I have finally set up a Harris RF-350 with the associated KW remote controlled amplifer for use with my receive antenna system.
The DX Engineering Receive Antenna Interface for Transceivers is the unit that made this possible.
The only problem was finding a voltage on the Harris radio that would sink to ground under all circumstances of keying.
The solution was found in the Coupler connection on the back of the radio.
I connected a 10k pullup resistor to pin H which carries 13.8VDC and connected the other end of the resistor to pin B (Coupler Key). This pin goes low on transmit, and could equally well be used to key a small relay if that was desired, but I wanted electronic control of the DX Engineering box. Pin B in turn went to the Transmit Ground connection on the interface.
In addition, I power the interface itself from pin I, which also carries 13.8V.
Works beautifully.
It was very fitting that the first station I worked with the new setup – operating position C – was JA8NFV.
The Harris radio has filters the size of a amateur transceiver, with performance to match, what an incredible pleasure.
Since both the Harris RF-350K transceiver and the Harris 7224 KW LPA (Linear Power Amplifier) have RF Sample outputs, I set up scope monitoring of the system triggered by the CW keying.
Update: After using the Harris in battle I am a bit disappointed. The sequencing leaves a bit to be desired, this will be improved with a DX Engineering sequencer already ordered, and there seems to be a bit of filter blow-by on CW. I am hearing CW signals outside the filter passband. I will test another unit to see if this is a common problem, perhaps a bit of contact cleaner will clear this up. On SSB the Harris radios are unsurpassed.
Further analysis indicates that this problem might be caused by impedance mismatch with the headphones I have been using. With those headphones, volume is at almost maximum settings so this seems likely.
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