Tempo Ct Tr
Fig. 1. At the receiver location (two-site repeater), a cathode follower feeds the receiver audio into a transformer continuously, but the receiver squelch fceeps audio off the line until a carrier appears. The B+ leg of the two-wire line is held at ground potential by the normally closed COR. When a carrier appears, the ground is moved to the "return" leg and B+ is allowed to flow with the audio through the wire pair. The capacitor on the transformer secondary isolates the dc polarities vsithout disturbing ac faudioj flow.
Fig. 1. At the receiver location (two-site repeater), a cathode follower feeds the receiver audio into a transformer continuously, but the receiver squelch fceeps audio off the line until a carrier appears. The B+ leg of the two-wire line is held at ground potential by the normally closed COR. When a carrier appears, the ground is moved to the "return" leg and B+ is allowed to flow with the audio through the wire pair. The capacitor on the transformer secondary isolates the dc polarities vsithout disturbing ac faudioj flow.
if you don't have to); receive capability can be enhanced by the addition of pre^mps without fear of rf degradation by high field strengths: input/output coverage can be matched to a fare-thee-well, making the range of the receiver equal that of the. transmitter; shielding requirements are minimized or eliminated altogether, simplifying the installation.
One of the secrets of the fantastic 150-mile coverage radius of 73's WA1KG0 repeater is the fact that the receiver and transmitter have been separated by a distance of one-half mile. With the receiver at the top of the mountain determining range, all that was necessary to balance up the system was to adjust the power output of the transmitter to closely match the coverage of the receiver when listening to a 10W mobile unit in a half-quieting area.
Getting the signal from one site to the other can involve secondary "link" setups — subsidiary repeaters operating on a UHF pair. Or it can involve leased telephone lines if the two sites are close enough to justify it economically. As a third alternative - and this is the approach used for the WA1KGO repeater - the two sites can be linked with an overground wire pair strung by the amateur repeater builders themselves. If the facility is on cleared and developed land, then this approach probably will be disallowed by the building owners or land leaseholders. Bui where the terrain between the two sites is high-foliage area, the homebrew wire-stringing might be jusl the right approach.
Even if you can't string wire overground, you might find no objections to under-surface wire-stringing - particularly when the landowner is made to realize that no unsafe voltages or currents are to be transferred over the line. Usually, under-surface wire is only required for esthetic reasons which means you need bury it no deeper than the depth required to conceal the line.
A split-site repeater is no more complex than a single-site system; more often than not, as a matter of fact, it is even simpler. A standard single-contact carrier-operated relay at the receiver can do all the switching necessary to send both audio and dc control signals to the transmitter site. Figures I and 2 show one method for
i control j
Fig. 2. Audio and dc decoupling is accomplished at the transmitter. The dc control voltage is used to trip a sensitive relay (10 mA) with a coil voltage of about 3500fi which keys the push-to-talk circuit. The transformer, with split primary interconnected by a capacitor, passes the audio as the dc is routed at the primary.
i control j
Fig. 2. Audio and dc decoupling is accomplished at the transmitter. The dc control voltage is used to trip a sensitive relay (10 mA) with a coil voltage of about 3500fi which keys the push-to-talk circuit. The transformer, with split primary interconnected by a capacitor, passes the audio as the dc is routed at the primary.
accomplishing this dual function.
At the transmitter site, the audio and control signals are decoupled from the line by another transformer/capacitor arrangement similar to that at the receiver location, and the circuit is complete. There is nothing particularly critical about the impedances of the transformers in either the receiver or the transmitter circuits; this is particularly true where cathode followers are used, due to their wide impedance-matching range. The most important characteristic is the split windings.
Audio anomalies can be remedied by adjusting the isolation capacitor values. The values shown (0.5 ¿iF) were selected for their ability to reject the clicks of dc relay closures. Lowering the value will improve the low-frequency response, but it will increase the likelihood of allowing annoying clicks to be transferred over the line.
Repeater owners sometimes appear reluctant to adopt a wire pair for repeater linking because of some inexplicable fear of hum and audio level problems associated with mixing audio and B+. Such problems are nonexistent, however, in most two-site links. The secret is in the use of "balanced" lines. The. transformers themselves, placed at both terminal points of the line, serve to balance the dc by virtue of the choke action of the windings through which the dc must pass. The only suggestion here would be to use good transformers.
The secret of using only two wires for passing audio and carrier-operated-relay control signals lies in the use of the capacitor-transformer combination, which of course cannot pass dc. The dc is
Fig. 3. Audio conditioning and carrier switching system. The audio transformer impedances are not critical, owing to the wide matehing range of the cathode follower. The split secondary should match the primary of the transmitter-site transformer, however. The 100 kfipot in the cathode follower should be an audio type for smooth setting, though a iinear taper will do the job.
Fig. 3. Audio conditioning and carrier switching system. The audio transformer impedances are not critical, owing to the wide matehing range of the cathode follower. The split secondary should match the primary of the transmitter-site transformer, however. The 100 kfipot in the cathode follower should be an audio type for smooth setting, though a iinear taper will do the job.
Ben Bryant > W8IGQ
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