 599 VA
NO8C 20m 559 OH
W4AFB 20m 589 FL
KC3DOF 20m 339 PA
K3WW 20m 559 PA
N8KR 20m 559 IN
W9DLN 20m 559 WI
F6HKA 20m 559 F

Although here it has been used in a vertical configuration, similar to the full-length W3EDP it could easily be used in other shapes and configurations,, something not readily evident for the S9v43′.

The W3EDP Jr. is being added to the backpack as another choice for a practical /QRP/P antenna, together with the Alexloop, the PAR EndFedZ’s (mono and tribander) and its “senior” relative: the 85 Ft. W3EDP.

 

Note added Aug 17 2016: Operating /QRP/P under similar conditions as above, 4 more CW contacts were made, adding two new bands to the list of QRP QSOs credited to the W3EDP Jr.: 15m and 30m:

– OH6NVC Mika, Finland (CW, 20m)
– K6RB Rob, CA (CW, 15m)
– K6DGW Skip,  NV (CW, 15m)
– DL1NKS Stefan,  Germany (CW, 30m)

 

 

 

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