[Elecraft] K3 key-out jack - configuration needed?

[Oliver "Olli" Dröse]

Hi James,

you don't need to connect an outside pull-up (only if you want to measure 
voltages, so you are basically right as well, depending on what/how you want to 
measure ;-)). The transistor is used as a simple electronic switch here thus 
when getting bias on it's gate it will switch source (connected to ground) 
through to the gate (also groundlevel then, that's why you can simply measure 
for 0 ohm resistance between drain and chassis when keyed). If no bias then 
infinite ohms at drain.

Anyway, thanks for your assistance and advices! This is what I love about 
Elecraft and their email reflector. ;-))

73, Olli - DH8BQA



----- Original Message ----- 
From: "JAMES ROGERS" <w4atk at bellsouth.net>
To: "Oliver "Olli" Dröse" <droese at necg.de>
Sent: Sunday, October 10, 2010 6:29 PM
Subject: Re: [Elecraft] K3 key-out jack - configuration needed?


Oliver, it is a MOSFET, IRF630 and you may be right, but I would not
expect to see any change until I provided a voltage source to the Key
Out line. So, if it was me I would do the "pull up" resistor test I
described earlier just to be on the safe side. It appears from the
schematic that it is switched by the 7R line. K3 schematics, RF Board
sheet 1 of 4. There is no drain voltage applied to the IRF630 so that
will have to be supplied externally.


Jim, W4ATK
On Oct 10, 2010, at 11:05 AM, Oliver Olli Dröse wrote:

> Hi James,
>
> well, resistance check should work to my mind at least when keying
> the radio. Unkeyed it is an open collector as I understood (thus
> infinite) and keyed the keying transistor is switching to ground so
> then I should measure 0 ohm (or nearly 0, the low-power key-out port
> hast 446 ohm keyed).
>
> Anyway, ofcourse tried with the amp before and as that was not keyed
> I pulled everything out to do the measurements. The amp itself as
> well as the cable is okay. As soon as I put the cable connected to
> the amp to ground /chassis of K3) everything's switching as
> expected. It is just that the RCA jack has no keying signal. :-((
>
> 73, Olli - DH8BQA
>
>
>
> ----- Original Message ----- From: "JAMES ROGERS"
> <w4atk at bellsouth.net>
> To: "Oliver Olli Dröse" <droese at necg.de>
> Sent: Sunday, October 10, 2010 5:28 PM
> Subject: Re: [Elecraft] K3 key-out jack - configuration needed?
>
>
> Oliver,
> Key Out is not a set of dry contacts and thus measuring with a VOM
> for resistance would be a bit problematic. You could use a "pull up"
> resistor (2K or so) from the Key Out line to a power supply, say 12V.
> Put your VOM on an appropriate voltage scale to measure the voltage at
> the junction of the pull up resistor and the Key Out line and the
> voltage to go to near 0 when PTT is activated. Or you could just hook
> up you amp and see if it is keyed when PTT is activated. According to
> the book it will handle up to +200VDC at 5A.
>
> Jim, W4ATK
>
> On Oct 10, 2010, at 9:31 AM, Oliver Olli Dröse wrote:
>
>> Hi guys,
>>
>> preparing for the autumn contest season I thought to do some cable
>> work today.
>> Made up a cable to key the amplifier and wanted to use the key-out
>> jack therefor
>> (only need to sink 13,8 V / 60 mA so should work perfectly well).
>> But the amp
>> isn't keying. So I measured the RCA jack and unkeyed I can measure
>> infinite
>> resistance as it should be the case but if I ptt the radio no change
>> on the RCA
>> jack?! Should be around zero then so no keying there.
>>
>> Checked the manual but couldn't find anything related to
>> configuration of that
>> jack, seems it should be always working, right? Any ideas why it is
>> not?
>>
>> Checked the LP key-out on the ACC connector and that is working
>> properly (but
>> not enough for the amp, ofcourse, only measured there for
>> verification the radio
>> is really keying out, hi).
>>
>> Can anybody help?
>>
>> TIA & 73, Olli - DH8BQA
>>
>>
>>
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>
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