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K3 with a Kenwood TL-922A

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Chris W7CTH

K3 with a Kenwood TL-922A

I am buying a Kenwood TL-922A Amp. Anything I need to know before I hook the K3 up to it.

Thanks
Chris W7CTH
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Joe Subich, W4TV-4

Re: 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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
>

P.B. Christensen

Re: K3 with a Kenwood TL-922A

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" <[hidden email]>
To: <[hidden email]>
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
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Vic Rosenthal

Re: K3 with a Kenwood TL-922A

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"<[hidden email]>
> To:<[hidden email]>
> 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/
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Fred Townsend

Re: K3 with a Kenwood TL-922A

Please see comments below.

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Vic K2VCO
Sent: Saturday, September 03, 2011 11:51 AM
To: [hidden email]
Subject: Re: [Elecraft] K3 with a Kenwood TL-922A

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.

Vic: Do you realize that placing a diode across the T/R relay slows it down?
If you are going to quickly swing the relay you are better off to shunt the
key line with a transient absorbing device like a transorb. As the name
infers that's a zener that especially designed to absorb transients. That
will speed the decay of the relay field rather than delaying it. The type
transorb used must be selected to have a sustaining voltage greater than
normal key line voltage. You want the transorb to only conduct during the
transient period.

73
de Fred, AE6QL

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Joe Subich, W4TV-4

Re: K3 with a Kenwood TL-922A

> Vic: Do you realize that placing a diode across the T/R relay slows
> it down?

The diode only slows down the release ... the problem is the make time
not the release time.

73,

... Joe, W4TV

On 9/3/2011 3:38 PM, Fred Townsend wrote:

> Please see comments below.
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Vic K2VCO
> Sent: Saturday, September 03, 2011 11:51 AM
> To: [hidden email]
> Subject: Re: [Elecraft] K3 with a Kenwood TL-922A
>
> 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.
>
> Vic: Do you realize that placing a diode across the T/R relay slows it down?
> If you are going to quickly swing the relay you are better off to shunt the
> key line with a transient absorbing device like a transorb. As the name
> infers that's a zener that especially designed to absorb transients. That
> will speed the decay of the relay field rather than delaying it. The type
> transorb used must be selected to have a sustaining voltage greater than
> normal key line voltage. You want the transorb to only conduct during the
> transient period.
>
> 73
> de Fred, AE6QL
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Vic Rosenthal

Re: K3 with a Kenwood TL-922A

In reply to this post by Fred Townsend

The big relay in the TL-922 is too slow, with or without a diode.

On 9/3/2011 12:38 PM, Fred Townsend wrote:

Fred Townsend

Re: K3 with a Kenwood TL-922A

In reply to this post by Joe Subich, W4TV-4

Granted. The point is where time is involved do not suppress the transient
by placing a diode across the relay coil. That doesn't necessarily solve the
problem. You may need to bypass slow mechanical devices with fast electronic
devices like optical isolators for break-in operation.
73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Joe Subich, W4TV
Sent: Saturday, September 03, 2011 1:18 PM
To: [hidden email]
Subject: Re: [Elecraft] K3 with a Kenwood TL-922A

> Vic: Do you realize that placing a diode across the T/R relay slows > it
down?

The diode only slows down the release ... the problem is the make time not
the release time.

73,

... Joe, W4TV

On 9/3/2011 3:38 PM, Fred Townsend wrote:

problem.
>
> Vic: Do you realize that placing a diode across the T/R relay slows it
down?

> If you are going to quickly swing the relay you are better off to
> shunt the key line with a transient absorbing device like a transorb.
> As the name infers that's a zener that especially designed to absorb
> transients. That will speed the decay of the relay field rather than
> delaying it. The type transorb used must be selected to have a
> sustaining voltage greater than normal key line voltage. You want the
> transorb to only conduct during the transient period.
>
> 73
> de Fred, AE6QL
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html
>

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P.B. Christensen

Re: K3 with a Kenwood TL-922A

In reply to this post by Vic Rosenthal

> 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.

Another option to deal with sluggish amp T/R relays involves use of an
external T/R switch like the Ameritron QSK-5, or Array Solutions QSK Master.
Some ops are looking to preserve equipment in its original form, or they're
not comfortable with making the mods, or they're timid about working inside
an amp.

I've been purchasing used QSK-5 units on the used market for under $200,
mostly in good electrical condition. That's a bit more expensive than an
internal mod to the TL 922 amp, but RF switching is fast, silent and
through-loss is reasonably low. I believe a QSK-5PC is also available for
installation inside an amp. It may take some minor changes, but the unit
should apply well to the TL 922. The key line voltage between the amp and
K3 would be more reasonable and a buffer circuit wouldn't be needed.

The only remaining issue when using an external T/R switch is that the first
keyed element in CW is truncated until the PIN diodes take over after the
mechanical frame relay energizes to hold the amp key line low. But, this
too can be solved if one want's to make additional bias/switching mods --
which the QSK-5PC likely includes.

Paul, W9AC

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