[Elecraft] KPA500 TX with second radio SOLVED

[Andy Durbin]

"Chuck keeps providing riddles for behavior that is a bit different than what I 
expected. The original K3 with the KIO3 board exhibits exactly the behavior I 
outlined previously. A K3S or K3 with the KIO3B interface behaves the way Chuck 
describes. A look at the KIO3B schematic reveals why - it has series connected 
diodes in the band pull-ups so that when the main Vcc drops at power-off, the 
band lines are disconnected from the power rail. Thus the pull-ups inside the 
KPA500 take over and it sees the magic  pattern indicating that no band is 
connected."

Perhaps I'm a bit perverse but  that provided some amusement.

73,
Andy, k3wyc
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Re: [Elecraft] KPA500 TX with second radio SOLVED

[Jack Brindle via Elecraft]

Chuck keeps providing riddles for behavior that is a bit different than what I 
expected. The original K3 with the KIO3 board exhibits exactly the behavior I 
outlined previously. A K3S or K3 with the KIO3B interface behaves the way Chuck 
describes. A look at the KIO3B schematic reveals why - it has series connected 
diodes in the band pull-ups so that when the main Vcc drops at power-off, the 
band lines are disconnected from the power rail. Thus the pull-ups inside the 
KPA500 take over and it sees the magic  pattern indicating that no band is 
connected.

His solution to switch the RADIO setting to either SERIAL or ANALOG is the 
correct one.

Thanks, Chuck. Any more riddles?

73,
Jack, W6FB


> On Feb 6, 2021, at 4:29 AM, Chuck Chandler  wrote:
> 
> I can confirm this approach works in practice, however one point is important 
> - 
> 
> If you turn off the K3S, but leave the KPA on, the discharge time will be at 
> least ten minutes.  I didn't bother testing after that. 
> 
> If you turn off the K3S, then turn off the KPA, then turn the KPA back on, it 
> has full functions - OPER, band change, etc.  This takes only a little bit of 
> time.  
> 
> I did not observe a KPA band change to 60M though.
> 
> Thanks Jack for taking the trouble of explaining what is going on.  
> 
> 
> 
> 73 de Chuck, WS1L
> 
> chandler...@gmail.com 
> 
> On Fri, Feb 5, 2021 at 6:57 PM Jack Brindle  > wrote:
> This bothered me a bit, so I took a good look at the source code and did some 
> testing. my results may be interesting.
> 
> Chuck’s description with the K3S Not connected to the KPA are correct. When 
> nothing is connected to the band lines, they are pulled high inside the 
> KPA500. In the two radio modes that rely on BAND inputs, this would be an 
> invalid band () and not allow the amplifier to go into OPER mode. Chuck 
> is correct here in that switching to either analog or serial mode will allow 
> the operation he desires.
> 
> But, there is another choice. When the KPA500 is in one of the BCD modes 
> (RADIO = K3 or BCD), and the band signals indicate a valid band, then the KPA 
> will go into OPER mode and should work properly.
> Now, how can this happen with a K3 or K3S attached? The K3/K3S has resistive 
> pull-ups on the band signals, so the signals are pulled up to Vcc when they 
> are not driven to ground. Vcc is the 5V regulated power bus in the 
> transceiver when it is powered. But when the K3/K3S is powered off, the 5V 
> rail will sink to the 0V level as the capacitors bleed off. That means that 
> the band signals are actually pulled to 0V (ground) a short time after the 
> K3/K3S is powered off. This combination defines a valid band, and if the KPA 
> is set to K3 or BCD modes, the amplifier will actually switch to the 60 meter 
> band. It will also go into OPER mode if you tap the OP button.
> 
> So, the alternative solution is to leave the K3S attached, power it off, wait 
> until the KPA500 switches to 60 meters, then you can switch the KPA into OPER 
> mode, switch the input to the alternate rig, and start operating.
> 
> 73!
> Jack, W6FB
> 
> 
>> On Feb 5, 2021, at 5:12 AM, Chuck Chandler > > wrote:
>> 
>> OK, I've figured out the problem.  I took a step back and realized I am 
>> spoiled by the close integration of the K-Line.  The reason the FT101 can't 
>> key the amp is because, unless the K3S is turned on, the amp won't leave 
>> STANDBY mode.  
>> 
>> Even with the AUX cable disconnected, the amp sits in STANDBY and pushing 
>> the OPER-STBY button doesn't do anything.  I guessed a menu setting might 
>> control this, and setting the KPA Menu item RADIO to ANALOG now allows me to 
>> switch bands and from STANDBY to OPERATE via the KPA front panel buttons 
>> with the K3S turned off.  
>> 
>> A quick test shows 25 watts of tube-generated CW gives 450 watts output.  
>> Looks like I'm in business.  Just need to change the menu item when I switch 
>> radios.  
>> 
>> Many thanks to all for the help!
>> 
>> 73 de Chuck, WS1L
>> 
>> chandler...@gmail.com 
>> 
>> On Fri, Feb 5, 2021 at 7:12 AM Chuck Chandler > > wrote:
>> Just tried it out - AUX cable removed, RF Input cable removed, RCA plug with 
>> clip leads inserted in PA Key.  Shorting the leads does not put KPA in TX.  
>> 
>> 73 de Chuck, WS1L
>> 
>> chandler...@gmail.com 
>> 
>> On Thu, Feb 4, 2021 at 6:54 PM Jack Brindle > > wrote:
>> That is good. If you plug a pig-tail RCA jack into the KPA’s PTT input and 
>> short the wires, does the KPA go into TX mode? If so, the issue is in the 
>> transmitter or the cable you are using.
>> You should do this test with nothing connected to the KPA’s RF input. 
>> 
>> As i noted in my post to the reflector, Fred Cady’s book has some very good 
>> info about this. Now if I can find it 

