[Elecraft] K3 with a Kenwood TL-922A

[Vic K2VCO]

Actually, I believe that the K3's amp keying output could handle the +120v key line of the 
922 with no trouble. My TL922 came with a diode across the t/r relay, by the way.

BUT -- there is a much bigger problem with the TL-922. That is that the relay is very, 
very slow. You would probably have to increase the TX Delay of the K3 to prevent 
hot-switching, and increasing it beyond 12-15 ms messes up your keying. Buffers and 
soft-keys CANNOT fix this problem.

The designers of the 922 realized that this is problem, and they put a little spark gap 
across the relay contacts. They even warn you in the manual that you may hear arcing from 
this device and it is 'normal'!

Don't believe it! Even with semi-QSK or VOX this means that when you go into transmit, you 
are trying to put power into an open circuit for an instant. That little spark gap is all 
that may (and I mean 'may') stand between you and a burned-up bandswitch. Full QSK is far 
worse.

In my opinion, the TL922 MUST be modified with a faster relay, or you must use PTT, or you 
must use a large-ish amount of TX Delay to prevent hot-switching.

I've modified mine to use a reed relay and vacuum relay for t/r switching. These relays, 
properly driven, switch faster than the minimum 8 ms pre-RF delay provided by the K3 so 
they won't hot-switch.

Yes, you have to do a little work, but it's a lot easier than replacing bandswitch wafers 
(if you can find them).

On 9/2/2011 6:53 PM, Paul Christensen wrote:
> For folks not wanting to modify their amps, a solid-state amp buffer can be
> placed between the K3 and TL-922.  I like the Jackson Harbor "Keyall"
> circuit since it can switch up to 500V AC/DC at several amps and it
> optically isolates the K3's switching transistor from the amp.
>
> http://wb9kzy.com/keyall.pdf
>
> The Keyall is sold as a kit through Jackson Harbor Press, although Andy,
> W8CNZ is providing an assembled plug-'n-play device for about USD $25.
>
> Paul, W9AC
>
>
> ----- Original Message -----
> From: "Joe Subich, W4TV"<lists at subich.com>
> To:<elecraft at mailman.qth.net>
> Sent: Friday, September 02, 2011 9:38 PM
> Subject: Re: [Elecraft] K3 with a Kenwood TL-922A
>
>
>>
>>
>>> Anything I need to know before I hook the K3 up to it.
>>
>> Don't do it!  The TL-922 has a high voltage PTT line with *no* current
>> limiting and no reverse EMF diode across the relay coils.  The relay
>> current is rather high and the "spike" when releasing PTT is quite
>> high.  You will need to add a Harbach engineering "soft key" board -
>>    www.harbachelectronics.com/main/page_products_kenwood_tl922a.html -
>> in order to keep from blowing the K3's keying FET and potentially
>> causing other damage to the K3 due to the spike.
>>
>> Even if you add the soft key board, I would recommend adding "back
>> diodes" across the T/R relay coils and adding a series resistor in
>> the relay line to keep the current down and minimize the potential
>> for a spike.
>>
>> 73,
>>
>>     ... Joe, W4TV
>>
>>
>> On 9/2/2011 8:57 PM, Chris Hembree wrote:
>>> I am buying a Kenwood TL-922A Amp. Anything I need to know before I hook
>>> the K3 up to it.
>>>
>>> Thanks
>>> Chris W7CTH


-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/