[K2] External amplifier keying circuit question
Locked
[K2] External amplifier keying circuit question
 
|
I'm planning to add an external amplifier/transverter keying circuit to one of my K2s. I found two versions on the web, both apparently designed by N0SS (SK). The one on the Elecraft site (http://www.elecraft.com/Apps/Amp_keying_ckt.htm ) appears to be his original circuit, using a 2N7000 driving a 2N2222. The archive of Tom's later kit offering (http://www.mmccs.com/mmarc/n0ss/k2_t-r_rly_drvr.pdf ) uses two MOSFETs and is capable of keying somewhat higher voltage and current. But also he added a 100k resistor from the input gate (8R) to ground and another from the gate of the second MOSFET to ground.
I am trying to figure out if these two 100 k resistors serve any useful purpose or if I can happily leave them both out of the 2-MOSFET circuit. There doesn't immediately appear to be any need to pull these gates down as there are several loads on the input 8R voltage (on the K2 RF board) which will do that for the 1st MOSFET, and the 1st MOSFET will pull down the gate of the 2nd one when needed. Maybe something odd will happen on power-up or power-down? Any thoughts? 73,Steve VE3SMA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
Re: [K2] External amplifier keying circuit question
|
|
Steve,
It is not a good idea to leave the gate of a MOSFET with no static drain on it. When the board is removed from the K2 the gate at the input is exposed - thus the 100k The 100k between the 2 devices might be omitted if you wish. The first link you mentioned is Eric Swartz work - the second is from Tom Hammond (SK). I would recommend Tom's version. The 2nd FET could be a 2N7000 if it will handle the current and voltage that you have to deal with. 73, Don W3FPR On 5/16/2016 10:01 AM, Steve Kavanagh via Elecraft wrote: > I'm planning to add an external amplifier/transverter keying circuit to one of my K2s. I found two versions on the web, both apparently designed by N0SS (SK). The one on the Elecraft site (http://www.elecraft.com/Apps/Amp_keying_ckt.htm ) appears to be his original circuit, using a 2N7000 driving a 2N2222. The archive of Tom's later kit offering (http://www.mmccs.com/mmarc/n0ss/k2_t-r_rly_drvr.pdf ) uses two MOSFETs and is capable of keying somewhat higher voltage and current. But also he added a 100k resistor from the input gate (8R) to ground and another from the gate of the second MOSFET to ground. > I am trying to figure out if these two 100 k resistors serve any useful purpose or if I can happily leave them both out of the 2-MOSFET circuit. There doesn't immediately appear to be any need to pull these gates down as there are several loads on the input 8R voltage (on the K2 RF board) which will do that for the 1st MOSFET, and the 1st MOSFET will pull down the gate of the 2nd one when needed. Maybe something odd will happen on power-up or power-down? > Any thoughts? > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
|
|
In reply to this post by Elecraft mailing list
I did a bit of a write-up when I added the keying circuit to my K2 (based on the article on the Elecraft website), hopefully you find it useful:http://www.mwrs.org.au/2014/04/20/elecraft-k2-amplifier-keying-circuit/
73, Matt VK2RQ On Mon, May 16, 2016 at 7:03 AM -0700, "Steve Kavanagh via Elecraft" <[hidden email]> wrote: I'm planning to add an external amplifier/transverter keying circuit to one of my K2s. I found two versions on the web, both apparently designed by N0SS (SK). The one on the Elecraft site (http://www.elecraft.com/Apps/Amp_keying_ckt.htm ) appears to be his original circuit, using a 2N7000 driving a 2N2222. The archive of Tom's later kit offering (http://www.mmccs.com/mmarc/n0ss/k2_t-r_rly_drvr.pdf ) uses two MOSFETs and is capable of keying somewhat higher voltage and current. But also he added a 100k resistor from the input gate (8R) to ground and another from the gate of the second MOSFET to ground. I am trying to figure out if these two 100 k resistors serve any useful purpose or if I can happily leave them both out of the 2-MOSFET circuit. There doesn't immediately appear to be any need to pull these gates down as there are several loads on the input 8R voltage (on the K2 RF board) which will do that for the 1st MOSFET, and the 1st MOSFET will pull down the gate of the 2nd one when needed. Maybe something odd will happen on power-up or power-down? Any thoughts? 73,Steve VE3SMA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
Re: [K2] External amplifier keying circuit question
|
|
In reply to this post by Elecraft mailing list
Thanks, Don. Good point re the input side...I guess I'm not used to having plug-in boards in mind!
Yes, I was thinking of a pair of 2N7000s - they are fine for the current and voltage I need to switch. 73, Steve VE3SMA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
Re: [K2] External amplifier keying circuit question
|
|
In reply to this post by Elecraft mailing list
Initial testing using the two-MOSFET circuit (http://www.mmccs.com/mmarc/n0ss/k2_t-r_rly_drvr.pdf ) with two 2N7000s, but with R3 removed, indicates that it is working fine, switching a load of about 50 mA at 12-13V. I left R2 in.
Thanks all for your comments. 73, Steve VE3SMA ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email] |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |