Elecraft

[K2] Transmit Audio Problems

Classic

List

Threaded

9 messages Options

Michael Eberle

[K2] Transmit Audio Problems

I recently started trying to use my K2 for digital modes and noticed my
transmit audio seems to have some buzz or him in it. I never really
noticed it before on SSB, but if I listen carefully it sounds robotic,
like talking in front of a fan. When monitoring the SSB signal on my
K3/P3, I noticed that the carrier is not fully suppressed. It is
adjusted as low as it will go with the carrier balance pot on the SSB
board.

Do I have my filters set incorrectly or should I be checking for
assembly errors such as toroids wound wrong, wrong component values, or
bad solder joints?

Thanks,
Mike
KI0HA
______________________________________________________________
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
Message delivered to [hidden email]

Jim Brown-10

Re: [K2] Transmit Audio Problems

On 6/3/2014 4:54 PM, Michael Eberle wrote:
> It is adjusted as low as it will go with the carrier balance pot on
> the SSB board.

I suspect a simple problem with the audio interface. Study my tutorial
on this.

http://audiosystemsgroup.com/HamInterfacing.pdf

What sounds like inadequate carrier suppression could be AC hum/buzz due
to failure to bond the chassis of the computer to the chassis of the
radio. You also need a "pad" between the computer and the mic input.

A "pad" is another name for a simple voltage divider. It takes a series
resistor plus a parallel resistor across the input of the mic. Values
are not critical, but I would start with a 10:1 ratio, with the series
resistor being the larger value. 1K ohms series and 100 ohms parallel
would work fine. So would 470 and 47. There's no power being dissipated,
so small wattage resistors work fine. Exact values are not critical, so
you can use 20%, 10% or 5%, whatever you have.

Setting levels both at the computer and at the radio are critical. Study
the tutorial for more detailed advice.

73, Jim K9YC

______________________________________________________________
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
Message delivered to [hidden email]

Don Wilhelm-4

Re: [K2] Transmit Audio Problems

In reply to this post by Michael Eberle

Mike,

I can't say for certain, but yes, your carrier balance may not be
optimized *and* your SSB OP1 filter settings may not be correct. Either
or both could cause the condition you state.

Carrier Balance - you do not have to connect a mic when doing that - the
mic may pick up ambient noise which will mask the balance point.
All you need to do is close the PTT line, so plug a key (or paddles)
into the key jack and close the DOT paddle while in SSB mode (which will
assert PTT without any audio). Monitor the RF output from the K2 with a
monitor receiver or on a 'scope set for a very sensitive vertical gain
and adjust the pot for minimum RF output. You may have to compromise
between LSB and USB - start with LSB first and then check USB.

Once you have accomplished the carrier suppression, then you should turn
your attention to the passband positioning of the K2's OP1 filter in the
LSB and USB FL1 positions - those are what is used for transmit.

The KSB2 manual gives you some 'bogey values' for the BFO settings based
on your KSB2 crystal set.
You can do better if you refine those settings by using a wideband noise
generator and an audio spectrum analyzer like Spectrogram to view the
position of the passband.
See my webpage (www.w3fpr.com) article on K2 Dial Calibration for
further information and the Tom Hammond N0SS (SK) website at
http://www.mmccs.com/mmarc/n0ss/ for information about using Spectrogram
to align the K2 filters. Note that this is a static website - none of
the kits mentioned are available since Tom's passing, but the
information is valuable. For basics, the low frequency corner of the
SSB passband should be positioned close to 300 Hz.

If you do not have a wideband Noise Generator such as the Elecraft
N-Gen, you can use antenna noise on a dead band when aligning the
filters - be certain that there are no signals within the passband.
If you want to construct an easy wideband noise generator, take a look
at the information at http://www.mmccs.com/mmarc/n0ss/index_ele_kits.html
Note that kits are not available since Tom is SK, but the circuit is
easy to construct with 'flying leads', perfboard, and several other methods.

