Optimizing MURS Dakota Alert Sensors by Tunnel Rabbit for Survival Blog
To begin, here’s some ground thruth on perimeter security: Security will be Job One. Everything else supports that objective. Manpower for most tasks will be greatly lacking. Every trick, hack, or tactic should be considered. If we don’t see’em, hear’em or smell’em coming, then it is over before it starts. You lose.
Organizing with your community is the best defense for those without their own manpower. Defend at a distance, not at the mail box. Don’t let them into the area in the first place. Thus, potential intruders will be reduced to a few potentially lawless neighbors.
One of the best plug-and-play force multipliers–often recommended by JWR–is the MURS band Dakota Alert system. We all should know about those by now. If not, then please see a video on it.
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Although only a 1/2-watt transmitter with a limited range, external antennas can greatly improve the distance at which Dakota Alert sensors can be deployed. I make my own antennas, but I cannot beat the least expensive and most effective external antenna on the market.
When ordering these antennas, request the longest continuous cable length of at least 15 feet or more, if possible, specify the cable end, and the frequency it should be tuned for. In this case, a good center frequency should be 153.500 Mhz. A less expensive DYI antenna is a dipole made from RG58 coaxial cable, but you’ll need a Standing Wave Ratio (SWR) meter. The least expensive one on the market is the Workman 104.
I can make one of these antennas inexpensively by cutting a 20′ cable with two PL259 ends, and make two antennas for about 10 bucks each or less. Here is how.
And here is how to use an SWR meter when making antennas.
MILKING EXTREME RANGE
To squeeze every bit of range out these, put it on a yagi, or moxon antenna up high as possible, and install it parallel with the ground, in ‘horizontally polarized’ configuration, and point it at the crest of the hill that is in the way. This can be done to an equal effect using a vertically polarized yagi, or even using a slim jim that has a narrow take off angle or compressed pattern–hence additional gain. The signal will diffract at the ridge line, and may or may not bend enough to get the signal to the receiver. The signal will not be heard on the opposite side at the base of the hill or obstacle, but can be heard further away from the diffraction point.
A five element yagi has at least 7dBi of gain at practical heights, and will boost the 0.5 watt signal to an estimated radiated power (ERP) of almost 1.5 watts, if the cable is shorter, and if connections are not too ‘lossy’. If the transmitting antenna is horizontally polarized to maximize the range through thick forests, and to diffract over obstacles in it’s radio line of sight, and to reduce detection, then the receiving antenna must also be horizontally polarized.
