A 15 meter vertical dipole

The return of some sunspot activity got me thinking about building antennas again (one of my favorite ham radio activities). During the last couple of years of low activity I've been using an L-shaped 130 foot dipole fed about 30 feet from one end. It is only about 20 feet above ground at the feed point (the chimney of our house) and the long end runs 100 feet over to the neighbor's tower (payment for climbing it and installing his antennas).

There is a remote automatic antenna tuner (LDG AT200-PC with a second antenna connector which was begging to be used) in a weather proof box within about 5 feet of the feed point of the dipole. It has no problem getting a match on most bands 80 thru 10 meters thanks to the careful choice of feed point offset position. The station feedline and tuner control and power lines run down through the chimney into the living room fireplace (which houses a TV) and then over to a table where I have my TS-480 set up.

On a side note, the TS-480 makes a wonderful living room ham rig. Only the tiny control head and Swedish pump straight key sit on the table while the RF box is tucked inside the hi-fi cabinet. And I must mention the TS-480 has one of the best QSK implementations I have ever used.

While the low 130-foot multi-band dipole has worked well for casual contacts, I wanted to experiment with something more consistently omni-directional and with a lower radiation angle on the higher bands for a shot at some better DX during this next cycle. So I started thinking about a vertical but I really don't have any space for radials (and even if I did the WAF of radials is really really low). Reading about the GAP antennas got me to pondering construction of a full-size 15 meter vertical dipole using left over pieces of an old vertical that have been taking up space out in the garage. Some spring-like weather in the middle of February provided the final motivation I needed.

The base of the old vertical could extend to about 12 feet (with the help of a 3 foot stainless steel whip at the end) and I had an 11 foot mast pole my neighbor gave me that was only a little bit bent up. So I put the two together for my 1/2 wave dipole. I also had a coiled coax common mode choke I had used with a 17 meter delta loop during the last sun spot cycle so I recommissioned it to help balance the feed.

I did a little antenna modeling (using EZNEC demo, 4nec2, and xnec2c). I toyed around with adding some extra elements (think vertical fan dipole) in an attempt to cover 20 and 17 meters as well, but they tended to mess up the radiation pattern and were really tweaky so in the end I decided to keep it simple for this first attempt.

We have a wooden fence in the back yard with well planted 4x4 posts rising about 7 feet out of the ground. All I needed was a way to attach the bottom pole while keeping it insulated. That old nylon cutting board in the kitchen was needing replacement anyway ...

Bisecting the cutting board gave me the two mounts I needed.

Using an antenna analyzer, I adjusted the length of the top section with the assembled dipole laying horizontally only a couple of feet off the ground on a wooden table. Surprisingly, that length adjustment remained correct in the finished upright position with the feed line coming away from the antenna at a right angle.

That is the chimney over there on the right where the antenna tuner is mounted and the 130-foot dipole feed point is near the top of the mast. For the new vertical dipole I'm using a 50 foot length of RG-8 coax with the last 10 feet coiled up at the tuner. The SWR is very low over the entire 15 meter band with the tuner in bypass mode. (The analyzer was showing about 80 ohms when attached in place of the tuner.)

My first contacts during the DX contest on 2/20/2010 yielded very satisfying results. Running 60 watts I made many contacts with stations in Japan as well as contacts in Russia, New Zealand, and Brazil from here in the Seattle area.

The antenna tuner is able to obtain a match on 20, 17, and 12 meters but I have not attempted any contacts yet. I'll post again with some additional results after I have used this antenna for a while.

73 and may you have good DX this sunspot cycle.

Harry, AB7TB

Hungry cat stops computer dead in its tracks

We have an older male feline named Sir who, while large in frame, at 20 pounds is considerably overweight. This is our fault because, it being bothersome to ration food between three cats, we took the easy way out by leaving food out all the time so they wouldn't bother us. Surprisingly, our oldest cat has done just fine with this approach, but our youngest one has recently ballooned and Sir has been too heavy for years.

When we recently took Sir to the vet because his ears seemed to be bothering him, the vet suggested Sir might be allergic to the food we have been feeding him and suggested we try a special diet involving a meat he had never eaten before. This meant we had to get serious about rationing food between the three cats since we couldn't afford to feed the expensive food to all of them. And since we were rationing we decided we might as well restrict portions to something closer to normal.

