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[K2] Solutions for K2 Transverter Quirks

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Steve Kavanagh

[K2] Solutions for K2 Transverter Quirks

The K2 makes quite a nice IF rig for VHF transverters, but it has a few quirks, like most rigs. I've put my solutions to two issues up at www.qsl.net/ve3sma/downloads.htm .

First is a sequencer which switches the RF to the transverter to prevent it from transmitting while its internal antenna relay is switching. This deals with the lack of any way to stop the K2 from transmitting on CW when the key is pressed.

The other is a bandpass filter which gets rid of most of the problems due to the high RF sensitivity of the transmit IF output circuitry to RF.

These are not extensive articles, but there should be enough there for knowledgeable hams to ccopy...or get ideas for better approaches.

73,
Steve VE3SMA
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Don Wilhelm-4

Re: [K2] Solutions for K2 Transverter Quirks

Steve,

I did not have success with that link you posted - I got a 404 error.

There is another solution to inhibit CW until a sequencer has completed
and gives a signal back to the K2. It is my article on PTT for CW on my
website www.w3fpr.com. It interrupts the keying unless the "PTT" signal
to the K2 is present (start the sequencer with a footswitch or other
switch external to the K2).

Yes, the K60XV option does not like VHF RF on the coax connected to the
TX jack - it interferes with the K2 power control. A low pass filter
with a cutoff below 50 MHz (and above 28 MHz) cures that problem A low
power in-line low pass filter works fine. The problem does not exist if
the high power BNC output from the K2 is used.

73,
Don W3FPR

On 11/7/2011 6:17 PM, Steve Kavanagh wrote:

> The K2 makes quite a nice IF rig for VHF transverters, but it has a few quirks, like most rigs. I've put my solutions to two issues up at www.qsl.net/ve3sma/downloads.htm .
>
> First is a sequencer which switches the RF to the transverter to prevent it from transmitting while its internal antenna relay is switching. This deals with the lack of any way to stop the K2 from transmitting on CW when the key is pressed.
>
> The other is a bandpass filter which gets rid of most of the problems due to the high RF sensitivity of the transmit IF output circuitry to RF.
>
> These are not extensive articles, but there should be enough there for knowledgeable hams to ccopy...or get ideas for better approaches.
>
> 73,
> Steve VE3SMA
> ______________________________________________________________
> 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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zeke7237

Re: [K2] Solutions for K2 Transverter Quirks

Add an "l" to the url ;) http://www.qsl.net/ve3sma/downloads.html

I used Don's circuit on my low-band K2 (driving one each
50,144,222,432 XV) and an external sequencer in the Jitney .. the last
step of the sequencer enables TX in the K2. Steve's solution does it
in one board and doesn't require any mods to the K2, and it's
relatively easy to isolate 0dBm ..

I also use a filter similar to Steve's .. happened to have one of
Diz's universal low-pass filters
(http://kitsandparts.com/univlpfilter.php) in the kit box and built it
up for 10M and that eliminated a number of weird behaviours on TX ..

de w1rt/john

On Mon, Nov 7, 2011 at 9:34 PM, Don Wilhelm <[hidden email]> wrote:

> Steve,
>
> I did not have success with that link you posted - I got a 404 error.
>
> There is another solution to inhibit CW until a sequencer has completed
> and gives a signal back to the K2. It is my article on PTT for CW on my
> website www.w3fpr.com. It interrupts the keying unless the "PTT" signal
> to the K2 is present (start the sequencer with a footswitch or other
> switch external to the K2).
>
> Yes, the K60XV option does not like VHF RF on the coax connected to the
> TX jack - it interferes with the K2 power control. A low pass filter
> with a cutoff below 50 MHz (and above 28 MHz) cures that problem A low
> power in-line low pass filter works fine. The problem does not exist if
> the high power BNC output from the K2 is used.
>
> 73,
> Don W3FPR
>
> On 11/7/2011 6:17 PM, Steve Kavanagh wrote:
>> The K2 makes quite a nice IF rig for VHF transverters, but it has a few quirks, like most rigs. I've put my solutions to two issues up at www.qsl.net/ve3sma/downloads.htm .
>>
>> First is a sequencer which switches the RF to the transverter to prevent it from transmitting while its internal antenna relay is switching. This deals with the lack of any way to stop the K2 from transmitting on CW when the key is pressed.
>>
>> The other is a bandpass filter which gets rid of most of the problems due to the high RF sensitivity of the transmit IF output circuitry to RF.
>>
>> These are not extensive articles, but there should be enough there for knowledgeable hams to ccopy...or get ideas for better approaches.
>>
>> 73,
>> Steve VE3SMA
>> ______________________________________________________________
>> 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
>

