Thursday, January 31, 2013

Ham Life: The Struggle

Well now, seems like we had ourselves a little storm or something last night.
I knew this had happened:

Fallen is the Dipole!

Fallen is the W3EDP!

because I'd seen it on the ground the day before. There was a mighty wind a'blowin'. What I didn't know was that the W3EDP had lost a support too.

Woe is me! I got to thinking about the situation. My reason for going ahead with the stubbed antenna project was because the dipole had fallen. No better time than the present to go ahead and make something better. First things first though, I needed to secure the W3EDP in a position where if it's going to be up at all, I want it to be usable.

I broke some rules about how you are supposed to orient ladder line:

Yep, it's Bent!
 It's all good though, pragmatism trumps theory all the time.
Right now the W3EDP is deployed to a single support. It does not touch the tree the support wire drapes across, and is in free space as an inverted-vee. I checked it to see if it got noise, and sure enough, it's noise on 40m, and tunes up nicely. Tonight I may try to get "The Killer Watt Radio" on the air, and see if it can't snag me some tasty DX.

After doing my "radio check" I decided to roll up the 40m dipole. I need to work on it some, the whole thing is over ten years old, and it's beginning to look a little worn. I plan on using the spot it was in to deploy the new antenna I introduced yesterday. Don't tell anybody, but I'm also thinking about putting up a dipole for 80m, and fed with ladder line. The W3EDP will tune 80, but I have a plan for getting another antenna up high, like about 50' high.

What does ten years do to an antenna?
A bit Crufty She Is
Makes the outside go from copper red to dirt brown/black.
Funny thing is that when this antler was in the church attic, it didn't get too bad over the couple of years it was there. It spent a lot of time in storage, and was sitll a lil shiny when I deployed it in the yard the first time. Now it has almost a film on it. Strange. I'm thinking I should replace the wire at a minimum. The wire is about coming out of the ears where it attaches to the balun too. Not too bad I don't think. The UHF Connector still shines good. Must be something to using Coax seal and electrical tape over the connection...

Now tonight, if I'm still awake when I get home, I'll get the Decoupling Stub Antenna on the workbench!
If you have a copy of "More Wire Antenna Classics Vol2" by the ARRL, it's Chapter 3, page 17 should you want to follow along.

Ok, Last nite I got the first phase of the antenna built. I attached a center insulator to two 8 foot pieces of ladderline. Then I realized I was doing it wrong! LOL!
Pics during testing phase to follow...

Wednesday, January 30, 2013

Antenna Modeling and Making

I've literally been working on this post for a while, just haven't had the time research what needed to be researched. Still not done researching either ;-) This is what I would call a first effort.
After reading the latest antenna-centric issue of QST(way back in March 2012), I was a little disappointed. I knew I would be when I saw the front page and read "Special Ad Section Inside!"
I was hoping to read more about actual antennas. That is not to say that what articles there are not excellent, they are well worth reading. I guess I just can't get enough reading in on antennas. I'm always looking for a good idea or three. After looking through the magazine, I decided to work on modelling a multiband antenna project from the book I received when I rejoined the ARRL.
The idea is simple, you use shorted quarter wave stubs off the end of the antenna to isolate resonant sections. That's easy enough to understand, right? Ok, so I needed to see this antenna, and think about it for a second, and then I got it.
Multibands without tuners!
   This is a big win for me, anytime I get to avoid a tuner is a good time.
Relatively simple to build!
    450 ohm Feedline, antenna wire, solder, insulators, and measuring tape. No traps to wind, no coils to dip, no ultragreezy uber kul big dollar capacitors either. Just wire, lead, tin, plastic.
Mostly full size on lowest operating band.
    OK by me, I've got room for a 40m Dipole in the back yard.
Needs three supports.
   Could be a big deal to get all straightened out.

The model:
Click on the link, and copy and paste the NEC file into a text file, save the text file as a .nec.
I'm pretty sure I'm doing it the wrong way :)
The internets so far have been no help, they simply don't know how to model this.
The build:
I will build this antenna in stages, testing each stage as I complete it, the object being a permantly install, no tuner triband antenna on 10, 20, and 40m.

Tonight begins the build. First Up, 10m Section.

Tuesday, January 29, 2013

Short Note on RF Absorption and Coil Forms

Recently, on the "Glowbugs" google group, there was a discussion about whether a pill or vitamin bottle was suitable for use as a coil form for a tank curcuit, or other more general RF use (loading coil form, etc).
According to that fine bunch of OMs and YLs, the test is temperature after being microwaved for a bit. Here's how the test works:
1. Take a microwave safe dish, and put a cup of water in it. Make sure dish is shaped so that both dish and test bottle can fit in the microwave oven without one being on top of the other.
2. Clean and dry the container you want to test. I tested a bottle that held fiber, that's what's in the picture. Trickiest thing about the prep work on this baby is that you want to make sure all the metal from the freshness seal is removed from the rim.
3. Place both the test bottle and the cup of water in the microwave. Take note of the temperature of each, "room temperature" is as precise as this measurement needs to be.
4. Nuke it for a minute. (see below for further advice)
5. Compare temperatures: the test bottle should still be at room temperature, and the water should be noticably hotter (scalding hot on some microwaves, so be aware!)

Them what was tested.
Above is my test bottle, a repurposed fiber containment vessel. Errr, it's not mine man... I'm to young to take a fiber supplement! (maybe...)

K5KVH had mentioned the RF microwave test, and this is what hed had to say way back in 2011 on the Glowbugs list:

PVC is easy to verify if it has additives to increase loss. You can

check your PVC easily with the microwave test. Put a sample of the pvc
on a paper towel in the microwave oven. Put a cup of water in there
next to it. (no metal trim on cup, plain china).

Set the microwave to 3 or 4 minutes. When you see the water is boiling,
stop the oven. Carefully test the pvc with a wet finger tip, to see if
it got warm, ie warmer than the hot air around the cup.

If not, it is good for HF for sure. This is based on a formula for
dielectric loss that shows such loss is directly proportional to
frequency, the higher the test frequency, the higher the loss would be
for a given material. Thus, no heating at microwaves means it is
a good insulator at HF.

Ok, I will buy that.
My test results indicate that this material is good for winding tank circuits, or whatever, at HF frequencies.
It is made of "Recycle Material Number 2", ie High Density Polyethylene (HDPE).
I recently acquired some more tubes, so I'm probably going to be using this soon.
I also have pillbottles.