ORARI SUMSEL INDONESIA

Offset Attenuator

4 MHz. Offset Fox Hunt Attenuator Ideal for the Fox Hunt Loop and Arrow II Antennas Weighs just 2 1/2 Oz. Size is 1 1/2" by 3 1/2" including the connectors. 3 Volt Lithium Battery CR2032 Battery Life is over 100 Hours. BNC Mounts directly on an HT This could very well be the best Offset Attenuator ever made. It uses a 4 MHz. sine wave instead of a square wave use in most Offset Attenuators. This reduces the interference from pagers and other radio services. All metal case for better shielding. Very Important for using with a null type antenna, such as the Fox Hunt Loop. Instructions: Tune your Receiver 4 MHz. above the DF Frequency. Rotate the knob clockwise to turn on the attenuator & increase the attenuation. Turn off when not in use. It's just that Simple Warning: Transmitting may damage the unit.

An Offset Attenuator for Radio Direction Finding Near the end of a transmitter hunt, when the hunter is within a mile or so of the hidden transmitter, the signal level will often exceed the maximum level that a receiver's signal strength indicator can register. The S-meter is "maxed out" and is useless for indicating changes in signal strength. When this occurs a passive resistor network is often used to knock the signal strength down to a useful level. Using a passive attenuator has two main limitations: The maximum signal attenuation is limited to 80 dB or so. When a signal needs to be attenuated by 80 dB or more, the signal is often strong enough to enter the receiver through its case, bypassing the attenuator and the direction finding antenna. An offset attenuator can overcome both of these limitations by Providing attenuation in excess of 100 dB. Allowing the receiver frequency to be set several megahertz away from the hunt frequency, so that the receiver is not directly affected by the strong signal from the hidden transmitter. The following offset attenuator design has a few additional features not found in most other offset attenuators: A 10-dB resistor network attenuator at the front-end that provides some attenuation on the hunt frequency. A clipper circuit helps prevent damage to your receiver when in close proximity to a strong signal source. Read more... Build An Offset Attenuator Has your club held its first hidden transmitter hunt yet? In recent months, Homing In has thoroughly covered special transmitters, controllers and portable antennas for radio direction finding (RDF). With these items and the two-meter handi-talkies that almost every ham owns nowadays, your club is almost completely equipped to start on-foot foxhunting, sometimes called foxtailing, radio-orienteering or ARDF. But before you're ready to go out and bring home the trophies, you will need one more accessory. The fox's signal at the start of a hunt may tickle your receiver with only a fraction of a microvolt. But when you get in close, it could get pounded with nearly a volt of RF, even if the transmitter is running low power. The S-meter circuit of a typical VHF-FM rig won't help you get bearings at that level. It probably shows full scale at 10 microvolts, giving only about 30 dB range from minimum to maximum. Limited range is good because it's easy to see the meter peaks when you swing a directional antenna, but it's bad because your meter will stay pinned when the signal is strong. An RF attenuator is a device that goes between antenna and receiver to reduce the signal strength down to within the range that the receiver S-meter can handle. Without one, you may think you're close to the fox when you're still far away. You won't be able to get close enough to a camouflaged hidden T to identify it. The amount of attenuation should be adjustable so that you can add just a little when your S-meter first pins, up to a lot as you get within a few feet. Special ARDF receivers used by champion foxhunters have electronic attenuation built in, but ordinary handi-talkies don't. Adding it would require major micro-surgery in the HT. To Solve Leakage, QSY External resistive (sometimes called "passive") attenuators are popular for mobile T-hunts. They have several shielded sections, each with resistors to soak up the RF signal and a switch to put the section into and out of the line. But they are not the answer for on-foot hunts, because handi-talkies and scanners are notorious for poor case shielding. A passive attenuator cuts down the RF voltage into the antenna jack, but strong signals will still penetrate the case and pin the S-meter. A better way to get bearings on nearby foxes with HTs is to convert the strong on-frequency signal into a weaker off-frequency signal. Then you can tune your receiver to the offset signal and measure its strength versus direction, either with a dedicated RDF antenna or the "body shield" maneuver.