73,
Don W3FPR
On 6/3/2014 7:54 PM, Michael Eberle wrote:

> I recently started trying to use my K2 for digital modes and noticed
> my transmit audio seems to have some buzz or him in it. I never
> really noticed it before on SSB, but if I listen carefully it sounds
> robotic, like talking in front of a fan. When monitoring the SSB
> signal on my K3/P3, I noticed that the carrier is not fully
> suppressed. It is adjusted as low as it will go with the carrier
> balance pot on the SSB board.
>
> Do I have my filters set incorrectly or should I be checking for
> assembly errors such as toroids wound wrong, wrong component values,
> or bad solder joints?
>
> Thanks,
> Mike
> KI0HA

______________________________________________________________
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
Message delivered to [hidden email]

Michael Eberle

Re: [K2] Transmit Audio Problems

Okay, I have gone through all the filters and adjusted them using a
noise source and spectrogram. The carrier showing up on PTT in USB or
LSB has disappeared but I think this went away with installing the top
cover.

I still have problems with the audio. I set the dial frequency to
14200.00 USB and transmit a 700Hz tone. Monitoring the transmitted
signal with my K3 and P3 this is what I see. The expected spike at
14200.70, another shorter spike at 14.201.40, and another small spike at
14.202.10 -- exact multiples (harmonics) of the original 700Hz tone.
These spikes show up on all bands but 20 is the only band I have
actually used the P3 markers to measure.

What should I be checking for that could cause this?

Thanks,
Mike - KI0HA

On 6/3/2014 7:38 PM, Don Wilhelm wrote:
> Mike,
>
> I can't say for certain, but yes, your carrier balance may not be
> optimized *and* your SSB OP1 filter settings may not be correct.
> Either or both could cause the condition you state.
>

______________________________________________________________
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
Message delivered to [hidden email]

Michael Eberle

Re: [K2] Transmit Audio Problems

Aha, I think I found it. It appears that I have swapped C14 (22uF) with
C50 (2.2uF).

On 6/6/2014 11:09 PM, Michael Eberle wrote:

>
> Okay, I have gone through all the filters and adjusted them using a
> noise source and spectrogram. The carrier showing up on PTT in USB or
> LSB has disappeared but I think this went away with installing the top
> cover.
>
> I still have problems with the audio. I set the dial frequency to
> 14200.00 USB and transmit a 700Hz tone. Monitoring the transmitted
> signal with my K3 and P3 this is what I see. The expected spike at
> 14200.70, another shorter spike at 14.201.40, and another small spike
> at 14.202.10 -- exact multiples (harmonics) of the original 700Hz
> tone. These spikes show up on all bands but 20 is the only band I
> have actually used the P3 markers to measure.
>
> What should I be checking for that could cause this?
>
> Thanks,
> Mike - KI0HA
>

Phil Wheeler-2

Re: [K2] Transmit Audio Problems

Good job, Mike. Caps are pretty easy to mix up;
I've done that several times.

Phil W7OX

On 6/7/14, 12:54 AM, Michael Eberle wrote:

>
> Aha, I think I found it. It appears that I have
> swapped C14 (22uF) with C50 (2.2uF).
>
>
> On 6/6/2014 11:09 PM, Michael Eberle wrote:
>> I still have problems with the audio. I set
>> the dial frequency to 14200.00 USB and transmit
>> a 700Hz tone. Monitoring the transmitted
>> signal with my K3 and P3 this is what I see.
>> The expected spike at 14200.70, another shorter
>> spike at 14.201.40, and another small spike at
>> 14.202.10 -- exact multiples (harmonics) of the
>> original 700Hz tone. These spikes show up on
>> all bands but 20 is the only band I have
>> actually used the P3 markers to measure.
>>
>> Thanks,
>> Mike - KI0HA

Michael Eberle

Re: [K2] Transmit Audio Problems

Unfortunately, switching the caps to their correct positions did not
solve the problem.

On 6/7/2014 9:22 AM, Phil Wheeler wrote:

> Good job, Mike. Caps are pretty easy to mix up; I've done that several
> times.
>
> Phil W7OX
>
> On 6/7/14, 12:54 AM, Michael Eberle wrote:
>>
>> Aha, I think I found it. It appears that I have swapped C14 (22uF)
>> with C50 (2.2uF).
>>
>>
>> On 6/6/2014 11:09 PM, Michael Eberle wrote:
>>> I still have problems with the audio. I set the dial frequency to
>>> 14200.00 USB and transmit a 700Hz tone. Monitoring the transmitted
>>> signal with my K3 and P3 this is what I see. The expected spike at
>>> 14200.70, another shorter spike at 14.201.40, and another small
>>> spike at 14.202.10 -- exact multiples (harmonics) of the original
>>> 700Hz tone. These spikes show up on all bands but 20 is the only
>>> band I have actually used the P3 markers to measure.
>>>
>>> Thanks,
>>> Mike - KI0HA
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]
>

Vic Rosenthal

Re: [K2] Transmit Audio Problems

What's the source of the 700 Hz tone? Are you sure it is clean?
If you reduce the level of the 700 Hz tone, do the spikes go down at the
same rate as the fundamental, or faster? If the latter, you may be
overdriving the K2.

On 6/7/2014 7:40 AM, Michael Eberle wrote:

>
> Unfortunately, switching the caps to their correct positions did not
> solve the problem.
>
> On 6/7/2014 9:22 AM, Phil Wheeler wrote:
>> Good job, Mike. Caps are pretty easy to mix up; I've done that several
>> times.
>>
>> Phil W7OX
>>
>> On 6/7/14, 12:54 AM, Michael Eberle wrote:
>>>
>>> Aha, I think I found it. It appears that I have swapped C14 (22uF)
>>> with C50 (2.2uF).
>>>
>>>
>>> On 6/6/2014 11:09 PM, Michael Eberle wrote:
>>>> I still have problems with the audio. I set the dial frequency to
>>>> 14200.00 USB and transmit a 700Hz tone. Monitoring the transmitted
>>>> signal with my K3 and P3 this is what I see. The expected spike at
>>>> 14200.70, another shorter spike at 14.201.40, and another small
>>>> spike at 14.202.10 -- exact multiples (harmonics) of the original
>>>> 700Hz tone. These spikes show up on all bands but 20 is the only
>>>> band I have actually used the P3 markers to measure.
>>>>
>>>> Thanks,
>>>> Mike - KI0HA
>>
>> ______________________________________________________________
>> 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
>> Message delivered to [hidden email]
>>
>
> ______________________________________________________________
> 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
> Message delivered to [hidden email]

--
Vic
______________________________________________________________
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
Message delivered to [hidden email]

k6dgw

Re: [K2] Transmit Audio Problems

Anything other than a *perfect* sine wave will have harmonics which will
also appear in the output spectrum. Non-linearities within the radio
will also create extraneous products in the output.

With a P3 or other panadapter, take a look at WWV with the radio in AM
and the span around 6 or 7 KHz. They create a single audio baseband
that has all the bleeps, bloops, tones, 100 Hz subcarrier, IRIG-H
modulation and voice announcements, and modulate 5 transmitters with it.

The 2.5 and 20 MHz signals will look pretty much like we all expect:
The carrier surrounded very close by the two sidebands from the IRIG
subcarrier, and when the tones are on, they clearly show up, and the
spectrum is very clean. These two transmitters are apparently low-level
modulated with linear amplification.

The spectrum on 5, 10, and 15 MHz is altogether different. You will see
the carrier of course, surrounded very close by the IRIG subcarrier.
You will see the two expected sidebands from the tones when they're on.
You will also see harmonics of the tone sidebands ... depending on
conditions and time of day, I can sometimes see the 4th harmonic. Each
of the tone sidebands will have the subcarrier sidebands close around
them, as will all the harmonics. I believe these three transmitters are
Class C finals plate modulated or at least that's what I read.

The difference is really striking. It's amazing what a little
non-linearity can accomplish. :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

On 6/7/2014 11:02 AM, Vic Rosenthal wrote:
> What's the source of the 700 Hz tone? Are you sure it is clean?
> If you reduce the level of the 700 Hz tone, do the spikes go down at the
> same rate as the fundamental, or faster? If the latter, you may be
> overdriving the K2.

______________________________________________________________
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
Message delivered to [hidden email]