[Elecraft] KPA500 question (long answer)
Don Wilhelm
w3fpr at embarqmail.com
Wed Jun 15 23:06:37 EDT 2011
Joe, Jack,
Actually, the situation get more complicated. A lot of the "problem"
goes back to the time Elecraft added pullup resistors to the K3 band
data outputs because many users did not understand what pullup resistors
are, nor what they accomplished.
Now with the advent of the KPA500, this situation has re-surfaced, and
it is causing problems with band decoders used with the K3 and KPA500.
The situation can be cured with isolation diodes and pullup resistors in
the external device using the band decoder outputs of the K3.
To start, let me try to provide information about what a pullup resistor
is. This is common in the world of logic circuits, and is admittedly
not thought about much in analog circles, although the same thing applies.
Any logic signal line has a driver, and if that signal is to be
recognized, there must be a receiver on the other end of the signalling
line.
At the driver end, you have a transistor (or FET) that is either
conducting or not conducting. The conducting state (low state) can
easily be sensed on the other end of the line by zero ohms (or zero
volts) at the receiving end. However, the non-conducting state of the
driving transistor/FET is not so easily determined in some cases.
If the driving device has an open collector/drain driver, then when the
driver is not conducting (high state), it will appear as an open circuit.
Now skip to the receiving end. The receiver can easily detect the low
level (zero volts) state because it responds to voltage on the signal
line. But what about the high state - there is no source of voltage on
the signal line (yet), there is only a zero volts low state or an open
circuit. The receiving device may not like the open circuit situation,
since its input might detect either a high or a low level because of
noise pickup on the signaling line. There must be something on the
signaling line to produce a high level (greater than the switching level
of the receiving device). That is the function of the pullup resistor -
it "pulls" that open circuit signal line up to a high logic level - a
resistor to a source of voltage will do the job nicely. It is nothing
more than a resistor connected between the signal line and a source of
voltage. The rating of that resistor must be such that the current when
the driver is conducting does not exceed its current rating, and the
voltage that the resistor is connected to must not exceed the voltage
rating of any device that is connected to the signal line.
Ideally, that pullup resistor would be at the most distant receiver on
the signal line, and the voltage that the pullup connects to will be
tolerated by all devices connected to that line.
Now consider the KPA500 and the K3 band data outputs. The KPA500 has
included protection diodes because there are devices that "listen" to
the K3 band data lines and have pullup resistors to +12 volts - the
diodes protect the KPA500 from being damaged by that high voltage.
Consider also, that at the urging of many who were not familiar with the
concept of pullup resistors, the K3 design team conceded and included
pullup resistors in the K3.
Enter the KPA500 plus a non-Elecraft band decoder box - the voltages
present and the signals may "fight". The KPA500 includes isolation
diodes to protect its inputs from excessive voltages that may be applied
by external band decoders. But at the same time, some external band
decoders may load down the signal levels from the K3 band decoder outputs.
If that is your situation, the solution to this problem is to install
isolation diodes in the external band decoder (cathodes toward the K3).
But that solution blocks the +volts from the pullup resistors in the K3
- we are back to square one where pullups are again required in the
receiving device.
If the external band decoder does not already contain pullup resistors,
the isolation diodes will prevent current from the K3 pullup resistors
(with the K3 drivers in the high (open circuit) state from flowing out
to the external decoder and establishing a high state at the receiver.
The only solution to this situation is to add pullup resistors to the
external decoder, so a high state on the signaling line can be
recognized. If the pullup resistors are not installed the receiving
device may interpret a high state incorrectly and produce "garbage"
output. In the logic world, we never want to leave a logic input
"floating" because it is subject to noise and the output of the device
becomes unreliable.
I hope I have not confused, but this is the best way I can describe the
"state of things" - for those familiar with logic signals, you should
easily understand, but I have provided the "long explanation" for those
who are more analog oriented.
73,
Don W3FPR
On 6/15/2011 7:08 PM, Jack Brindle wrote:
> Let me restate this. The diode needs to "point" at the K3 in order for
> the K3 to pull the BCD signal low.
> So the bar (cathode) is towards the K3, while the triangle (anode) is
> connected to the bandswitch.
>
> Looks like I got the two terms backwards in my earlier email.
