Wires in the Rigging: Junior and the SunCat, a Perfect Match?

As shown in the precedent article, the deployment of a wire vertical antenna from a boat, using a freestanding S9 14-foot telescopic mast, is only feasible in the absence of wind and waves. The S9 mast is heavy and friction alone will not hold its sections in position when it is continuously rocked. Rain is also a problem, as water sips inside the joints between the different sections facilitating their collapse. Hence, if the W3EDP Jr. is to be used “Portable Afloat”, an alternative method needs to be found for its deployment onboard.

The Com-Pac SunCat 17 is a unique design with some very special characteristics. It is a “gaff-rig” sailboat with a very short and hinged mast (as required for easy hoisting and also for towing on a trailer). From deck to top the mast measures 18.5 Ft.. The LOA (length over all of the boat) is about the same: 17.3 Ft., and the mast stub sits on deck 15 Ft. from the stern and 2.3 Ft. from the bow.

IMG_5517

Now, this is amazing: after all the geometry is done and the arithmetic is cleared, the two lines joining the top of the mast to the bow and the stern added together make for 41 Ft., i.e. , one foot less than the length of the W3EDP Jr.! It is as if Clark Mills had designed the SunCat 17 for the exact purpose of deploying the W3EDP Jr. as an inverted Vee…

The angle of the antenna at the top of the mast would be close to 46º. However, it is difficult to predict the effect that the proximity of the metal in the rigging (i.e., the aluminum in the spars and the steel in the standing rigging) might have on the efficiency of the antenna. One way to provide some evidence in this regard is to give it a try.

The tip of the W3EDP was attached with a nylon cord to the bow of the vessel. A small pulley was attached to the top fitting at the mast and a thin double line with a small loop was rigged along the side of the mast. The antenna wire was threaded through the loop and its mid-portion hoisted to the top of the mast. The twin line portion was left to rest on the wood of the “gallows” at the stern (i.e., the support for both the boom and the mast when trailering) and then redirected underneath it to the 4:1 unun on the aft cushion of the cockpit. (As before, the unun was connected to the Elecraft KX3 via a toroidal choke). With this arrangement some interesting QRP contacts were possible:

LZ1MS (CW, 15m, LZ1)
HI8CSS (RTTY, 20m, HI8)
AA2FM/4 (RTTY, 20m, FL)
W5ZR (CW, 20m, LA)

However, the overall impression is that although receiving may be mostly unimpaired, the W3EDP Jr. as a V on board the boat may have a reduced transmitting efficiency. This may be due to the proximity of the metal rigging or the higher take-off angle, typical of inverted “V” antennas.

The following curves show the impedance and the SWR as function of the frequency for most of the HF portion of the spectrum, as measured with the mini-VNA analyzer:

VNA_160822_175005

And here are the SWR values as determined for each band (at the center of each CW portion) read directly from the Elecraft KX3 with the ATU bypassed or after tuning:

Band (m)

w/Unun, no ATU w/Unun, w/ATU

6

4.6:1 1.4:1

10

6.6:1

1.0:1

12

6.9:1

1.0:1

15

4.0:1

1.0:1

17

5.8:1 1.0:1

20

7.7:1 1.0:1

30

2.5:1

1.0:1

40 8.9:1

1.1:1

80

5.5:1 1.0:1

160

8.9:1

1.6:1

Advertisements

One thought on “Wires in the Rigging: Junior and the SunCat, a Perfect Match?

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s