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Author Topic: HF TX/RX inline switch for 2 hf radios?  (Read 1431 times)
KT0DD
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Posts: 284




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« on: September 11, 2011, 01:40:51 PM »

I miss my OrionII (I had to sell due to hardship)  because of the feature that I could listen to 2 receivers simultaneously, and when I transmitted, it would disengage both receivers. This of course, was a built in circuit.

I now own a FT-950 and TS-480hx that I would like to listen to simultaneously on the same or different bands, but am afraid of blowing up the front end of the 2nd receiver when I key up the rig I want to transmit on, without a way to disengage the second rig.

Does anyone know of an inline automatic antenna switch for hf that would sense rf and switch out the 2nd receivers antenna line when I transmit on the primary rig?

Thank You. Todd - KT0DD

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W5FYI
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Posts: 1046




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« Reply #1 on: September 11, 2011, 07:00:26 PM »

One way it might be done is to make a series resonant line with front-to-back parallel diodes to ground. Using 40-meters for example, from the transmitter to antenna junction hang a 47pF capacitor in series with a 15┬ÁH inductor, the other end of the inductor going to the second receiver. Where the capacitor and inductor are joined, place a diode pair to ground. Now, when the transmitter is not transmitting, the low power signals from the antenna are below the diode conduction voltage, and RF goes through the series trap to feed the second receiver. However, when the transmitter is active, the diodes conduct instantaneously and short out the second receiver's input. The diodes aren't shorting the transmitter power to ground because the 47pF capacitor is acting as a 500 ohm impedance; the bulk of the transmitter's power will be delivered to the antenna as intended.
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AD5X
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Posts: 1437




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« Reply #2 on: September 12, 2011, 06:35:59 AM »

A simple way to do it is to use a high-speed signal relay like the Omron G6A-274P40-DC12 (Mouser 653-G6A-274P40-DC12) which switches in typically 3ms (spec is 5ms) and handle 3-amps.  I've used these relays in several QSK switches (info in various articles on my website at www.ad5x.com).  Put one of these relays in a little Bud box.  Feed the amp-enable output of the opposite radio to this box to enable the relay to switch the antenna to ground when the other transmitter transmits.

The FT-950 has a 15ms minimum amp-enable-to-RF-out delay.  The TS480 has a minimum 10ms amp-enable-to-RF-out delay.  Both well above the 5ms spec'd switching time of the relays.

Phil - AD5X
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