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Author Topic: Ideas for a RF kill relay  (Read 1047 times)
KC9QQM
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Posts: 181




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« on: August 24, 2012, 10:33:38 AM »

I just ordered the SoftRock RX Ensemble II and will be connecting to the aux RF output jack on the back of my Yaesu FT-101e. I am thinking it will have better sensitivity and I like the idea of doing the receive tuning on my computer. With that said I don't want to smoke it when I go to transmit.

While I type this I am thinking I can using the same PTT voltage that keys the xmit relay and built a small box with a relay that shorts out the antenna input to the SoftRock so I don't over load the RF in to the SDR.
Other ideas?

Jeff
KC9QQM
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K8AC
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Posts: 1465




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« Reply #1 on: August 24, 2012, 11:10:04 AM »

I don't own an FT-101E, but took a look at an online manual regarding your question.  I believe you are in error in talking about the RF output jack.  That provides RF output from the driver stage of the transmitter.  There's also an IF output jack for the 3.180 MHz IF signal and that's the one you want to use.  But - there doesn't appear to be a tuning range option on the SoftRock RX Ensemble II that covers 3.180 MHz. 

At any rate, you won't have any problems overloading the SDR front end since you'd just be sampling the IF signal.  If you were using an outside antenna with the SoftRock RX Ensemble II  and were running substantial transmit power, then your concern would be valid.  There are commercial boxes, such as that by KD9SV, that offer front end protection by doing just want you want to do.  The relays in that box are fast enough to support full QSK if necessary.  I use one of those boxes with my Beverage receive antennas for 160M.

73, Floyd - K8AC
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KC9QQM
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Posts: 181




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« Reply #2 on: August 24, 2012, 12:57:19 PM »

The SoftRock Ensemble input is a normal antenna, not an IF input. It covers from 1.8 to 30 mhz. The FT101e has a antenna output that is seperate from the RF output you are refering to.

After looking at the FT101 schematic closer I see that the REC (RCV Ant) connection on the back is disconnected from the SO-239 antenna connector during transmit so I don't below I wil need to do anything other than run a jumper from this connnection to the SoftRock.

Jeff
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K8AC
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Posts: 1465




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« Reply #3 on: August 24, 2012, 05:24:00 PM »

The SoftRock input is anything you want it to be.  It doesn't know the difference between a signal coming from an antenna and one coming from an IF output.  Using the IF output to the SoftRock would allow you to drive panadaptor software with the IF signal. 
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KB3HG
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Posts: 404




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« Reply #4 on: August 24, 2012, 06:57:36 PM »

Now this is going back to the mid 80's....sensitivity, You have the Yeasu FETs  in the receiver boards, I think two of them. A better FET was used. (higher gain) and yes the circuit determines overall real world gain. this made that radio a hotter receiver. This mod was done on a buddy of mine's FT-101EE WB3IVI (SK) by an engineer next door to him. Made a big difference then. But with the advancement of electronics the Softrock may be the way to go. That was one tweaked radio and clean. I know I put in a few mods for him at the time. But that thing would be about 30 + years old now. Wonder who has it now.

Tom Kb3hg
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G4IJE
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Posts: 243




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« Reply #5 on: August 25, 2012, 02:13:23 AM »

Are your sure that "REC (RCV Ant) connection" does what you think it does? Some rigs used to have an extra "receive only" antenna connector for use with a separate receive antenna, like a long wire or a beverage antenna. Obviously this would be an antenna INPUT, not OUTPUT. A much better (and safer) idea is to get a coaxial switch and switch your antenna between the FT-101E and the SoftRock.
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WA3SKN
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« Reply #6 on: August 28, 2012, 10:57:40 AM »

The "signal-to-noise ratio" is determined by the receivers front end... the first RF stage.  Tapping the IF off the radio will not improve this.  There are many possible reasons to take the signal off at the IF, but sensitivity is not one of them!  And you will probably find that the atmospheric noise will be the controlling figure, anyway.  And double check the PTT operation... it may supply a ground and not a voltage when activated.  And there could be a relay with spare contacts available also!  Time to check the schematics!
73s.

-Mike.
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