[Elecraft] KE7X KX3 Book and Configuring: KX3, K3, KPA500, and KAT500

Wed Apr 23 07:54:06 EDT 2014

I have four transceivers connected up in such a way that I can use all of
them with the KPA500/KAT500 by simply switching the appropriate RF path to
the KPA500 RF Input port.

The setup is as follows:
-- 'Wiper' of four-port coaxial RF switch connects to KPA500 "RF Input" port

-- The four ports of the coaxial RF switch are connected to: K3, KX3, K2,
HPSDR

-- The "TX Enable/Amp Key Lines" from ONLY the KX3, K2, and HPSDR are
simply paralleled via an assortment of RCA "Y" adapters and connected to
the KPA500 "PA Key" port. NOTE: The K3's "KEY OUT" line is *NOT* included
in this parallel connection, and is not used at all.

-- The K3 is connected to the KPA500 via the KPAK3AUX cable

With this arrangement, and ALL transceivers powered 'ON', I can select any
of the four transceivers via the RF coaxial switch, and drive the KPA500
to full output without issue. The usual steps are:
-- Place the KPA500 into STBY

-- Select the desired transceiver via the RF coaxial switch

-- Select the desired band etc., and make sure the power level is adjusted
appropriately to drive the KPA500.

-- Tap the key to send some 'heads-up' RF to the KPA500, and in response,
the KPA500 switches to the appropriate band, and the KAT500 switches to
the appropriate frequency and pulls the settings from memory.

-- Place the KPA500 into OPERATE mode

That's it. I understand that paralleling the "TX Enable/Amp Key Lines"
from all of the transceivers is less than optimal, but for these
particular transceivers, it has worked fine. Since the K3 is the primary
radio in the shack, it always remains on. (I have NOT tried any of this
with the K3 powered down) I have also used this arrangement with all other
transceivers powered OFF except for the K3 and whichever other radio I
want to use. For example, if I want to use the KX3, the K3 and KX3 are
both  powered ON, but the other transceivers can be OFF. The KX3 will
drive the KPA500 to about 175 watts or so, depending upon band.

I've used this arrangement for quite a while without any issues, but I
make no claim that there are not any dangers in doing things this way. If
there are, I haven't discovered them - yet.

