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Here is a spreadsheet I designed in Microsoft Excel for calculating the first cut and the final cut (after testing) of a 1/2 wave dipole, whether center-fed, classic off-center-fed, Windom, or New Carolina Windom. If you use it for a plain ol’ center-fed dipole, just ignore the references to “long leg” and “short leg” — the numbers will still be right. Anyhow, you’re welcome to use it, pass it around, whatever:

DipoleWorksheet.xls (Microsoft Excel)

I’d enjoy hearing from any of you who end up using this spreadsheet to build an antenna!

If you find any bugs in this spreadsheet, please let me know. Note that it is protected for your convenience, but you can unprotect it anytime you like to see the formulas in each cell (there is no password).

What is the best way to hang an off-center-fed dipole or windom antenna as an inverted-V? Should you hang the feedpoint at the apex, or hang the center of the antenna at the apex?

From an electrical standpoint the best way is to hang the center at the apex. That is where the current is at a maximum on the lowest resonant frequency. But that leaves all the weight of your balun, coax, and (in the case of a New Carolina Windom) RF choke unsupported by anything but the antenna-wire itself. So from a mechanical standpoint the best way is to hang the feedpoint at the apex, with all that weight hanging straight down from the hanger. Either way it’s a trade-off.

I think it makes sense to hang the feedpoint at the apex if the angle of your V is reasonably broad. The mechanical benefit outweighs the electrical cost in this case. As you can see in this diagram, you really don’t give up much height at the center of the antenna. My own 40m New Carolina Windom, with the longest leg at 74^o from vertical, sacrifices only 2.3′ at the center of the antenna. Even if it were cut for 80m the sacrifice would only be 4.5′. A 160m version (I know of one fellow who plans to build one!) would give up almost 9 feet, though. You might want to hang the center at the apex in that case, unless it’s already so high that 9 feet doesn’t matter much. You can always figure out a way to support the feedpoint in some way if you need to.

This changes if you mount your V with a narrow angle. Dropping the longest leg to 45^o from vertical would cost me 6′ on my 40m New Carolina Windom! In that case it would probably make more sense to hang the center at the apex.

The way to calculate this is shown in the figure above. Notice how I labeled the sides of that triangle with “H” and “A?” Now why did I do that? Glad you asked! The “H” stands for “hypotenuse” and the “A” stands for “adjacent” — adjacent to the angle of 74^o in this triangle (your own angle may be different, of course). Just remember this sentence: “Oscar And Ole Have Huge Appetites.” (Up here in Minnesota we all love that name Ole, don’t ya know!) That will help you remember the way to calculate the sine, cosine, tangent, arcsine, arccosine, and arctangent of any angle. “O” stand for opposite (the length of the side opposite the angle you’re dealing with), “A” stands for adjacent, and “H” stands for hypotenuse:

Oscar And Ole Have Huge Appetites!

So to figure out the height of the apex above the center of my antenna, I figure:

A/H = cosine(74^o)
A = cosine(74^o)*H
A = 0.276*8.5′ = 2.3′

There you go! Of course, you’ll have to know the angle to figure this out. To see an example of that calculation, check out my previous post.

From the “Oh, How Cool is That?!” department, is a video to round out a week’s worth of Ham Radio videos, showing an iOS device, (iPhone,iPod Touch,iPad) decoding an SSTV signal. I have seen a bunch of Ham Radio apps on the iTunes App store, but I seemed to miss this one. According to the link in the video’s description, the SSTV Decoder app is made by Black Cat Systems, who also make a few other Ham Radio programs for Macs. The webpage says “.. Just connect it to an HF radio (or even set it next to the radio’s speaker), tune in an SSTV frequency, and watch the pictures.” From the video I didn’t see a directly connected cable from the iPod Touch, so I’m guessing that they are using a 4th Generation iPod Touch with a built in microphone and have it sitting close to the radio to hear the SSTV tones. Still, it looks like it received a nice picture. But they could also have been replaying pre-recorded picture on the device too. Either way, it’s cool!

73.

Rich also writes a Tech blog and posts stories every Tuesday and Thursday on Q103, Albany’s #1 Rock Station website, as well as Amateur Radio stories every Monday thru Friday on AmiZed Studios and hosts a podcast called The Kim & Rich Show with his fiance’ Kim Dunne.

Today is my wonderful wife Olga’s 60th birthday. Without her amazing help and support I don’t know if I would have the strength to cope with this brain tumour. I keep up the fight so that I will still be here to help celebrate the next one. Happy 60th birthday, Olga!

With propagation on 10m being so good I have been trying to make some contacts using the Albrecht AE2990AFS multimode handheld using a whip antenna. No luck so far, however.

One annoying aspect of the Albrecht is that it tunes in 10kHz steps since it is essentially a CB radio. There is a step control that lets you choose 1kHz or 50Hz tuning steps, but this only works within one 10kHz or 1kHz range. You can’t tune the whole band in these smaller steps. Not only that but the clarifier control (better known to hams as RIT) shifts only the receive frequency and doesn’t have a centre detent so you can never be sure you are calling a station on his exact frequency.

An eBay seller of the Super Radio SS-301 – which seems to be the same radio as the Albrecht under another name – claims that the clarifier works on both TX and RX. So there is presumably a modification that would make the clarifier work like a VXO. But I’m darned if I can find any details of it. Has anyone made such a modification to this radio?