Antenna sharing with transceiver, what I am doing
Posted: Wed Jan 10, 2018 11:24 pm
Consider this still a bit "experimental" but I think I'm on the road to success, and thought I'd share
In another thread, I explained how I'm wanting to use the RSP2pro as a diagnostic tool for signal strength evaluation. That hasn't changed.
But I also want to use it as a panadapter for my HF rig.
Here's what I've got going right now. The rig is an ICOM IC-7200 and AL-811 amp. I've been playing with a receiver, an ICOM IC-75, sharing the same antenna as the IC-7200. Results have been ok using the MFJ-1708 antenna switch. More on the MFJ 1708 later.
Timing is everything, and the IC-R75 has a "mute" function with kills the front end of the radio. Basically, it shuts off the +5vDC power going to the front end. That, along with the MFJ-1708 has given great results, but .... I've been thinking about the RSP2pro and its lack of a mute function.
So here's my simple work around, and remember - timing is everything.
Instead of letting the IC-7200 key the MFJ-1708, I have completed a little relay box, to pre-trigger the MFJ-1708.
What I did was build a small box with two relays in it. There are corresponding ICOM mic jacks on the box (about $6.00 each). There are input and output RCA jacks on the box (10 for $7.95 on Amazon). I built up a short "jumper" to go from the box to the IC-7200, which used a bit of HeilWire and two ICOM mic plugs (maybe $10 total). There is also a 12v barrel jack ($1.50) on the box. Inside the relay box are two 12vDC DPDT relays.
Here's how it works. I plug the ICOM mic into the "box" and tap into its PTT line. That line is routed inside the box the coil of one of the relays. The NO contacts of the relay are wired to trigger the MFJ-1708. The remaining set of contacts on that relay energize the coil on the second relay. That relay's NO contacts are used to key up the IC-7200. In that manner... the second relay is acting as a time delay, while the first relay triggers the MFJ-1708. Its a bit of insurance, and cheap, and easy to do. My mic does not use the +8vDC supplied by the IC-7200, so I've got a capacitor to block the DC and allow the AC of the mic through. I used a Sprague Orange Drop, .01uF @ 600v, but that's because I had one handy! Any old ceramic or silver mica or polyfilm capacitor of similar value should do. Err on the large capacitance if need be.
In operation, the mic triggers relay #1, which does two things. First it triggers the MFJ antenna switch, and also triggers relay #2. Relay #2 gets the radio into transmit mode. I've got enough time delay built in, to give it "insurance" upon pressing PTT
But wait... how about when you release PTT?
No problem! The MFJ-1708 provides a 0-2 second time delay to switch back to "recieve mode". So, just set the delay to something reasonable to assure the PTT is off, the radio has stopped transmitting, and your amp is off, before allowing the transfer of the antenna back to receive mode.
So we've got a bit of extra time delay on xmit, and a bit on recv too.
This all has worked exceptionally well on the IC-R75. I'll know in a day or two about the RSP2pro.
A little insight to the MFJ-1708. There are two models, the 1708 and the 1708SDR
The "SDR" model has a jumper that shorts the incoming from the transceiver to the antenna. This is to allow the transceiver to "receive" even as the SDR is acting as a panadapter. There is a 3db loss in so doing, not a huge deal for receive. If you get the regular "1708" you can install the jumper yourself. Again, no big deal. The "SDR" model also nixes the regularly unused switching port that the normal model 1708 has. They both list for $79.95 and more my money, I got the normal model, as I don't need a jumper. But if you do, just add it and keep the switching port.
As extra-extra insurance, I put two 6amp diodes between the receive antenna port's center and ground. Should something unthinkable happen, those diodes will give a little bit of extra protection to the receiver.
Well that's about it.
This is long, but hope it can help someone.
Charlie B, K1VCT
In another thread, I explained how I'm wanting to use the RSP2pro as a diagnostic tool for signal strength evaluation. That hasn't changed.
But I also want to use it as a panadapter for my HF rig.
Here's what I've got going right now. The rig is an ICOM IC-7200 and AL-811 amp. I've been playing with a receiver, an ICOM IC-75, sharing the same antenna as the IC-7200. Results have been ok using the MFJ-1708 antenna switch. More on the MFJ 1708 later.
Timing is everything, and the IC-R75 has a "mute" function with kills the front end of the radio. Basically, it shuts off the +5vDC power going to the front end. That, along with the MFJ-1708 has given great results, but .... I've been thinking about the RSP2pro and its lack of a mute function.
So here's my simple work around, and remember - timing is everything.
Instead of letting the IC-7200 key the MFJ-1708, I have completed a little relay box, to pre-trigger the MFJ-1708.
What I did was build a small box with two relays in it. There are corresponding ICOM mic jacks on the box (about $6.00 each). There are input and output RCA jacks on the box (10 for $7.95 on Amazon). I built up a short "jumper" to go from the box to the IC-7200, which used a bit of HeilWire and two ICOM mic plugs (maybe $10 total). There is also a 12v barrel jack ($1.50) on the box. Inside the relay box are two 12vDC DPDT relays.
Here's how it works. I plug the ICOM mic into the "box" and tap into its PTT line. That line is routed inside the box the coil of one of the relays. The NO contacts of the relay are wired to trigger the MFJ-1708. The remaining set of contacts on that relay energize the coil on the second relay. That relay's NO contacts are used to key up the IC-7200. In that manner... the second relay is acting as a time delay, while the first relay triggers the MFJ-1708. Its a bit of insurance, and cheap, and easy to do. My mic does not use the +8vDC supplied by the IC-7200, so I've got a capacitor to block the DC and allow the AC of the mic through. I used a Sprague Orange Drop, .01uF @ 600v, but that's because I had one handy! Any old ceramic or silver mica or polyfilm capacitor of similar value should do. Err on the large capacitance if need be.
In operation, the mic triggers relay #1, which does two things. First it triggers the MFJ antenna switch, and also triggers relay #2. Relay #2 gets the radio into transmit mode. I've got enough time delay built in, to give it "insurance" upon pressing PTT
But wait... how about when you release PTT?
No problem! The MFJ-1708 provides a 0-2 second time delay to switch back to "recieve mode". So, just set the delay to something reasonable to assure the PTT is off, the radio has stopped transmitting, and your amp is off, before allowing the transfer of the antenna back to receive mode.
So we've got a bit of extra time delay on xmit, and a bit on recv too.
This all has worked exceptionally well on the IC-R75. I'll know in a day or two about the RSP2pro.
A little insight to the MFJ-1708. There are two models, the 1708 and the 1708SDR
The "SDR" model has a jumper that shorts the incoming from the transceiver to the antenna. This is to allow the transceiver to "receive" even as the SDR is acting as a panadapter. There is a 3db loss in so doing, not a huge deal for receive. If you get the regular "1708" you can install the jumper yourself. Again, no big deal. The "SDR" model also nixes the regularly unused switching port that the normal model 1708 has. They both list for $79.95 and more my money, I got the normal model, as I don't need a jumper. But if you do, just add it and keep the switching port.
As extra-extra insurance, I put two 6amp diodes between the receive antenna port's center and ground. Should something unthinkable happen, those diodes will give a little bit of extra protection to the receiver.
Well that's about it.
This is long, but hope it can help someone.
Charlie B, K1VCT