Re: [Elecraft] KPA500 TX with second radio SOLVED

[Chuck Chandler]

I can confirm this approach works in practice, however one point is
important -

If you turn off the K3S, but leave the KPA on, the discharge time will be
at least ten minutes.  I didn't bother testing after that.

If you turn off the K3S, then turn off the KPA, then turn the KPA back on,
it has full functions - OPER, band change, etc.  This takes only a little
bit of time.

I did not observe a KPA band change to 60M though.

Thanks Jack for taking the trouble of explaining what is going on.



73 de Chuck, WS1L

chandler...@gmail.com


On Fri, Feb 5, 2021 at 6:57 PM Jack Brindle  wrote:

> This bothered me a bit, so I took a good look at the source code and did
> some testing. my results may be interesting.
>
> Chuck’s description with the K3S Not connected to the KPA are correct.
> When nothing is connected to the band lines, they are pulled high inside
> the KPA500. In the two radio modes that rely on BAND inputs, this would be
> an invalid band () and not allow the amplifier to go into OPER mode.
> Chuck is correct here in that switching to either analog or serial mode
> will allow the operation he desires.
>
> But, there is another choice. When the KPA500 is in one of the BCD modes
> (RADIO = K3 or BCD), and the band signals indicate a valid band, then the
> KPA will go into OPER mode and should work properly.
> Now, how can this happen with a K3 or K3S attached? The K3/K3S has
> resistive pull-ups on the band signals, so the signals are pulled up to Vcc
> when they are not driven to ground. Vcc is the 5V regulated power bus in
> the transceiver when it is powered. But when the K3/K3S is powered off, the
> 5V rail will sink to the 0V level as the capacitors bleed off. That means
> that the band signals are actually pulled to 0V (ground) a short time after
> the K3/K3S is powered off. This combination defines a valid band, and if
> the KPA is set to K3 or BCD modes, the amplifier will actually switch to
> the 60 meter band. It will also go into OPER mode if you tap the OP button.
>
> So, the alternative solution is to leave the K3S attached, power it off,
> wait until the KPA500 switches to 60 meters, then you can switch the KPA
> into OPER mode, switch the input to the alternate rig, and start operating.
>
> 73!
> Jack, W6FB
>
>
> On Feb 5, 2021, at 5:12 AM, Chuck Chandler  wrote:
>
> OK, I've figured out the problem.  I took a step back and realized I am
> spoiled by the close integration of the K-Line.  The reason the FT101 can't
> key the amp is because, unless the K3S is turned on, the amp won't leave
> STANDBY mode.
>
> Even with the AUX cable disconnected, the amp sits in STANDBY and pushing
> the OPER-STBY button doesn't do anything.  I guessed a menu setting might
> control this, and setting the KPA Menu item RADIO to ANALOG now allows me
> to switch bands and from STANDBY to OPERATE via the KPA front panel buttons
> with the K3S turned off.
>
> A quick test shows 25 watts of tube-generated CW gives 450 watts output.
> Looks like I'm in business.  Just need to change the menu item when I
> switch radios.
>
> Many thanks to all for the help!
>
> 73 de Chuck, WS1L
>
> chandler...@gmail.com
>
>
