Featured: DX Engineering KD9SV Keying Relay (DXE-SV-KR) at DX Engineering.
This is an affiliate link: Hood's Finds may earn a commission from DX Engineering at no extra cost to you. We have not tested this product; the specifics below come from the product listing.
Keying an amplifier looks simple: the radio closes a line, and the amplifier switches to transmit. But the circuit on the amplifier side of that line is not always gentle. Some amplifiers, especially older ones, put high voltage or relay current on their keying line, and a radio's keying output is not always built for that. A keying relay between the two protects the radio. DX Engineering's KD9SV Keying Relay, part DXE-SV-KR, is built for that job.
What the DXE-SV-KR does
DX Engineering says the DXE-SV-KR provides two separate, completely isolated PTT outputs, each capable of handling up to +/- 450VDC at up to 500mA. Its optically isolated PTT input only requires 2mA at 13.8VDC to key. The listing describes it as doing the work of a normally open, ground independent Double Pole Single Throw relay.
According to DX Engineering, it can safely key all DC amplifier relays, including older relays and keying inputs that operate at high voltage (DC, not AC). It is also listed as QSK capable for keying any amplifier that supports high speed CW keying.
Why a radio needs this protection
A modern transceiver's amplifier keying output has its own voltage and current limits, listed in the radio's manual. If the amplifier's keying circuit asks for more than that, the radio's output circuit can be damaged. Because the DXE-SV-KR input is optically isolated and needs very little current, the radio only drives a light load, and the heavier switching happens on the relay's isolated outputs.
Before connecting anything, measure the keying line voltage on the amplifier and compare it with the radio's rating. That one check tells you whether a keying interface is needed.
In a typical setup, the radio's amplifier keying output drives the relay's isolated input, and an isolated output keys the amplifier. Because the outputs are isolated from each other, the second output is available for another device that needs to switch with transmit, as long as it stays within the listed ratings. Check the amplifier's manual to confirm which keying connection it uses.
Setup notes from the listing
- Power: it operates on 13.8VDC to an input 2.1mm DC connector, and a mating plug and wire are included.
- Cables: a transceiver interface cable is not included, and RCA phono patch cables are sold separately.
- Size: it measures 4.375 in. wide, 2.250 in. high and 1.000 in. deep.
- Replacement: DX Engineering says that, except for AC switching, it replaces the Ameritron ARB-704.
One important warning
DX Engineering is explicit: do not connect the DXE-SV-KR to AC voltage relays in antique amplifiers. If an old amplifier switches an AC relay from its keying line, this is not the interface for it.
And a reminder that applies to all amplifier discussions: external linear amplifiers are not legal for use on CB radio. Protecting the radio is part of running any legal amateur station safely.
Where to get it
Check current price and availability: DX Engineering KD9SV Keying Relay (DXE-SV-KR) at DX Engineering.
This is an affiliate link: Hood's Finds may earn a commission from DX Engineering at no extra cost to you. More picks on the gear page.
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