>
> Jack Brindle, W6FB
>
> On Jun 15, 2011, at 3:39 PM, Joe Subich, W4TV wrote:
>
>>> Anodes towards K3/KPA500 signal junction. Just one diode needed per
>>> BCD signal.
>> No, that will not work since anode to K3/KPA500 will not allow the K3
>> to pull the RCS-12 inputs low. Since I don't have a schematic for the
>> RCS-12 (none published as far as I can fine), my assumption is that
>> the RC-12 has pull-ups on its BCD input.
>>
>> I suppose Dave could measure the voltage on pins 1,2,8& 9 of the
>> RCS-12 "Radio Input" jack. That would give some hint as to the
>> circuit design. (I don't know why I'm trying to debug MFJ stuff -
>> just get a real band decoder<G>).
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 6/15/2011 6:18 PM, Jack Brindle wrote:
>>> Nope. That won't work. The BCD outputs are open drain/collector, so
>>> connecting them in this way will actually do nothing.
>>> Anodes towards K3/KPA500 signal junction. Just one diode needed per
>>> BCD
>>> signal.
>>>
>>> Jack Brindle, W6FB
>>>
>>> On Jun 15, 2011, at 3:06 PM, Joe Subich, W4TV wrote:
>>>
>>>>> What kind of isolation diodes would you suggest?
>>>> Any switching diode (1N4148, etc.) would be fine.
>>>>
>>>>> Any how should they be connected?
>>>> As any set to isolation diodes ... two diodes per data line
>>>> (A,B,C,D)
>>>> cathodes to the K3, anodes to the RCS-12 and KPA-500.
>>>>
>>>> 73,
>>>>
>>>> ... Joe, W4TV
>>>>
>>>>
>>>> On 6/15/2011 12:11 AM, Dave Perry wrote:
>>>>> Joe,
>>>>>
>>>>> Yes, I am using the four pins corresponding to Band 0 through
>>>>> Band 3
>>>>> plus the pin for ground. The RCS-12 works fine connected directly
>>>>> to the
>>>>> ACC port on the K3. It also works fine when the KPA500 is
>>>>> connected via
>>>>> the Y cable. It is just that the KPA500 is not switching bands when
>>>>> connected with the RCS-12. So your suspicion may be correct. What
>>>>> kind
>>>>> of isolation diodes would you suggest? Any how should they be
>>>>> connected?
>>>>>
>>>>> Thank you.
>>>>>
>>>>> Dave, N4QS
>>>>>
>>>>> ----- Original Message ----- From: "Joe Subich, W4TV"<lists at subich.com
>>>>> To:<elecraft at mailman.qth.net>
>>>>> Sent: Tuesday, June 14, 2011 10:43 PM
>>>>> Subject: Re: [Elecraft] KPA500 question
>>>>>
>>>>>
>>>>>> You might try isolation diodes between the antenna switch and/or
>>>>>> KPA and the K3. If the KPA is not band switching with the RCS-12
>>>>>> connected, I would suspect the RCS-12 is loading the band data
>>>>>> lines.
>>>>>>
>>>>>> How are you connecting the RCS-12? Are you using the "Yaesu BCD"
>>>>>> connections?
>>>>>>
>>>>>> 73,
>>>>>>
>>>>>> ... Joe, W4TV
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 6/14/2011 11:24 PM, Dave Perry wrote:
>>>>>>> Gary,
>>>>>>>
>>>>>>> Good suggestion. I removed the cable going to the antenna
>>>>>>> switch and
>>>>>>> now the K3 and KPA500 appear to talk to one another when changing
>>>>>>> bands. Pushing a band button on the amp changes the amp and the
>>>>>>> K3 to
>>>>>>> the new band. I still cannot get the two power levels to work.
>>>>>>> I also
>>>>>>> need to figure out how to get the band switch working with the Y
>>>>>>> cable.
>>>>>>>
>>>>>>> Dave, N4QS
>>>>>>> ----- Original Message -----
>>>>>>> From: Gary Gregory
>>>>>>> To: Dave Perry
>>>>>>> Sent: Tuesday, June 14, 2011 10:12 PM
>>>>>>> Subject: Re: [Elecraft] KPA500 question
>>>>>>>
>>>>>>>
>>>>>>> What bothers me is the amp was not switching bands you
>>>>>>> said?...If the
>>>>>>> OPER switch is set then the aux cable should allow you to switch
>>>>>>> bands either way and the amp should indeed switch bands and
>>>>>>> indicate
>>>>>>> that on the LCD.
