My attempt to explain EIRP, or why EIRP should not be confused with transmitter power...
 

EIRP is not the same thing as Transmitter Output Power (TP), the two
different measurements are only nominally related.

Assuming the wire or duct carrying the RF energy from the transmitter has
ZERO REISISTANCE, and no HYSTARHESIS (Z0) effects:

TP (will never exceed) EIRP, assuming the antenna is a single point radiator
(or an omnidirectional dipole for longer frequencies).

Example of almost 0 db directional gain (AM broadcasting):
http://cbc.am/fk.htm
-- my goal here is to have 26 dbi gain, not omidirectional gain.

An example of 16 db directional gain (shortwave broadcasting):
http://cbc.am/cbc.htm
-- (EIRP) gain is spread out over a 40 degree region
-- notice the low (50 kw vs 500 kw) power requirements due to the
directional gain aka EIRP

Classical directional gain in a 30 degree region:
http://cbc.am/rci-bc.htm

With enough radiators arranged in the right order, 26 dbi gain is easily
obtained -- and the need for extremely high power transmitters is reduced.
Directional gain antenna systems make modern broadcasting possible...

With enough radiators arranged in the right order, 26 dbi gain is easily
obtained -- and the need for extremely high power transmitters is reduced.
Directional gain antenna systems make modern broadcasting possible...

26dBi is a LOT of gain- especially if you are talking about HF- as your
references are. Obviously, the array would have to be fixed as it would need to
be in excess of 9 wavelengths long if it were a Yagi (arguably the highest gain
array for its size). At 7MHz this would be somewhere around 26 elements each in
the neighborhood of 66' and occupying a total length in excess of 1200'.
Without going to my texts, I would guess the 3dB BW of such an array to be in
the 10 degree region- not much coverage.

Dale W4OP

What sort of gain do those curtain arrays have that the international broadcasters use?

I understand that in Siberia that there is such an HF curtain array that has
26dbi gain.
I guess is operates 9 mhz ... 21 mhz bands, but information on former USSR
curtain array antennas in Siberia is quite limited as GOSTELCOM (the Russian
Telecom PTT) that runs these sites is mum on the technology.

All of these directional arrays are slewable, typically (- / +) 15 degrees,
giving a 30 deg coverage region.
VOA Delano is the nearest equivalent in the west, it is a HRS 12/6/1. TCI
sells the base antenna, but you will have to look in the data sheets area of
the website because the document is not mounted with the main HRS antennas.

A full blown HRS 12 / 6 / 1 goes for about 12,000,000 USD -- dammed cheap!

The most amazing thing is that there are MW transmission sites in Russia
with 26 dbi gain -- and designed for skywave reception.

PS: these sites can be used for other uses than SW broadcasting like SW
based RADAR, and Ionspheric research.

-- text --
With enough radiators arranged in the right order, 26 dbi gain is easily
obtained -- and the need for extremely high power transmitters is reduced.
Directional gain antenna systems make modern broadcasting possible...

-- reply to text --
26dBi is a LOT of gain- especially if you are talking about HF- as your
references are. Obviously, the array would have to be fixed as it would need
to be in excess of 9 wavelengths long if it were a Yagi (arguably the
highest gain array for its size).

At 7MHz this would be somewhere around 26 elements each in the neighborhood
of 66' and occupying a total length in excess of 1200'. Without going to my
texts, I would guess the 3dB BW of such an array to be in the 10 degree
region- not much coverage.

Dale W4OP

I understand that 12 dbi to 20 dbi is typical gain for SW curtain antennas.

"Brenda Ann" wrote:
What sort of gain do those curtain arrays have that the international
broadcasters use?

I suspect such an antenna is HRS 12 / 6 / 1 or possibly HRS 18 / 6 / 1,
using horizontally placed dipoles as is typical with HRS antennas.

See:
CBC.am/HR.htm
-- for a guide to HR antenna types.

I understand that in Siberia that there is such an HF curtain array that
has
26dbi gain.
I guess is operates 9 mhz ... 21 mhz bands, but information on former
USSR
curtain array antennas in Siberia is quite limited as GOSTELCOM (the
Russian
Telecom PTT) that runs these sites is mum on the technology.

However, the necessary size and beam width characteristics can be
calculated
fairly directly.


The most amazing thing is that there are MW transmission sites in Russia
with 26 dbi gain -- and designed for skywave reception.


If you start with one halfwave dipole, you get 2.14 dBi gain.

If you double the number of these antennas, with suitable spacing
to ensure their capture areas don't overlap, you can increase the gain
by a maximum of 3 dB, with 2.5 being a common case due to losses in
the system.

If we are shooting for 26 dBi, you need 26 - 2.14 = 23.86 dB gain

Doing this would require putting up 243 of these dipole antennas.


If instead, you used an array of yagi antennas, each with 8 dBi gain
(fairly large, but probably possible), you would 'only' need 63 of them.


mikehack wrote:
With enough radiators arranged in the right order, 26 dbi gain is easily
obtained -- and the need for extremely high power transmitters is
reduced.
Directional gain antenna systems make modern broadcasting possible...


Antennas with that much gain are not particularly useful for
broadcasting,
since the beamwidth is so narrow. Lining up a row of vertical halfwave
dipoles
would get a pattern in elevation similar to a single dipole, and would get
all
the gain by squeezing the azimuthal beamwidth down to a degree or two.

My calculations show that 26 dBi has a symmetrical beamwidth pattern
of about 10 degrees. Any increase in beamwidth (such as arrays of side
by side antennas would have) would require a reduction in the azimuthal
beamwidth.

There are folks who are really good at this -- however, if you want
their
services, you probably would have to pay them.


So, Mike, what are these postings about? They didn't seem to be a
response
to postings in the newsgroup where I found them.

http://CBC.am/ wrote:
I suspect such an antenna is HRS 12 / 6 / 1 or possibly HRS 18 / 6 / 1,
using horizontally placed dipoles as is typical with HRS antennas.

hoax -