Steve Kavanagh

Re: [K2] Solutions for K2 Transverter Quirks

In reply to this post by Steve Kavanagh

My apologies regarding the link...as W1RT correctly figured out there should be an L at the end of it:

www.qsl.net/ve3sma/downloads.html

I had seen Don's circuit and decided to go a different route...not having to dig into the K2 was a plus for me (and I had a good supply of the Omron G5Y PC-board-mount RF relays).

I had wondered how W1RT dealt with the RF sensitivity of the transverter out line....now I know ! I have been thinking lately a better solution than the filter might be a high isolation buffer amp with 0dB gain (or an attenuator and then a buffer with gain) built into the K2, but I haven't started looking to see where there might be room.

73,
Steve VE3SMA
______________________________________________________________
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

Don Wilhelm-4

Re: [K2] Solutions for K2 Transverter Quirks

Steve,

The answer to your question involves a discussion about how the K2
handles control of the power output level - in all cases, it tries to
measure the actual power output and the microprocessor controls the
drive level early in the transmit chain to achieve the power output
requested by the power knob.

Just as information about what is happening with that "RF Sensitivity"
problem is that *if* some of the VHF/UHF energy appears on the K60XV TX
output. That condition causes the RF detector on the K60XV to produce
an output on the VRFDET line in the K2 (the detector is not frequency
selective - it is just a diode, similar to an RF probe) - the result of
all that is the K2 microprocessor ends up receiving a signal telling it
that there is too much power at the TX output, and the microprocessor
dutifully reduces the power.

The simple low pass filter is just as effective at curing that condition
as a unity gain buffer stage would be.

The ideal solution would be to modify the transverter so that none of
its output frequency energy appears on the input cable, but that is not
realistic in some situations - it all depends on the transverter.

73,
Don W3FPR

On 11/8/2011 8:15 AM, Steve Kavanagh wrote:

> My apologies regarding the link...as W1RT correctly figured out there should be an L at the end of it:
>
> www.qsl.net/ve3sma/downloads.html
>
> I had seen Don's circuit and decided to go a different route...not having to dig into the K2 was a plus for me (and I had a good supply of the Omron G5Y PC-board-mount RF relays).
>
> I had wondered how W1RT dealt with the RF sensitivity of the transverter out line....now I know ! I have been thinking lately a better solution than the filter might be a high isolation buffer amp with 0dB gain (or an attenuator and then a buffer with gain) built into the K2, but I haven't started looking to see where there might be room.
>
> 73,
> Steve VE3SMA
>

Steve Kavanagh

Re: [K2] Solutions for K2 Transverter Quirks

Don:

Thanks for your comments (and since we haven't corresponded in a while....for your ongoing amazing help to all Elecraft owners through the email reflector).

Actually, the issues I have had with the TX IF port have all been while receiving (with another nearby rig transmitting on VHF...or other signal source), so they do not have anything to do with the transmit power itself. The K2 seems to interpret a bit of power showing on the VRFDET line when in receive mode as a dangerous overload condition (as it would be if it appeared on the much less sensitive detector at the 10W antenna jack....and switches the rig (mostly) into transmit.

I suppose a high field strength leakage from a nearby transmitter could indeed affect the transmit power as well....I haven't knowingly observed that.

