MFJ-1708 Connection Questions

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Ruben_NB4R
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Joined: Thu Jan 10, 2019 11:52 pm

MFJ-1708 Connection Questions

Postby Ruben_NB4R » Wed Jan 16, 2019 4:15 pm

I have an RSP1A and a MFJ-1708B-SDR. I have a connectivity question. I know how to connect the obvious. SDR-REC XCVR and ANT. My confusion is around the AUX and the CTRL connections. I've connected the RSP1A between the Transceiver and the Linear Amplifier. The MFJ instructions State "The CTRL terminal may be used in place of or in addition to the RF sensing circuit by connecting to the output to key a linear amplifier to energize the MFJ-
1708B-SDR." I'm sorry I've read this sentence in every way I can and it doesn't make any sense. Is the CTRL connected to the amp and is used to key the amp? Then the manual states"If a linear is used then connect the AUX output to the jack that keys the transmitter." HUH!? Connect the AUX jack to the jack that keys the transmitter? I read tech manuals every day and it's been a while since I've read stuff the vague. Anyway, someone please streighten me out on how I need to connect the MFJ-1708 up so when I key the transmitter it will actuate the MFJ box AND key the Linear amp? I appreciate your help.

Ruben
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Ruben_NB4R
Posts: 10
Joined: Thu Jan 10, 2019 11:52 pm

Re: MFJ-1708 Connection Questions

Postby Ruben_NB4R » Wed Jan 16, 2019 6:56 pm

OK, I figured it out. Connect a Y adapter to the port that keys the amp on the rear of the transceiver. One jumper to the MFJ-1708 and one to the amp.
Works perfectly.


Ruben
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ON5HB
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Location: Heppen - Belgium
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Re: MFJ-1708 Connection Questions

Postby ON5HB » Wed Jan 16, 2019 7:55 pm

CTRL is the input that you connect to your TX-control of the Tranceiver, the same as you set your amplifier in Tx mode.
The AUX is just a relay that can be used to trigger other devices, it has 2 settings.

See page 4 of the manual, the AUX is set to NO or NC depending on jumper1.

In short, CTRL is the RX/TX control line coming out of the ACC connector of your tranceiver.

With AUX you can trigger the Amplifier to TX-mode or some other device, but it's just a relay contact, there is no current.

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Greetings,

Bas - ON5HB

Ruben_NB4R
Posts: 10
Joined: Thu Jan 10, 2019 11:52 pm

Re: MFJ-1708 Connection Questions

Postby Ruben_NB4R » Wed Jan 16, 2019 10:48 pm

Thank you ON5HB, That's what I thought. I have the wire from the TX GND on the back of the radio to the CTRL on the 1708B. I've read that I can put a Y connector on the TX GND an go to bothe the 1708 and my amplifier. It seems to work well like that.

I would like to figure out how to mute the RSP1A on transmit. I see what you are saying about the AUX just being just that. An auxiliary contact for other uses.

THANKS AGAIN!
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ON5HB
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Re: MFJ-1708 Connection Questions

Postby ON5HB » Thu Jan 17, 2019 1:51 pm

Well to mute the RSP1A on TX is quite simple.
Just use the AUX-relay to disconnect the speaker/line whatever sound output/speakers you use and make it disconnect.
Then the audio is gone.

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Greetings,

Bas - ON5HB

Ruben_NB4R
Posts: 10
Joined: Thu Jan 10, 2019 11:52 pm

Re: MFJ-1708 Connection Questions

Postby Ruben_NB4R » Sat Jan 19, 2019 5:07 pm

Well I guess I was overthinking the problem. Also, in short, the Y connector idea will not work. the amp is looking for ground to key and using a Y connector defeats this. Here is how I have it connnected. I have TX GND on the back of the radio connected to the CTRL terminal on the 1708. I have my AL-80B connected to the AUX with the jumper set to so when the relay energizes it goes to ground keying the amp. I have Omnirig running and VRX set up for my rig (Yaesu FT1000-mp) . Everything is working as advertised. When radio is keyed, SDRuno mutes the sound. That mute function will work great if you don't have any RF coming into your audio section. Thank you for your help ON5HB.

I hope this information can help someone else.

73
Ruben NB4R
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