Keying a Hercules from K2
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I picked up a used TenTec Hercules amp in very good condition. It works fine from my
Omni A and Omni V, but I'm thinking that I would also like to drive it with my K2. I've looked at the drive from the Omni A, and it appears that 10-15 watts will get me within a dB or so of rated power from the Hercules. The Hercules was designed to work with the old Omni A, which generates a pre-delay keying signal (the call it the "T line") that is +12v on transmit, but transitions roughly 10 ms before the Omni transmits. (The Omni 5 also generates this signal, but doesn't take it outside the radio because later TenTec amps key differently.) The Hercules keying input drives the base of a 2N5087 through 1K, so it isn't going to draw much current. The doc on the K2/100 says that the 8R line is high on receive and 0v on transmit. An app note on the website says that this is a "pre-delay" keying signal that transitions roughly 15 ms before the K2 transmits. It looks like all I need is a simple inverter (NPN, collector to the amp keying line, emitter to chassis, K2 drives the base through 1K) from the 8R line to the Hercules keying line. Does this make sense? My rig also includes a KPA, but I don't think I need it. It has a key output to drive power amps, but there is no doc on it. Is it also a pre-delay signal (that is, 10-20 ms before transmit)? What is its logic -- positive to transmit? Jim Brown K9YC _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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It would be possible to do this switching with the K2 Amplifier Keying
Circuit in Elecraft application notes and adding a PNP transistor and a resistor to provide the correct switching. This could be installed external to the K2 possibly at the TenTec Hercules amplifier keying input. We used a similar circuit when constructing VHF/UHF repeaters from surplus two way radios which use a +ve PTT keying circuit. The NPN output transistor in the K2 keying circuit would be connected to the base of the extra PNP transistor via a 4.7K resistor, the emitter of which is connected to the necessary +ve line and the collector goes to your +ve keying line in the amplifier. The method of operation is when the keying output from the K2 goes to ground this biases on the PNP transistor that connects the keying circuit in the TenTec amp to 12V +ve or whatever you use. This transistor provides the isolation between the different voltages of the K2 (6V) and the TenTec (12V) in use in the respective keying circuits. If felt necessary you could add a pull up resistor of say 10K on the K2 keying output, though we never found this necessary and the prototype repeater that used this circuit has been running on a hill top for many years. Regards, Bob, G3VVT K2 #4168 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jim Brown-10
Jim,
>From your description, the inverter you described is almost correct BUT it won't work because there is no voltage available to it. The output from the KPA100 is a HEXFET open 'collector' - which means it makes a path to ground when active (transmit state) and is open during receive. The Amp Keying Circuit that can be added to the base K2 provides an equivalent output even though it is a transistor collector. You must provide a source of base current for the transistor in the added inverter circuit. Likewise the base of the transistor in the Hercules must have a source of current to drive it to the ON (conducting) state. The inverter circuit will need an NPN transistor, 2 resistors, and a voltage source. Connect the base directly to the KPA100 (or K2) amp keying output with a resistor (1K to 10K) to the voltage source, connect the collector to the Hercules input and a resistor (1K to 5K) to the voltage source. Emitter goes to the common connection between the KPA100 and the Hercules. You can use a voltage source from either the Hercules or the K2 whichever is more convenient or use another voltage source altogether as long as it has the common connected to the Hercules/K2 common. The cleanest implementation would be to build the inverter into the Hercules since there is likely more room than in the K2/100. I prefer to see amplifiers that require an 'Low to Transmit' keying input over the '+ to transmit' because they do not depend on an external voltage source - only a contact (or saturated transistor collector) closure to ground. 73, Don W3FPR ----- Original Message ----- > The Hercules was designed to work with the old Omni A, which generates a pre-delay > keying signal (the call it the "T line") that is +12v on transmit, but transitions roughly 10 > ms before the Omni transmits. (The Omni 5 also generates this signal, but doesn't take > it outside the radio because later TenTec amps key differently.) The Hercules keying > input drives the base of a 2N5087 through 1K, so it isn't going to draw much current. > > The doc on the K2/100 says that the 8R line is high on receive and 0v on transmit. An > app note on the website says that this is a "pre-delay" keying signal that transitions > roughly 15 ms before the K2 transmits. > > It looks like all I need is a simple inverter (NPN, collector to the amp keying line, emitter > to chassis, K2 drives the base through 1K) from the 8R line to the Hercules keying line. > Does this make sense? > > My rig also includes a KPA, but I don't think I need it. It has a key output to drive power > amps, but there is no doc on it. Is it also a pre-delay signal (that is, 10-20 ms before > transmit)? What is its logic -- positive to transmit? > > Jim Brown K9YC > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > > _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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