I have been working on a 10 GHz transverter (modifying a commercial radio) which will have a 21 MHz IF....which got me thinking about having a broadband solution to the RFI problems, so I wouldn't have to use two different filters to avoid the K2 being upset by nearby talkback link transmissions on 2m. I suppose a low pass filter is another option, but it is more difficult to get a sharp cutoff between 28 and 50 MHz than with a bandpass filter. An even better solution would probably be to apply a bias to the detector circuitry in the K60XV, while in receive mode, which prevents it from operating....but I haven't looked into the feasibility of this.

73,
Steve VE3SMA

--- On Tue, 11/8/11, Don Wilhelm <[hidden email]> wrote:

> From: Don Wilhelm <[hidden email]>
> Subject: Re: [Elecraft] [K2] Solutions for K2 Transverter Quirks
> To: "Steve Kavanagh" <[hidden email]>
> Cc: [hidden email]
> Received: Tuesday, November 8, 2011, 9:14 AM
> Steve,
>
> The answer to your question involves a discussion about how
> the K2 handles control of the power output level - in all
> cases, it tries to measure the actual power output and the
> microprocessor controls the drive level early in the
> transmit chain to achieve the power output requested by the
> power knob.
>
> Just as information about what is happening with that "RF
> Sensitivity" problem is that *if* some of the VHF/UHF energy
> appears on the K60XV TX output. That condition causes
> the RF detector on the K60XV to produce an output on the
> VRFDET line in the K2 (the detector is not frequency
> selective - it is just a diode, similar to an RF probe) -
> the result of all that is the K2 microprocessor ends up
> receiving a signal telling it that there is too much power
> at the TX output, and the microprocessor dutifully reduces
> the power.
>
> The simple low pass filter is just as effective at curing
> that condition as a unity gain buffer stage would be.
>
> The ideal solution would be to modify the transverter so
> that none of its output frequency energy appears on the
> input cable, but that is not realistic in some situations -
> it all depends on the transverter.
>
> 73,
> Don W3FPR
>
> On 11/8/2011 8:15 AM, Steve Kavanagh wrote:
> > My apologies regarding the link...as W1RT correctly
> figured out there should be an L at the end of it:
> >
> > www.qsl.net/ve3sma/downloads.html
> >
> > I had seen Don's circuit and decided to go a different
> route...not having to dig into the K2 was a plus for me (and
> I had a good supply of the Omron G5Y PC-board-mount RF
> relays).
> >
> > I had wondered how W1RT dealt with the RF sensitivity
> of the transverter out line....now I know ! I have
> been thinking lately a better solution than the filter might
> be a high isolation buffer amp with 0dB gain (or an
> attenuator and then a buffer with gain) built into the K2,
> but I haven't started looking to see where there might be
> room.
> >
> > 73,
> > Steve VE3SMA
> >
>

Don Wilhelm-4

Re: [K2] Solutions for K2 Transverter Quirks

Steve,

The problem I mentioned shows up more often at 432 MHz, but rarely at 144.

Given your particular problem, yes, if there is a voltage during receive
on the VRFDET signal input to the microprocessor, both transmit and
receive are disabled. Wayne put that into the firmware to protect the
receiver. It should not switch into transmit, but the receiver acts
like it is in transmit.

Considering the source of your VHF energy, I would think that a low pass
filter on the RX jack (as well as one "just in case" on the TX jack)
would take care of that problem. If it does, then any other work on the
K2 internals would be more complex, and I would recommend leaving it
alone - unless you just want to experiment with it. If the latter is
the case, contact me off-reflector and I will help you analyze it.

