May 2014 Archives

The Untenna, A Direct Driven Ring Radiator (DDRR)

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The Untenna is a direct driven ring radiator (DDRR) which was manufactured in New York by ComRad Industries, Inc. I believe ComRad is out of business, but I may be wrong. Here is some information I found that I scanned from ComRad:

It's not an antenna manual, but one can note that the antenna is simple in construction. It was invented by Dr. Joseph M Boyer and patented in 1964:

The antenna was published in 73 Magazine. I have pulled the JPGs from The Internet Archive Project and combined them into a single PDF linked below.

Surprisingly, this early horizontal antenna was cited:

The antenna shows up in the History of The Bell System, a multi-volume set of books illustrating technological achievements of the Bell Telephone Company.

Other information on the DDRR:

It appears the DDRR has been used for every imaginable purpose, including NVIS. It is somewhat related to the magnetic loop, which shares many aspects of the antenna.

If you're in need of ideas:

Battery Size Requirements for Communications

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This is on the GROL exam, but...

If the duty cycle is 10%, and the radio draws one ampere on receive and twenty-five amperes on transmit, how much battery capacity is needed to provide support for twenty-fours?

90% of the time, the radio will draw 1A.
10% of the time, the radio will draw 25A.

So the average then becomes:

Ia = (1 * 90%) + (25 * 10%)
Ia = (1 * 0.90) + (25 * 0.10)
Ia = 0.90 + 2.5
Ia = 3.4 A

Since the system will draw this more or less continuously, the battery should be sized accordingly. There are caveats however. Most batteries react negatively if the discharge rate is greater than 50% of the amp-hour rate. For instance, attempting to draw 100A out of a 100Ah battery for one hour will only result in a usable capacity of 50Ah. This is because of internal cell resistance.

Ia * time = capacity required
3.4A * 24h = 81.6Ah

Additional capacity should be provided so the battery is never fully discharged, and to cope with temperature extremes which limit the ability to both charge and discharge the battery.

If the discharge rate exceeds 50% of the battery capacity, derating (additional capacity) will be necessary to provide enough power to run the load.

Most batteries are specified on a twenty hour (20h) discharge cycle, not a twenty-four hour (24h) cycle. Therefore an additional 20% is required if calculating based on battery data; the 24h rate requires 120% the battery of the 20h rate for the same current draw, if using back of the envelope calculation. For calculations like the above, this issue is not considered because the time for discharge is defined.

A good safety margin is 125% - 250%. If 81.6Ah is required, 100Ah will allow for some reserve capacity, and 200Ah will allow for the temperature dropping below 60 degrees F or exceeding 85 degrees F.

Always remember to keep your batteries off the ground, and not sitting on a metal plate as coldsinking effectively removes capacity.

Additional resources:

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