Saturday, November 17, 2012

Some Thoughts on What to "Hang", and Where

Some Thoughts on What to "Hang", and Where

You've just arrived at your potentially "new" QTH for the first time, and decide to do what most hams do; look around for possible antenna sites! Let's see... Would a tower and beam install here? Well, you'd better see how far away it is to potential electrical hazards like overhead power lines and their associated drop-lines to the house, garage, or out-building. The height of the tower, and width of the beam elements come to bear when distancing from those hazards. Should it/they fall over, or the elements come into contact, it's BIG trouble, or even injury, and/or death!
Now it's time to investigate possible sites for other/alternative antennas. Suppose your mindset is on a nice ¼ wavelength vertical with radial system (Groundplane). Is the roof of the dwelling an option? Sometimes your XYL will permit such an installation, but will your subdivision or housing association? If they're not issues, then the roof might be a great place for a ground plane... The radials can droop most times, and even a multi-band vertical rests well "up there..." Cut a few radials for each band ("snake" them if you have to), or use an AV-14RMQ Roof-Mounting Kit when possible, and you'll probably be happy with the performance. Be sure and create a good path for lightning to terminate! Remember, the XYL...
Another place for the ¼ wavelength vertical, or an inverted L with radial system, is ground-mounted... First, it's time to check the soil condition(s). If it's high-resistance, consisting of a lot of silicates (sandy) and mica-shist (insulators), then I would think twice unless I could go to a ½ wavelength installation (voltage-fed or MFJ-1796,98 series). With poor ground conditions, you'll never have an efficient Marconi (current-fed) system, even though your "match" may be 1:1; losses are too great. So, the voltage-fed ½ wavelength vertical or inverted L may be the solution; sure would be efficient in these soil conditions compared to the current-fed "Marconi"... Use an L-Network at the base of the vertical (or vertical section) and you'll get the match you want, and some nice bandwidth to tune as well.
If good soil ground conditions exist, then go for your home-built or commercial antennas (MFJ-1792; 1795 series; or Hy-Gain series) using a good ground plate as well (MFJ-1904). Install the ground radials for best performance, and you're on the air!
If you find that a tower or pole in the yard isn't an option, and an inverted V hasn't a place to hang, or the coax can't come down in the center of the yard, then try an end-fed antenna. The End-Fed Zepp (MFJ-61xx series) is a great radiator, and doesn't demand a lot of height. Now, it's time to look for places to erect "poles/masts".
If you have a privacy fence (or any fence for that matter), and it follows the property boundaries to an extent, then try a couple of masts at ~30 feet high or so; even ~20 feet will do in most cases... Guying may not be an issue if you can affix to a sturdy privacy fence, and don't try to hang heavy gauge wire and traps. Use #18 copperweld for your antenna radiator; light-weight and strong. Sturdy masting helps eliminate the guying requirement as well. Once you establish the maximum distance between "poles" or other tie-off points such as structures (ends of the house) or trees, you can determine what antenna you can "hang".
The End-Fed Zepp is available in a single-band configuration (MFJ-61xx series), so you only need to attach the coax, and operate! For multi-band use, run the ladder-line into the shack or to a 4:1 balun, with coax to the shack, and you'll tune most bands. The inverted L has already been discussed, but finds a home close to structures just fine. So, using one next to a pole is quite acceptable.
Even antennas with some degree of gain can be erected using the schemes already mentioned. The 2-element collinear array (MFJ-62xx series) can find a nice place to hang, and give a bit of gain too (See Antenna Talk #1).
How about dropping that 17 or 20 meter, or even 30 or 40 meter ¼ wavelength vertical down from a run of horizontal line between two supports? Or, even from a horizontal section of an existing antenna? Place an insulator on the wire or line, and "hang" the vertical antenna (up to 30 feet or so) from that point! Then, install your ground system and/or matching device right there (at the hang-down point). It may even help your radiation from the horizontal antenna!
Look for a basement window retaining wall as a good ground connection as well if it is indeed metal. The deeper the wall, the better the ground. It's a good location for a feedpoint of a ¼ wavelength Inverted L. You'll find this in Townhome/Condo situations most often. Shortened wire antennas (MFJ-17754; 17758) can be located where not much horizontal distance is available. Use an external antenna coax switch (Ameritron RCS series) to select your antenna of choice.

1 comment:

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