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Saturday, August 25, 2012

A Choke Balun for Phased C-Poles

It is important that the baluns used in a phased verticals match, otherwise the phasing, beam pattern and gain won't be as planned. They also must handle the high common mode potential at the feedpoint. KF2YN shows two different balun designs in his April 2004 article. One is just multiple turns of coax wound around a piece of PVC pipe while the second uses a ferrite core. The ferrite core design, while more expensive, also has much less power loss. For my phased verticals I chose Brian's toroid design. It uses 19 turns of RG-174/U coax wound on a FT-240-67 core. I mounted mine in plastic electrical boxes with an eye-bolt to allow hanging from the bottom C-Pole 40" spacer. This balun does no impedance transformation. The balun coax is simply in series with the antenna feedline.

Saturday, August 18, 2012

Phased C-Pole Antennas for some Gain

How many times have we seen 18 wheelers with CB verticals mounted on their mirrors? Doing this, truckers add a little gain on 11 mtrs. With proper spacing this works even better on 20 meters.

Today was a sunny day here in SE MN. The temperature was in the low 70s and there was no sign of rain. It was a great day to meet Rodney, KD0EBT, and Steve, KD0ORM, for a little KX3 time at Rochester's Essex Park. My August 23, 2010 blog post proposing that two C-Poles be fed in phase is based on information in the ARRL Antenna Handbook. Information there states that two verticals fed in phase and spaced 5/8 wavelengths apart exhibit almost 5dB gain over a single vertical. My experiments today seem to confirm this information.

I already have one self supporting 20 mtr C-Pole antenna. I built a second 20 mtr C-Pole. This one hangs from a tree limb like W5USJ 's. A little searching around Essex Pack identified a tree with some open space to the south. I merely hung one C-Pole in that tree and set my self supporting C-Pole about 44' (5/8 wavelength on 14.1 MHz) to the south. This put the two broadside to the east/west. I fed each of the antennas with 50' lengths of LMR-400 low loss coax. At the rig I had a short coax jumper to a tee, connecting my KX3 to both antennas. I let the KX3 internal turner take care of any mismatch caused by driving the two 50 ohm C-Poles in parallel. Measurements using the Reverse Beacon Network showed that these two C-Poles fed in phase and spaced 5/8 wavelength apart really can have 5 dB gain over a single C-Pole.

Now I've another portable antenna option for those days in the park.

Sunday, August 5, 2012

CQs on a Quiet Band and KX3 Trolling Mode

Today it was great weather here in SE Minnesota for getting outside (and it was even a lazy Sunday afternoon!). Beth agreed and she also needed a little time to finish some reading before a Book Club meeting. We packed up a lunch and headed for Bear Creek Park here in Rochester.

Bear Creek Park has restrooms, picnic tables and plenty of tall (but not too tall) shade trees. While not on a hill, it is also not in a hole or valley. It works pretty well for an afternoon QRP outing. In short order Beth and I repositioned a table for shade and antenna.

When I flipped on my KX3 I was not impressed with band conditions. Across 20 mtrs I heard very few signals. I had thought I may try out KX3 / SSB by checking into the Elecraft net on 14303.5 KHz but I didn't bother trying. I moved down to around 14060, the 20 mtr QRP CW frequency, checked the frequency with a few "QRL?"s and then tried a CQ...still no luck. At this point I considered pulling out my own book and calling it a nice day for reading in the park. Chalk one up for solar cycle 24. I'm glad I reconsidered.

The KX3 does have what I call trolling mode. It can be set to send a canned message (such as a CQ), wait a programmable number on seconds, and then repeat the message. During the wait time RIT can be used to tune around for calls. The message buffer can be loaded using paddles but the easiest and most reliable method is to use the KX3 utility provided by Elecraft.

After a few minutes in KX3 trolling mode W5ESE, Scott, in Dripping Springs, TX came back to me. We had a fine QSO discussing the Flight of the Bumblebees QRP contest and central Texas. After wrapping up with Scott a short CQ netted a nice QSO with VE3/W8FIB. Tom was taking a break from fishing and running 3 watts using his K1. According to his grid square location his fishing spot is about 30 miles SW of North Bay, Ontario.

Two nice QSOs and a nice couple of hours in the park ... Don't be afraid to call CQ in a quiet band.