73,
Don W3FPR

On 11/8/2011 1:33 PM, Steve Kavanagh wrote:

> Don:
>
> Thanks for your comments (and since we haven't corresponded in a while....for your ongoing amazing help to all Elecraft owners through the email reflector).
>
> Actually, the issues I have had with the TX IF port have all been while receiving (with another nearby rig transmitting on VHF...or other signal source), so they do not have anything to do with the transmit power itself. The K2 seems to interpret a bit of power showing on the VRFDET line when in receive mode as a dangerous overload condition (as it would be if it appeared on the much less sensitive detector at the 10W antenna jack....and switches the rig (mostly) into transmit.
>
> I suppose a high field strength leakage from a nearby transmitter could indeed affect the transmit power as well....I haven't knowingly observed that.
>
> I have been working on a 10 GHz transverter (modifying a commercial radio) which will have a 21 MHz IF....which got me thinking about having a broadband solution to the RFI problems, so I wouldn't have to use two different filters to avoid the K2 being upset by nearby talkback link transmissions on 2m. I suppose a low pass filter is another option, but it is more difficult to get a sharp cutoff between 28 and 50 MHz than with a bandpass filter. An even better solution would probably be to apply a bias to the detector circuitry in the K60XV, while in receive mode, which prevents it from operating....but I haven't looked into the feasibility of this.
>
> 73,
> Steve VE3SMA
>
> --- On Tue, 11/8/11, Don Wilhelm<[hidden email]> wrote:
>
>> From: Don Wilhelm<[hidden email]>
>> Subject: Re: [Elecraft] [K2] Solutions for K2 Transverter Quirks
>> To: "Steve Kavanagh"<[hidden email]>
>> Cc: [hidden email]
>> Received: Tuesday, November 8, 2011, 9:14 AM
>> Steve,
>>
>> The answer to your question involves a discussion about how
>> the K2 handles control of the power output level - in all
>> cases, it tries to measure the actual power output and the
>> microprocessor controls the drive level early in the
>> transmit chain to achieve the power output requested by the
>> power knob.
>>
>> Just as information about what is happening with that "RF
>> Sensitivity" problem is that *if* some of the VHF/UHF energy
>> appears on the K60XV TX output. That condition causes
>> the RF detector on the K60XV to produce an output on the
>> VRFDET line in the K2 (the detector is not frequency
>> selective - it is just a diode, similar to an RF probe) -
>> the result of all that is the K2 microprocessor ends up
>> receiving a signal telling it that there is too much power
>> at the TX output, and the microprocessor dutifully reduces
>> the power.
>>
>> The simple low pass filter is just as effective at curing
>> that condition as a unity gain buffer stage would be.
>>
>> The ideal solution would be to modify the transverter so
>> that none of its output frequency energy appears on the
>> input cable, but that is not realistic in some situations -
>> it all depends on the transverter.
>>
>> 73,
>> Don W3FPR
>>
>> On 11/8/2011 8:15 AM, Steve Kavanagh wrote:
>>> My apologies regarding the link...as W1RT correctly
>> figured out there should be an L at the end of it:
>>> www.qsl.net/ve3sma/downloads.html
>>>
>>> I had seen Don's circuit and decided to go a different
>> route...not having to dig into the K2 was a plus for me (and
>> I had a good supply of the Omron G5Y PC-board-mount RF
>> relays).
>>> I had wondered how W1RT dealt with the RF sensitivity
>> of the transverter out line....now I know ! I have
>> been thinking lately a better solution than the filter might
>> be a high isolation buffer amp with 0dB gain (or an
>> attenuator and then a buffer with gain) built into the K2,
>> but I haven't started looking to see where there might be
>> room.
>>> 73,
>>> Steve VE3SMA
>>>
> ______________________________________________________________
> 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
>

Steve Kavanagh

Re: [K2] Solutions for K2 Transverter Quirks

--- On Tue, 11/8/11, Don Wilhelm wrote:

> Considering the source of your VHF energy, I would think that a low pass
> filter on the RX jack (as well as one "just in case" on the TX jack)
> would take care of that problem.

Actually, Don, it's the other way round. The offending detector is on the TX IF output, so it is the one needing filtering (even though the undesired behaviour is ostensibly protecting the receiver). I haven't found any need to filter the RX input jack to the K60XV...though perhaps in a multioperator station it might help clear up inter-station interference.

73,
Steve VE3SMA
______________________________________________________________
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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