Now you have to be careful about putting cats on a diet so we decided to ease them into it by feeding them "only" three times a day. After a few days they are starting to settle into a routine of morning, mid afternoon, and evening. This translates into a hungry cat standing on you in bed in the morning and staring you in the face and "hungry cat conventions" in the kitchen in the afternoon and evening. And you know how cats are when they want something from you - they start rubbing up against things and meowing.

So I'm sitting at the kitchen computer today using the computer and ignoring the cats and this just won't do. To get my attention, Sir comes over and rubs up against the front of the computer and I reach over trying to push him away so he won't accidentally press the power button. It is a typical home-brew tower machine with USB and audio connectors on the front. I'm not sure what the combination of events was but one swipe of Sir's hulking frame and static-prone fir and zap - the computer was frozen in it's tracks. That will teach me to ignore a hungry cat!

This gets me to thinking that perhaps those connections aren't properly grounded for electrostatic discharge (ESD). The front panel connector cables just go right to the motherboard and I'm sure even the grounds don't properly handle ESD. So I guess it is time to take the computer apart and see about adding some grounding straps right from the metal on the connectors to the sheet metal frame. This proved effective on another machine I had build a while back so I'll try the same cure on this one as well. Perhaps this can be the subject of a future blog including some pictures of the results.

.-.-.

Literally pounding some brass

Ham radio operators have a "contest" on new year's eve called Straight Key Night. The idea is to use archaic wireless equipment and communication methods to have a few nice long conversations, known as QSOs (amateur operators use a set of arbitrary 3-letter "Q signals" for abbreviations). If you don't have archaic radio equipment you at least must use a "straight" key (as opposed to an automatic key that makes sequential dots and dashes with a single movement of the key lever).
In addition, many contests consist of simply passing a few bits of information to prove you made a contact and move on to the next station as quickly possible but just the opposite is true of the SKN contest. The top prize for SKN is to get the most votes for "best fist" - best sounding Morse code produced by a straight key.
I haven't had the opportunity to partake of SKN for a few years but this year it was quite a pleasure. Conditions were fair on 80 meters (the 3.5 MHz shortwave band) and I managed to have 45 minute conversations with one station just a few miles away and another down in California.
The California operator was just one month younger than me and we were both licensed in 1963 - quite a coincidence! He was quite good with a straight key, if a little slow, but fortunately didn't mind me sending at 25 words per minute (quite a challenge to keep up for any length of time on a straight key). What was even better is our signals got quite strong as the 45 minute QSO progressed. It is always more fun when a signal is "pounding in" than when you have to "dig it out of the mud".
In the end my wrist got a bit sore, but it was well worth the pain. I'll have to do it again next year. Happy New Year!
.-.-.

Felines appreciating Christmas time

House cats are a funny lot given all their personality quirks. However, as they get older they all seem to have one thing in common, desire to seek out warmth. Shortly after turning on the tree lights this morning we came across this scene of Sir, our 12 year old male:


Obtaining a photo of the other end posed a bit more of a challenge but the facial expression says it all:


We have had other cats exhibiting similar behavior over the years. I can't find the photo at the moment but one classic was a cat sitting on a bunched up string of lights being tested before outdoor installation.

Another interesting behavior of the cats is their fondness for the taste of tree-stand water. It makes it hard to tell how much water the tree is still taking when the cats are drinking an unknown quantity.

.-.-.

Hungry birds posing for the camera

I've been inspired by my daughter to try my hand at blogging. This is going to cover random subjects despite the blog title. I have enjoyed playing around with digital cameras the last few years, mostly taking closeups of flowers and the like. I like to compose them to make useful wallpaper for our computers.

It has been raining a lot lately and when we got a sun break this afternoon (aka a sunny day in Seattle) the birds came to the feeders in droves. We had just replaced the platform feeder with a new plastic one (called a "dinner bell") in an attempt to foil the squirrels and I was watching the chickadees getting used to it. Hmmm... so many to chose from:


I grabbed my camera and tripod and cranked up the zoom and started snapping photos from the warmth of the kitchen. However, shooting through the double paned glass wasn't the best so I picked up and went outside for some shots of the other feeder. Of course that scared all the birds away for a while so I waited in the cold and eventually got a few decent poses from the finches.



These were taken while I was hiding low next to the patio table about 20 feet away with the camera cranked up to full 12x zoom.

.-.-. (AR in Morse which is shorthand for "end-of-message")