> On Fri, Feb 5, 2021 at 7:12 AM Chuck Chandler 
> wrote:
>
>> Just tried it out - AUX cable removed, RF Input cable removed, RCA plug
>> with clip leads inserted in PA Key.  Shorting the leads does not put KPA in
>> TX.
>>
>> 73 de Chuck, WS1L
>>
>> chandler...@gmail.com
>>
>>
>> On Thu, Feb 4, 2021 at 6:54 PM Jack Brindle  wrote:
>>
>>> That is good. If you plug a pig-tail RCA jack into the KPA’s PTT input
>>> and short the wires, does the KPA go into TX mode? If so, the issue is in
>>> the transmitter or the cable you are using.
>>> You should do this test with nothing connected to the KPA’s RF input.
>>>
>>> As i noted in my post to the reflector, Fred Cady’s book has some very
>>> good info about this. Now if I can find it in my electronic copy...
>>>
>>> 73!
>>> Jack, W6FB
>>>
>>>
>>> On Feb 4, 2021, at 3:47 PM, Chuck Chandler 
>>> wrote:
>>>
>>> Hi Jack
>>>
>>> It’s a Yaesu FT101ZD, and my multimeter shows it closes continuity
>>> between the key line center and shield on TX.
>>>
>>> No grid block keying!
>>>
>>> Chuck
>>>
>>> On Thu, Feb 4, 2021 at 18:37 Jack Brindle  wrote:
>>>
 Chuck;

 What is the PTT output from your other radio? It needs to be just
 open-circuit, pull to ground on transmit. If anything else (I’m thinking
 grid-block keying), then I predict a trip back to the factory for your KPA.

 There are two key lines coming into the KPA, and going through the KAT.
 These are the AUX I/O PTT, and the RCA-jack PTT. They are maintained
 separately through the Kat on their way to the KPA. Either can key the
 KPA500, and both are opened by the KAT when it has high SWR or needs to
 tune. The AUX I/O version is only meant be used with Elecraft rigs using 0
 - 5 signaling. The RCA jack is likewise meant to be used with rigs that
 only pull 

Re: [Elecraft] KPA500 TX with second radio SOLVED

[Jack Brindle via Elecraft]

This bothered me a bit, so I took a good look at the source code and did some 
testing. my results may be interesting.

Chuck’s description with the K3S Not connected to the KPA are correct. When 
nothing is connected to the band lines, they are pulled high inside the KPA500. 
In the two radio modes that rely on BAND inputs, this would be an invalid band 
() and not allow the amplifier to go into OPER mode. Chuck is correct here 
in that switching to either analog or serial mode will allow the operation he 
desires.

But, there is another choice. When the KPA500 is in one of the BCD modes (RADIO 
= K3 or BCD), and the band signals indicate a valid band, then the KPA will go 
into OPER mode and should work properly.
Now, how can this happen with a K3 or K3S attached? The K3/K3S has resistive 
pull-ups on the band signals, so the signals are pulled up to Vcc when they are 
not driven to ground. Vcc is the 5V regulated power bus in the transceiver when 
it is powered. But when the K3/K3S is powered off, the 5V rail will sink to the 
0V level as the capacitors bleed off. That means that the band signals are 
actually pulled to 0V (ground) a short time after the K3/K3S is powered off. 
This combination defines a valid band, and if the KPA is set to K3 or BCD 
modes, the amplifier will actually switch to the 60 meter band. It will also go 
into OPER mode if you tap the OP button.