>>>>>>>
>>>>>>>
>>>>>>> Unfortunately, my FT unit has the original I/O board so I can't
>>>>>>> verify this for you...sorry
>>>>>>>
>>>>>>>
>>>>>>> remove the antenna switch and try see if that makes any
>>>>>>> difference.
>>>>>>>
>>>>>>>
>>>>>>> Gary
>>>>>>>
>>>>>>>
>>>>>>> On 15 June 2011 13:02, Dave Perry<n4qs at comcast.net> wrote:
>>>>>>>
>>>>>>> Gary,
>>>>>>>
>>>>>>> No, I did not remove any pins on the cable. This is the one
>>>>>>> supplied
>>>>>>> by Elecraft and I figured that it would be good to go. I just
>>>>>>> checked
>>>>>>> the cable and five pins have been removed. I just removed the Aux
>>>>>>> Cable from the back of the KPA500 and now the band buttons work
>>>>>>> on
>>>>>>> the amp. So it does appear that the Aux Cable is the culprit.
>>>>>>>
>>>>>>> Dave
>>>>>>> ----- Original Message -----
>>>>>>> From: Gary Gregory
>>>>>>> To: Dave Perry
>>>>>>> Sent: Tuesday, June 14, 2011 9:49 PM
>>>>>>> Subject: Re: [Elecraft] KPA500 question
>>>>>>>
>>>>>>>
>>>>>>> Do you have PIN 10 removed on the KPA-500 end of the Y cable?
>>>>>>>
>>>>>>>
>>>>>>> Gary
>>>>>>>
>>>>>>>
>>>>>>> On 15 June 2011 12:33, Dave Perry<n4qs at comcast.net> wrote:
>>>>>>>
>>>>>>> My KPA500 sn 70 arrived tonight (factory assembled). It took
>>>>>>> just a
>>>>>>> few minutes to hook up and get it on the air. I am using the Y
>>>>>>> cable
>>>>>>> on the ACC port to split off two cables from the K3 ACC port --
>>>>>>> one
>>>>>>> goes to a new RCS-12 Automatic Antenna Switch and the other
>>>>>>> goes to
>>>>>>> the KPA500.
>>>>>>>
>>>>>>> I have AUX BUS on the KPA500 menu turned on and Band Change set
>>>>>>> to
>>>>>>> normal. If I press a band button on the amp, the K3 changes
>>>>>>> bands and
>>>>>>> so does the new antenna switch -- pretty neat. But the band
>>>>>>> display
>>>>>>> on the KPA does not change. I have to hit the key and transmit
>>>>>>> to get
>>>>>>> the band to change on the KPA500. This does not seem correct. It
>>>>>>> would seem that pressing any on the band buttons on the amp
>>>>>>> should
>>>>>>> change the band on the amp and the frequency display as well.
>>>>>>>
>>>>>>> Likewise if I change bands on the K3 or via my logging
>>>>>>> software, the
>>>>>>> K3 and antenna switch change bands, but the KPA500 does not. I
>>>>>>> have
>>>>>>> to tap the paddle and transmit to get the KPA500 to change to the
>>>>>>> correct band. I am wondering if there is a problem with the Aux
>>>>>>> Cable. Any other suggestions?
>>>>>>>
>>>>>>> I am up to date on firmware for both the K3 and KPA500.
>>>>>>>
>>>>>>> The amp runs very quiet and is silky smooth in full QSK mode. I
>>>>>>> just
>>>>>>> need to get the band changing issue resolved. Any help would be
>>>>>>> appreciated.
>>>>>>>
>>>>>>> Thank you.
>>>>>>>
>>>>>>> Dave, N4QS
>>>>>>> ______________________________________________________________
>>>>>>> Elecraft mailing list
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> VK4FD - Motorhome Mobile
>>>>>>> Elecraft Equipment
>>>>>>> K3 #679, KPA-500 #018
>>>>>>> Living the dream!!!
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>>
>>>>>>> VK4FD - Motorhome Mobile
>>>>>>> Elecraft Equipment
>>>>>>> K3 #679, KPA-500 #018
>>>>>>> Living the dream!!!
>>>>>>>
>>>>>>> ______________________________________________________________
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