Did anybody take part in the 10M contest over the weekend? I wasn’t expecting to or even planning on it, but it is funny the way things work out sometimes. A friend of mine came over on Sunday with his IC-718 in tow to let me borrow for a while. My HF rig is down at the moment and he lives in an apartment and has a hard time using his. Being the good friend he is, he knew I am about to have a two week break from work and thought I would like to do some HF work over the break. He couldn’t have been more right!
I got the 718 hooked up and tuned to antenna up to 10 and started scanning. Not really expecting to hear anything, I was quite surprised by how good the signals were coming in. I made about 10 QSO’s in about the span of an hour. All of them from GA, AL, TN, and NC. I was happy. Last time I had a contact on 10M was back in July before the band just went kaput.
10M is one of my favorite bands to work. Don’t know if it is just because it was the first HF band I had access to, or if it is for some other reason. I just know I really like getting on there and making contacts. Don’t get me wrong, I have fun on the the other HF bands too, but 10M is just pure fun.
The FCC is looking to clarify the rules for vanity call signs. This from the ARRL:
On Wednesday, November 25, the FCC issued a Notice of Proposed Rule
Making (NPRM) — WT Docket No. 09-209 — seeking to amend the
Commission’s Amateur Radio Service rules to clarify certain rules
and codify existing procedures governing the vanity call sign
system, as well as revise certain rules applicable to club stations.According to the FCC, almost 80,000 licensees have replaced their
sequentially issued Amateur Radio call signs with a vanity call sign
since the program began in 1996. When the program began, the
Commission established what they called “the broad outlines” of the
vanity call sign system, concluding that call signs generally should
not be available for reassignment for two years following the death
of a licensee, or expiration or termination of the license for that
call sign. In doing so, the Commission made exceptions for former
holders of the call sign, close relatives of a deceased former
holder and club stations of which a deceased former holder was a
member.The Commission did not, however, specify all of the procedures
governing the vanity call sign system, but indicated that the
procedures “would be set out in the Public Notices announcing
’starting gates’ for the groups receiving initial priority and that
the procedures would be adjusted from gate to gate as experience
dictated.” The procedures announced in the Public Notices announcing
the gates are still in effect, but they are not set forth in the
Commission’s Rules.The NPRM states that the FCC “now believe[s] that certain provisions
should be codified in our rules, and others added, so that the
vanity call sign system will be fair, equitable and transparent to
all amateur service licensees. The Commission also decided in the
Vanity Report and Order [issued in 1996] to resume issuing new club
station licenses. We believe that certain rule changes to the club
station licensing rules may be appropriate.”
More information can be found on the ARRL website.
This is not a complete how-to on how to build a home brew dipole, but rather this article is more about the math. If you are wanting to just make a simple antenna, there is nothing simpler than a dipole. And the best part is they perform great. I personally have talked some pretty far off distances on them. For instance, from Clinton, OK to Croatia.
In the infinite universe of numbers, a few are burned into the brains of antenna buffs. The first is 492. That is the number of feet in a half wavelength at 1.0 MHz. This is a free-space half wavelength, which is related to the speed of light in a vacuum. For frequencies other than 1.0 MHz, you need to divide 492 by the frequency in MHz. Our antennas are not composed of a vacuum, but rather a wire made of metal. In the metal, the speed of light slows, and a shorter wire is required to achieve an electrical half wavelength. The classic next number used is 468. A half wavelength of wire is 468 / F(MHz) feet long. If the target frequency was 14.200 MHz, a half wavelength dipole would be 468 / 14.2 = 32.96 feet long. The dipole is fed at the center of that span.
While the 492 value is close to the truth (it’s closer to 491.7796), the 468 number can only be an approximation because the shortening amount depends upon a number of factors (it’s 5% shorter, which is a nice round number). This is why we have to trim our antennas – it’s nearly impossible to compute the exact length of a dipole due to all of those pesky factors (wire diameter, wire material, insulation, end-effect, proximity to ground or other objects, etc.).
Another number often quoted is 1005, which is used to size one wavelength loops. Divide by the frequency in MHz to find the circumference of the loop in feet. Now if a half wavelength at 1 MHz is 468 feet, shouldn’t a full wavelength be twice that amount, or 936 feet? Well, due to properties of the loop, the approximation often given for the resonant length is actually 1005.
Turns out that there is a different number often cited for inverted vees. The length of a vee needed to resonate at a certain frequency is usually a little shorter than a resonant dipole at that same frequency. One constant used is 450. Some sources will suggest that the number is 3 to 5 percent shorter than the length of the dipole.
If you use #14 stranded copper wire attached to a balun cut to the length you caluculate from the frequency you want to operate at, I think you will be pleasantly surprised with your results. I have also found out that the height of you dipole antenna makes a difference as to how far you can make contacts. Lower to the ground, I have heard stations closer to my location and been able to work them. Higher the antenna the farther off I hear and can work people. The great thing is that this is an easy antenna to setup and move around, so don’t be afraid to experiment.
If you are here and wondering what happened to the forum that OK Hams used to be, the site has made a huge change in direction. The problem of SPAMMERs attacking the forum everyday was just too much. A change was needed.
I have switched the site to a blog setup now and will make the occasional post here about ham radio news for Oklahomans. You should find postings about ham fest and contest that are coming up. Issues that are important for us as ham radio operators and hopefully some good how-to articles for things like antennas and other home built projects.
It is going to take me a few days to figure out what the site will look like and how to manage a few of the features on it. But come back and come back often. This site will be a good one to bookmark. Just give me time.
