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*To*: "Bill O'Neill" <billo@shoreham.net>, "Boston Radio Interest" <boston-radio-interest@bostonradio.org>*Subject*: Re: Standard vs. Augmented?*From*: "Dan Strassberg" <dan.strassberg@att.net>*Date*: Sun, 7 Oct 2001 10:21:26 -0400*References*: <002101c14e96$5a0ac240$19fd90d0@003774259>*Sender*: owner-boston-radio-interest@bostonradio.org

A more pertinent question is what the difference is between the theoretical pattern and the standard pattern. I had thought that the standard pattern _was_ the theoretical pattern, but I've been told that it's not, and I don't know the difference. In the pattern data in the FCC AM database for most stations, there is a column called (if I recall) expected values. These seem to be the standard values at each azimuth adjusted by some constant factor (I think 105% of the corresponding standard value). I assume that the expected-values column is intended to account for such effects as the seasonal variation in soil conductivity. I believe that a 5% correction doesn't come close to accounting for such variations. Then there is the column of augmented values, which appears in the data on many--but not all--AM patterns. Augmentations are established after the proofs of performance have been completed following construction of the array. After the engineers have done their best to bring the array into specification, they give up and apply for one or more augmentations to provide a description of the field vs azimuth that more closely approximates the array's measured performance. In gneneral (though, again, not always) the designers and the FCC bother with augmentations only in directions in which the augmentations could make a difference--that is, in directions in which the augmentation could affect protections to other stations. Each augmentation has an azimuth, a magnitude, and a span. I've seen patterns with upwards of 20 augmentations--not 20 azimuths with augmented values, but 20 augmentations each having a span of as little as 10 degrees and as many as maybe 50 degrees. It's not uncommon for several augmentations to affect the pattern's augmented values at particular azimuths. Each augmentation follows a formula with a specific rate of drop off vs azimuth in the effect of the augmentation. The effect is greatest at the augmentation's central value and the drop off is based on the ratio to the augmentation's span of the difference between the actual azimuth and the augmentation's central azimuth. The whole scheme seems to me to be excessively complex--involving the use of mathematics to describe an effect that probably would best be described by tables of augmented values constructed from measurements. There's another fudge factor that I don't understand at all. Many--but not all--AM patterns have something called a Q-factor. It applies to entire patterns. I haven't a clue about the origin or the effects of Q-factor. Current ratios in towers are specified, as you figured out, with respect to the current in a reference tower. Usually one tower is shown with a ratio of 100%, though I'm not sure that any tower _has_ to have a ratio of 100%. Nor am I sure that the tower that is used as the current reference is always the one that is used as the location reference. Most arrays (but again not all) use one tower as a location reference, but some arrays (WMKI's is one) use as the location reference a point at which there is no tower. Many complex arrays use a combination--some tower locations are described with respect to a reference tower and others are desribed with respect to some other tower or towers. Degrees are used in three ways in the array specifications. Azimuth is specified in degrees of compass heading, where a circle is divided into 360 degrees and an azimuth of zero always corresponds to true north. (The number of degrees in a circle and zero equalling true north may be the only parts of array specifications that apply to all arrays ;>) The phase of the current in any tower applies to the delay (as a portion of the carrier-frequency cycle) in the current in one tower with respect to the current in the reference tower. One cycle equals 360 degrees (something else that's always true ;>) It seems to me that a specification of tower current that did not include phase as well as magnitude would be meaningless. Finally, as you correctly surmised, tower heights and spacings among towers are specified in degrees, where one degree is 1/360 of the station's wavelength--_almost_ always assuming that the velocity of propagation is that of light in free space (299.8*10^6 m/sec). It turns out that for some AM antennas (skirt-fed folded unipoles being the best example) the velocity of propagation in the antenna is somewhat lower than that of light in free space. This little-understood effect has apparently resulted in at least one folded-unipole installation (WOLF, Syracuse) delivering efficiency so much lower than the predicted value that the 5/8-wave tower, which had a predicted efficiency of 440 mV/m/kW unattenuated at 1 km, actually delivered less than the Class C minimum of 241 mV/m. That meant that 1 kW into the supposedly super-efficient antenna was actually equivalent to less than 300W! As we say in high tech, "oops!" -- Dan Strassberg, dan.strassberg@att.net 617-558-4205, eFax 707-215-6367 ----- Original Message ----- From: Bill O'Neill <billo@shoreham.net> To: Boston Radio Interest <boston-radio-interest@bostonradio.org> Sent: Saturday, October 06, 2001 2:38 PM Subject: Standard vs. Augmented? > Checking out different AMer in the database and some patterns are listed as > "augmented" and some as "standard." Unashamed to admit how little I know in > these areas, here I go: > - what's the difference? > - What's "degrees" - something to do with tower height, right? > - Some towers list phase and ratio and some just phase? > - Orientation: to the reference tower, right? > > Bill O'Neill

**References**:**Standard vs. Augmented?***From:*"Bill O'Neill" <billo@shoreham.net>

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