[600MRG] New Part 5 Grant

[jrusgrove at comcast.net]

Not a new idea ... WE2XGR/2 worked James WD2XSH/35 in South Dakota back on 1/3/2010. James was 
running a full sized dipole at low height (30' IIRC). His signal strength was 'marginal'.

Jay W1VD  WD2XNS  WE2XGR/2




----- Original Message ----- 
From: "D.J.J. Ring, Jr." <n1ea at arrl.net>
To: "600 meter group SHMRG" <600mrg at w7ekb.com>
Sent: Wednesday, May 15, 2013 9:14 PM
Subject: Re: [600MRG] New Part 5 Grant


> Fascinating idea, Brian!
> 73
> DR
>
> Low Profile LF and MF antennas
> Proposed Research and Experimentation
> Brian Pease, W1IR, Amateur Extra
> 2/27/13
> Most radio amateurs assume that verticals are the only practical
> antennas for long distance
> communication at low frequencies. Simulations of antenna performance
> in the proposed 135.7 –
> 137.8kHz and 472 – 479kHz Amateur Radio Bands show that resonant
> horizontal dipole antennas
> located very close to the ground (but with no ground system at all)
> have significant vertical E-field
> radiation and can potentially perform nearly as well as a 15 meter (50
> ft) top loaded vertical with a
> ground system. This is especially true in locations with poor ground
> conductivity where vertical
> antennas tend to perform poorly. The dipoles are directional, with
> maximum vertical radiation off the
> ends. In one simulation, a resonant dipole at 475kHz positioned 2
> meters (6.5 ft) above the ground
> with ground conductivity of .002 S/m created a vertical Electric field
> off it's ends only about 3dB less
> than the 15 meter vertical mentioned above. Even a dipole 2 inches
> above the ground radiates
> significant energy in simulation. The Dipoles are also broadband. The
> 475kHz dipole 2 meters off the
> ground has 30kHz bandwidth at the 2:1 SWR points, far wider than the
> proposed band.
> Resonant dipoles close to the ground are much shorter than in free
> space, ~220 meters (715
> ft)for the dipole 2” above ground vs ~315 meters (1033 ft) in free
> space. They can be shortened further
> by adding capacitive loading to the ends, loading coils, or with a
> matching network at the center. For
> very short antennas, the ends can be grounded, but this can add
> considerable loss especially where
> ground conductivity is poor.
> I think that if these LF and MF bands become reality, these simple low
> profile antennas could
> allow many hams (who have some space) to experiment with LF or MF that
> otherwise would not
> attempt it because of the hassles and expense of a tower, ground
> radial system, top-hat, and tuner.
> These antennas can be run along the top of a fence or attached to
> trees while standing on the ground.
> Cheap Aluminum electric fence wire and insulators can be used. I have
> the space to conduct some
> experiments.
> I propose to attempt the following:
> •
> Simulate several more antenna configurations, heights, and ground
> conductivities for each band
> using the NEC4 method of moments program.
> •
> Measure the actual conductivity of the ground where the antennas will
> be erected to better
> estimate expected performance.
> •
> Erect a limited number of antennas (one at a time in the same
> location), tune them, and measure
> and record lengths, bandwidths, etc. All antennas will be “in the
> woods” well below the
> existing tree canopy.
> •
> Transmit a carrier of known power from each antenna and measure the
> vertical field strength off
> the ends and sides in the far field several km away, using a shielded
> Fairchild calibrated loop
> antenna and a Rycom portable Selective Voltmeter with a preamp. Based
> on the simulations,
> the initial transmit power will be adjusted for an expected EIRP of ~1
> Watt or less.
> •
> Compare measured to simulated performance and select the best designs.
> •
> If possible, use existing signal “grabbers” linked to the internet, or
> direct contact with other
> experimental stations to demonstrate long distance communication.
> Possible modes are CW,
> PSK31, and the narrow band weak signal FM digital modes created by
> K1JT, especially WSPR
> and his new JT9-1 mode designed especially for LF/MF communication.
> I have the following equipment on hand now:
> •
> Materials to erect the antennas.
> •
> A homebuilt 25 Watt Class E amplifier for 472-479 kHz.
> •
> A Hafler P3000 300 Watt linear audio amplifier suitable for 135.7-137.8kHz.
> •
> An HP3586C Selective Level Meter as a receiver, with an RF output
> suitable to drive the
> amplifiers for the field strength testing.
> •
> A homebuild active loop antenna to receive these bands to select clear channels.
> •
> A Trimble GPS frequency standard to lock the 3586C frequency to a
> fraction of a Hz accuracy.
> •
> A Fairchild calibrated loop antenna for the field strength measurements.
> •
> A battery operated Rycom 3121B Selective Level Meter with preamp for
> field strength.
> •
> Equipment to assemble an RF impedance bridge for tuning/measuring the antennas.
> •
> An Advantest R3361A Spectrum Analyzer for measuring harmonic output of
> the amplifiers, etc.
> •
> An IC-703 as a low level (SSB) signal source for the digital modes.
> •
> A laptop computer with software to send and receive the digital modes.
> I will need to fabricate a ~100 Watt amplifier for 472-479 kHz, with
> adjustable power level, and
> a forward/reverse RF power meter that covers both bands. I will need
> to assemble and calibrate the RF
> impedance bridge.
>
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