So, the alternative solution is to leave the K3S attached, power it off, wait 
until the KPA500 switches to 60 meters, then you can switch the KPA into OPER 
mode, switch the input to the alternate rig, and start operating.

73!
Jack, W6FB


> On Feb 5, 2021, at 5:12 AM, Chuck Chandler  wrote:
> 
> OK, I've figured out the problem.  I took a step back and realized I am 
> spoiled by the close integration of the K-Line.  The reason the FT101 can't 
> key the amp is because, unless the K3S is turned on, the amp won't leave 
> STANDBY mode.  
> 
> Even with the AUX cable disconnected, the amp sits in STANDBY and pushing the 
> OPER-STBY button doesn't do anything.  I guessed a menu setting might control 
> this, and setting the KPA Menu item RADIO to ANALOG now allows me to switch 
> bands and from STANDBY to OPERATE via the KPA front panel buttons with the 
> K3S turned off.  
> 
> A quick test shows 25 watts of tube-generated CW gives 450 watts output.  
> Looks like I'm in business.  Just need to change the menu item when I switch 
> radios.  
> 
> Many thanks to all for the help!
> 
> 73 de Chuck, WS1L
> 
> chandler...@gmail.com 
> 
> On Fri, Feb 5, 2021 at 7:12 AM Chuck Chandler  > wrote:
> Just tried it out - AUX cable removed, RF Input cable removed, RCA plug with 
> clip leads inserted in PA Key.  Shorting the leads does not put KPA in TX.  
> 
> 73 de Chuck, WS1L
> 
> chandler...@gmail.com 
> 
> On Thu, Feb 4, 2021 at 6:54 PM Jack Brindle  > wrote:
> That is good. If you plug a pig-tail RCA jack into the KPA’s PTT input and 
> short the wires, does the KPA go into TX mode? If so, the issue is in the 
> transmitter or the cable you are using.
> You should do this test with nothing connected to the KPA’s RF input. 
> 
> As i noted in my post to the reflector, Fred Cady’s book has some very good 
> info about this. Now if I can find it in my electronic copy...
> 
> 73!
> Jack, W6FB
> 
> 
>> On Feb 4, 2021, at 3:47 PM, Chuck Chandler > > wrote:
>> 
>> Hi Jack
>> 
>> It’s a Yaesu FT101ZD, and my multimeter shows it closes continuity between 
>> the key line center and shield on TX. 
>> 
>> No grid block keying!
>> 
>> Chuck
>> 
>> On Thu, Feb 4, 2021 at 18:37 Jack Brindle > > wrote:
>> Chuck;
>> 
>> What is the PTT output from your other radio? It needs to be just 
>> open-circuit, pull to ground on transmit. If anything else (I’m thinking 
>> grid-block keying), then I predict a trip back to the factory for your KPA.
>> 
>> There are two key lines coming into the KPA, and going through the KAT. 
>> These are the AUX I/O PTT, and the RCA-jack PTT. They are maintained 
>> separately through the Kat on their way to the KPA. Either can key the 
>> KPA500, and both are opened by the KAT when it has high SWR or needs to 
>> tune. The AUX I/O version is only meant be used with Elecraft rigs using 0 - 
>> 5 signaling. The RCA jack is likewise meant to be used with rigs that only 
>> pull the signal to ground on transmit, and leave it open on receive.
>> 
>> Thus my question - what i the signal characteristic of the rigs PTT output?
>> 
>> 73!
>> Jack, W6FB
>> Elecraft Engineering
>> 
>> 
>> > On Feb 4, 2021, at 2:15 PM, Chuck Chandler > > > wrote:
>> > 
>> > Just a follow-up to my question about using the KPA500/KAT500 with a
>> > second, older radio.  I just finished some more testing and found that when
>> > I remove the AUX cable 

Re: [Elecraft] KPA500 TX with second radio SOLVED

[Chuck Chandler]

OK, I've figured out the problem.  I took a step back and realized I am
spoiled by the close integration of the K-Line.  The reason the FT101 can't
key the amp is because, unless the K3S is turned on, the amp won't leave
STANDBY mode.

