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Author Topic: EIRP for the "600 meter" Band  (Read 2719 times)
RFRY
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« on: May 09, 2012, 12:23:13 PM »

The FCC may permit use of the band 472-479 kHz by licensed amateur radio operators, using either 1 watt or 5 watts of effective isotropically radiated power (EIRP).

EIRP is the product of the power applied to the antenna feedpoint and the antenna system gain, where the antenna system gain is referred to that of an isotropic radiator.  An isotropic radiator is a theoretical source that radiates equal power in all directions.

Knowing that EIRP this will require knowledge of the net gain of the antenna system.  NEC software will be useful in determining that gain.

As an example, for a 15 meter high monopole on 475.5 kHz with a total of 50 ohms of system loss for the loading coil and r-f ground connection, NEC shows about  -18.35 dBi for the peak gain of the antenna system.

The link below then is useful to calculate the transmitter output power needed to produce a given EIRP with that antenna system.

To produce 1 watt EIRP with the above antenna system requires about 68.4 watts of Z-matched power at the antenna input terminals.  For 5 watts EIRP it would be 5X that, or 342 watts.

http://www.csgnetwork.com/antennaecalc.html
« Last Edit: May 11, 2012, 01:41:22 AM by RFRY » Logged
RFRY
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« Reply #1 on: May 10, 2012, 06:24:47 AM »

Here is a link showing the estimated groundwave field intensities from 5 to 35 km for 1 watt EIRP on 475.5 kHz, and an earth conductivity of 5 mS/m, d.c.13.

http://i62.photobucket.com/albums/h85/rfry-100/GW_Field--1W_EIRP_476kHz.jpg
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W0BTU
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« Reply #2 on: May 10, 2012, 07:17:47 PM »

As far away as we can hear those 10 watt highway traffic information transmitters along the interstates on 530 kHz AM, the 600 meter band ought to be a lot of fun with that kind of EIRP.

You might find this thread interesting, near the end: http://www.eham.net/ehamforum/smf/index.php/topic,82862.msg595256.html#msg595256 which discusses those and a web site that lists them.

I'm not certain how the 600 meter antennas that hams are allowed to use compare with what those stations use. But I think I read that we can use a much bigger antenna (not to mention top loading). With the low ground wave attenuation on 600 meters, and using different modes, just imagine the possibilities. :-)
« Last Edit: May 10, 2012, 07:24:52 PM by W0BTU » Logged

RFRY
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« Reply #3 on: May 11, 2012, 06:45:24 AM »

I'm not certain how the 600 meter antennas that hams are allowed to use compare with what those stations use. But I think I read that we can use a much bigger antenna (not to mention top loading)

AFAIK the FCC has not set or proposed any antenna definition/limit for this band.

But if the FCC sets an EIRP limit for it, technically it wouldn't matter what combination of transmitter power and antenna system gain is used, as long as the EIRP from that system doesn't exceed the FCC limit.

This is a similar situation as with FM/TV broadcast stations, which are licensed for a certain radiated power.  They can achieve that power using a higher power transmitter with a lower gain antenna, or vice versa.
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NM3G
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« Reply #4 on: May 11, 2012, 09:05:17 AM »

During my career in the USCG, I was involved with MF radio beacon maintenance and upgrade efforts. The antennas used varied from a 35' Shakespeare Model 222B, to an 80 foot lattice tower that was base fed and diplexed for 306 kHz and the 2 MHz HF AM band. I also was involved in replacing an 80' monotube antenna with an 80' vertical with a Nautel radio beacon transmitter and automatic antenna tuner (more on that later). Shipboard MF transmitters with a remote antenna tuner to an inverted "L" rounded up my experience

In all shore installations, a very good buried ground radial system was used  ... radials were typically 10% longer than the antenna, and were at 2° spacing (if my memory serves me correctly). The shipboard installations worked against the steel / aluminum hull and the ocean.

The 306 kHz radio beacon was part of a 6-station sequenced network on Lake Ontario. This beacon had an amplifier with a pair of 4-125s ... not sure about the output power as we measured and adjusted for a field strength at a fixed distance.

The field strength was established to provide radio beacon service on Lake Ontario, but SWL (or would that be LWL?) reports from New Jersey, CT, and several from the mid-west demonstrated the night time coverage.

In the installation with the automatic antenna tuner, we found that the tuner would  not function below 10 watts into the tuner ... and if we ran at this power level, our field strength measurements were well above the required/permitted level.

The reason for the auto tuner is that the antenna resonance changed dramatically with the weather ... fog has a serious detuning effect on the antenna system ... the auto tuner provided a constant field strength under all weather conditions (you really need the radio beacon when it's foggy!).

As with all technology, most (if not all) remaining radio beacons are now used for DGPS (differential Global Positioning Satellite) offset correction broadcasts that provide real-time position accuracy.

What does all of this have to do with the 600 Meter allocation?

Antennas do not have to be 1/4 wavelength to function ... even a short antenna will provide good coverage IF the ground plane is extensive.

Antenna tuning will be affected by the environment; plan on monitoring and adjusting a tuner when operating.

Existing insulated vertical antennas can be easily matched ... just don't put the coupling network inside a metallic cabinet. Fiberglass works much better ... and it really needs to be at the antenna base ... not located at the transmitter end of the feedline.

Have fun with this allocation ... I'm thinking that a very narrow, low signal mode such as PSK31 or JT65 will show the utility of this narrow, low frequency band.

73
Rick
NM3G
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RFRY
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« Reply #5 on: May 11, 2012, 09:42:39 AM »

Existing insulated vertical antennas can be easily matched ... just don't put the coupling network inside a metallic cabinet.

Also watch out for the base voltage on the monopole.

The link below shows the parameters for the system defined. With an EIRP of 1 watt including the earth reflection, the base voltage is close to 2,300 volts (see the block highlighted in yellow).

http://i62.photobucket.com/albums/h85/rfry-100/600-m_System.gif
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W0BTU
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« Reply #6 on: May 11, 2012, 03:54:57 PM »

AFAIK the FCC has not set or proposed any antenna definition/limit for this band.

Yes. I engaged the "post" button before I put the brain in gear when I said that.  Wink

Using CW and PSK31, it would be interesting to see some estimates of the distances that might be covered between two stations in quiet locations using 900' Beverage antennas (the longest I could possibly have here) for listening.
« Last Edit: May 11, 2012, 03:59:55 PM by W0BTU » Logged

RFRY
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« Reply #7 on: May 15, 2012, 05:49:13 AM »

Following is the real part of the base impedance on 475.5 kHz, calculated by
NEC-4 for a "tee" antenna system consisting of a 10-m vertical conductor
connected at its top to the center of a 20-m horizontal loading wire, and
base-driven against a set of 16 horizontal radials each 10-m long, buried
0.1-m in earth of the conductivity values shown:

  mS/m              ohms
    0.5                  46.5
     2                   12.6
     5                    5.7
    10                   3.3
    15                   2.5
    30                   1.7
 Perfect               0.1 (Rr)

The radiation efficiency of each of these systems = Rr / (Rr + Rloss).
The system loss total includes the loss of the matching network needed
to resonate the system, and match it to the transmission line from the
transmitter.  Matching loss will vary according to the design and
construction of the network, but it will need to offset the ~2,200 ohms
of capacitive reactance at the feedpoint of the tee.

When the matching network loss is known, the transmitter power output needed
to radiate a given EIRP for these conditions (including the ground reflection)
can then be calculated.
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