[BC] Slant wire feeds vs series fed

[Phil Alexander]

On 26 Jan 2006 at 10:57, Scott Bailey wrote:

> Phil,
>     If a exsisting daytimer, wanting to (or needing to) go to a slant 
> wire antenna system, will they grant that? 

I tried finding the rule that says in essence that they won't approve
a slant wire for nighttime service, but without success. I found this
a year or two ago, but I don't remember the details. It did appear to
me that there was no prohibition against using a non-directional
daytime slant wire fed grounded radiator.

As I recall the rule, I think an application to feed a tower with
a slant wire would be approved, but it might require some dialog
with the FCC staff.

For example, suppose you had an AM/FM; the AM was erected in the 
late '40's with a 200 or 250 ft tower. Further suppose you that
when the FM mileage separations and classes began in the '60's
your station was allocated a class A FM and a 325 ft grounded
tower was erected nearby for the FM. That tower should have guy
wires with insulators and probably would have had a very simple
slant wire detuning kit so as not to interfere with the AM
coverage, or maybe no kit if it was in a direction that was not
important and it was a couple of wavelengths away from the AM
tower. Now, fastforward to the present when a mini-tornado blows
through and takes the AM tower down. As an emergency measure, you
feed the FM tower with a slant wire and apply for an STA to do
that.

After all the dust settles, you decide to put in a permanent ground
system around the FM tower and feed it with a slant wire on a 
permanent basis. Given the proper engineering studies showing the
proposed power input to the taller tower gave the same contour as
before or that the enlarged contour did not interfere with co or
adjacent channels, I suspect they might grant the application.

Considering the cost differential between a slant wire and a skirt
kit, I'd take the slant wire if they would grant it.

> Now say if the daytimer 
> has flea-power, say 2-10 watts, would they still allow the daytimer 
> to use the slant wire feed?

If you mean for nighttime, I know some cases where a grandfathered
Class III-D was granted a nighttime power although it used a slant
wire feed. Usually these are in the 5 to 75 W range.

> I've seen where this has been done on a emergency basis, and it 
> worked just as good, or better than the old 1/4 wave series feed tower.
> I wonder.....what stations in the US are still using slant wire feeds?

Yes, it can be simple and quick to set up, in fact deceptively so.
If you look at non-DA stations of 1 kW or less granted before about 
1955, you will probably find quite a few of them. Several have been
mentioned on the list, and I'm sure there are more out there. 
 
>I'm using a unipole on my AM, but the slant wire, seems much more simple!

To that, I've got to say yes and no. Slant wires can be *very interesting*
challenges to set up for the inexperienced, and that is nearly anyone
below the age of retirement today. The things work so well that simply
running a plant with one does not provide much experience. It is only
in tuning them, using a cold bridge, that you begin to get an idea of
what they are all about. Some hams know the principle as do some from
the HF field where they are more widely used. The trick is getting
a good impedance with a desirable resistance and having an inductance
that is workable with a simple series capacitor. Typically, it is
possible to hit 40 to 50 ohms with 500 to 1000 ohms inductive reactance.
The second trick is having a good ground strap from tower base to
feed point and transmitter. Note that it is possible to feed a slant
wire feed point with 50 ohm coax and simply have a variable vac. cap.
and current meter at the feed point. The transmitter can be at the
other end of the coax a quarter of a mile away if necessary, although
feeding directly out of the transmitter house is preferable.

Really, the key is having someone set it up who understands it, which
is equally true of a skirt. Neither one is as simple as it looks, and
experience with one does not translate too well to the other. I like
them better than skirts, because they have a sort of simple purity
that can give excellent efficiency if they are correctly set up. All
it is, is a wire between two points. However, finding the BEST two
points is the *interesting* part. <g>


Phil Alexander, CSRE, AMD
Broadcast Engineering Services and Technology 
(a Div. of Advanced Parts Corporation) 
Ph. (317) 335-2065   FAX (317) 335-9037





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