Even with the AUX cable disconnected, the amp sits in STANDBY and pushing
the OPER-STBY button doesn't do anything.  I guessed a menu setting might
control this, and setting the KPA Menu item RADIO to ANALOG now allows me
to switch bands and from STANDBY to OPERATE via the KPA front panel buttons
with the K3S turned off.

A quick test shows 25 watts of tube-generated CW gives 450 watts output.
Looks like I'm in business.  Just need to change the menu item when I
switch radios.

Many thanks to all for the help!

73 de Chuck, WS1L

chandler...@gmail.com


On Fri, Feb 5, 2021 at 7:12 AM Chuck Chandler  wrote:

> Just tried it out - AUX cable removed, RF Input cable removed, RCA plug
> with clip leads inserted in PA Key.  Shorting the leads does not put KPA in
> TX.
>
> 73 de Chuck, WS1L
>
> chandler...@gmail.com
>
>
> On Thu, Feb 4, 2021 at 6:54 PM Jack Brindle  wrote:
>
>> That is good. If you plug a pig-tail RCA jack into the KPA’s PTT input
>> and short the wires, does the KPA go into TX mode? If so, the issue is in
>> the transmitter or the cable you are using.
>> You should do this test with nothing connected to the KPA’s RF input.
>>
>> As i noted in my post to the reflector, Fred Cady’s book has some very
>> good info about this. Now if I can find it in my electronic copy...
>>
>> 73!
>> Jack, W6FB
>>
>>
>> On Feb 4, 2021, at 3:47 PM, Chuck Chandler  wrote:
>>
>> Hi Jack
>>
>> It’s a Yaesu FT101ZD, and my multimeter shows it closes continuity
>> between the key line center and shield on TX.
>>
>> No grid block keying!
>>
>> Chuck
>>
>> On Thu, Feb 4, 2021 at 18:37 Jack Brindle  wrote:
>>
>>> Chuck;
>>>
>>> What is the PTT output from your other radio? It needs to be just
>>> open-circuit, pull to ground on transmit. If anything else (I’m thinking
>>> grid-block keying), then I predict a trip back to the factory for your KPA.
>>>
>>> There are two key lines coming into the KPA, and going through the KAT.
>>> These are the AUX I/O PTT, and the RCA-jack PTT. They are maintained
>>> separately through the Kat on their way to the KPA. Either can key the
>>> KPA500, and both are opened by the KAT when it has high SWR or needs to
>>> tune. The AUX I/O version is only meant be used with Elecraft rigs using 0
>>> - 5 signaling. The RCA jack is likewise meant to be used with rigs that
>>> only pull the signal to ground on transmit, and leave it open on receive.
>>>
>>> Thus my question - what i the signal characteristic of the rigs PTT
>>> output?
>>>
>>> 73!
>>> Jack, W6FB
>>> Elecraft Engineering
>>>
>>>
>>> > On Feb 4, 2021, at 2:15 PM, Chuck Chandler 
>>> wrote:
>>> >
>>> > Just a follow-up to my question about using the KPA500/KAT500 with a
>>> > second, older radio.  I just finished some more testing and found that
>>> when
>>> > I remove the AUX cable from the back of the KPA and try to put the KPA
>>> into
>>> > TX with the keyline, it stays in RX.
>>> >
>>> > A continuity tester confirms the rig keyline is closing when the rig
>>> is in
>>> > TX, and the KPA shows driver power output, as does the KAT.  But, the
>>> KPA
>>> > won't switch to TX and amplify.
>>> >
>>> > Is there some other function keeping the KPA in RX even though the AUX
>>> > cable is disconnected?
>>> >
>>> > 73 de Chuck, WS1L
>>> >
>>> > chandler...@gmail.com
>>> > __
>>> > Elecraft mailing list
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>>>
>>> --
>> Sent from Gmail Mobile Chuck Chandler chandler...@gmail.com
>>
>>
>>
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