73, Dale
WA8SRA

> Jack,
>
> Thanks for the detailed explanation.  So, if the K3 pulls the keyline to
> ground and the STBY/OPER switch is inoperative as a result, then why would
> power cycle on KPA500 change things.  I mean, I assume that the keyline is
> still pulled to ground by the K3.  But, I admit that I am not an
> electronics guy as you others so I do not fully understand all of the
> stuff that goes on in these things.
>
> 73, phil, K7PEH
>
>
> On Apr 22, 2014, at 10:18 PM, Jack Brindle <jackbrindle at me.com> wrote:
>
>> There appears to be some misconceptions in this discussion. First, the
>> information flow from the K3 to the KPA only occurs on the band lines
>> and the key line. Auxbus communications is one-way, from the KPA to the
>> K3. The KPA does not listen on the Auxbus.
>>
>> There is also something else going on that is in play here. When the K3
>> is powered off, the pull-ups on the band lines (and the key line, I
>> believe) continue to work. They continue to pull the lines to Vcc. But
>> with the K3 off, Vcc is now 0 volts. This means that a short time after
>> the K3 powers off the KPA will see all zeros on the band lines, and will
>> switch to 60 meters. After this, RF coming into the KPA will cause it to
>> switch to the appropriate band, and all band switching will occur with
>> incoming RF as long as the band lines do not change.
>>
>> Of course, there is one other signal in play here. The Key line is
>> important since it causes the KPA to switch into transmit. We have seen
>> the K3 pull the Key line to ground at times, which just may be what you
>> are seeing. If the KEY line is active, the KPA will not switch from STBY
>> to OPER. For this to happen the KEY line must be high.
>>
>> The best way to connect two transceivers to the KPA is to use a physical
>> switch to select the transceiver. A five-pole two position switch will
>> do for the band and key lines, plus a coax switch of the RF.
>>
>> In short, you may get things to work with the description from Fred’s
>> book. But if the key line becomes driven low by the “off” transceiver
>> for any reason, you can expect weird things to happen.
>>
>> Jack Brindle, W6FB
>> Elecraft Engineering
>>
>> On Apr 22, 2014, at 5:04 PM, Phil Hystad <phystad at mac.com> wrote:
>>
>>> Don,
>>>
>>> OK, I may be expecting too much.  Actually, I am not sure if I was
>>> expecting as much as I was a little bit surprised by the behavior.  I
>>> didn't think that the KPA500 and KX3 communicated with each other other
>>> than RF and Key line but maybe that was enough of a difference from the
>>> K3.  The K3 of course in my case has the AUX cable connections with the
>>> KPA500 and KAT500.
>>>
>>> It is not a big deal as long as this is the way it is expected to work.
>>>  I was not sure if I had done something wrong or not.
>>>
>>> But, just picked up W1AW/5 MS QRP power with the KX3.  Actually, it was
>>> about 6 watts.
>>>
>>> 73, phil, K7PEH
>>>
>>>
>>> On Apr 22, 2014, at 4:57 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:
>>>
>>>> Phil,
>>>>
>>>> I think you may be expecting too much.
>>>> Consider a parallel - a computer communicating with a printer.  If you
>>>> suddenly switch the printer cable to another computer, would you
>>>> expect the printer to continue printing without any intervention?
>>>>
>>>> The "printer" in this comparison is the KPA500 and the two "computers"
>>>> are the K3 and the KX3.
>>>>
>>>> It is not unreasonable IMHO to expect that a reset of the KPA500 would
>>>> be required.
>>>>
>>>> If the KPA500 were simply an amplifier with no communications
>>>> capability with the driving transceiver, switching from one source of
>>>> RF input to another should proceed without regard to whatever is the
>>>> driving device, but your KPA500 is more than "just an amplifier"
>>>> because it can communicate with the K3 or KX3 driving transceiver.
>>>> Expecting the KPA500 to switch data streams from two different
>>>> transceivers with no intervening reset is not realistic.
>>>>
>>>> 73,
>>>> Don W3FPR
>>>>
>>>> On 4/22/2014 7:41 PM, Phil Hystad wrote:
>>>>> So, is this normal behavior?  I wasn't expecting any kind of comms
>>>>> between the K3 and the KPA500 that affects the STBY/OPER switching.
>>>>> It does seem that a power on/off cycle for the KPA500 is required to
>>>>> enable that switch.
>>>>>
>>>>> Is this designed to work this way or is this a flaw in the design or
>>>>> maybe a missing mini-feature of configuring two different
>>>>> transceivers with the KPA500.  I admit to not scouring all of the
>>>>> documentation yet on the expected functionality of the STBY/OPER
>>>>> switch.
>>>>>
>>>>> 73, phil, K7PEH
>>>>>
>>>>>
>>>>> On Apr 22, 2014, at 4:14 PM, Don Wilhelm <w3fpr at embarqmail.com>
>>>>> wrote:
>>>>>
>>>>>> Phil,
>>>>>>
>>>>>> Let me get this straight - the KPA500 is communicating with the K3,
>>>>>> then you switch to the KX3 and the KPA500 does not talk with the
>>>>>> KX3.
>>>>>>
>>>>>> If that is what is happening, I would expect that to be the case.
>>>>>> The communications with the K3 is not synchronized with the
>>>>>> attempted communications with the KX3, so a reset (power cycle) of
>>>>>> the KPA500 may be required.
>>>>>>
>>>>>> 73,
>>>>>> Don W3FPR
>>>>>>
>>>>>> On 4/22/2014 7:02 PM, Phil Hystad wrote:
>>>>>>> Some follow-up questions:
>>>>>>>
>>>>>>> OK, I have the KX3 and K3 configured with the KPA500 and KAT500.
>>>>>>> Everything seems to work with one little exception.
>>>>>>>
>>>>>>> The exception:
>>>>>>>
>>>>>>>   --- initial conditions, K3 is on and switched to use the KPA500
>>>>>>> and KAT500.  KX3 is off.
>>>>>>>
>>>>>>>   --- using K3 and so on works fine with amp on or with amp in
>>>>>>> standby.
>>>>>>>
>>>>>>>   --- I turn off K3.  Leave KPA500 on but in STBY mode.
>>>>>>>
>>>>>>>   --- Switch coax from K3 to KX3 (1x2 switch).
>>>>>>>
>>>>>>>   --- Turn on KX3.  KPA500 still in STBY mode.
>>>>>>>
>>>>>>>   --- Attempt to switch KPA500 to OPER from STBY but switch does
>>>>>>> not work.  If I power off the
>>>>>>>        KPA500 (front panel switch) and power back on then switch
>>>>>>> works fine.
>>>>>>>
>>>>>>> I have experimented with all kinds of starting initial conditions
>>>>>>> and order of events but whenever
>>>>>>> the KPA500 is left on after using the K3 and then switching to the
>>>>>>> KX3, the switch on the KPA500
>>>>>>> to go from STBY to OPER does not work.  I always have to cycle the
>>>>>>> power from the front panel on/off
>>>>>>> switch.
>>>>>>>
>>>>>>>
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>>>>
>>>
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