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K2 -15Mtr birdies?

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R Thompson

K2 -15Mtr birdies?

I hadn't noticed this before as I don't normally operate in this part
of 15 metres. As I tuned across 15 metres I noticed a couple of
birdies, switching between the antenna and dummy load didn't make
them go away. They're weak, at the bottom of the S meter, but I
don't know if this is normal, or if there is something I could do
about them. On CW mode the first is at 21028.63 KHz and the tone
changes rapidly, maybe 100Hz or more for every 10Hz change on the
tuning. The second one is at around 21036.20 KHz. Is this normal,
and is there a fix for it? Maybe there are others on other bands
that I'm not yet aware of.

Ron VE8RT [hidden email]
Yellowknife, NT, Canada
62 26.765N 114 22.503W Grid Square DP22tk
"Who are these that fly as a cloud, and as doves to their window?"
Is 60:8

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Geoffrey Mackenzie-Kennedy-3

Re: K2 -15Mtr birdies?

Ron,

You asked if it is normal to hear birdies, the short answer is "not always".
Most superhet receivers, but certainly not all designs, will be affected by
birdies. Unfortunately many if not most of the receivers designed for the
amateur market use an "open plan" layout without shielding nor decoupling
filters perhaps for reasons of cost, and that will inevitably result in
birdies being heard. Unfortunately the K2 does have a birdie problem.

You asked if there was something you could do about the weak birdies you
found at 21028.63 kHz and 21036.20 kHz. Again my answer is yes, but I must
warn you that getting rid of these and the other birdies found in the K2 is
not an easy task, and requires "surgery". Some years ago I got rid of the
birdies in my K2/100, but it required the addition of some shielding,
breaking some DC supply and control traces and inserting L-C filters, moving
some bypass ground points, etc etc.

Knowing the tuning rate of a birdie vs. the VFO tuning rate is useful
information. One type of birdie, and there are different breeds, appears
when a spurious response of the receiver (the so-called image is one of
many) "hears" an oscillator, or a harmonic of an oscillator. The tuning
rate of this type of birdie will sometimes provide a clue as to which
oscillator or mix of oscillators is responsible, and which of the receiver's
responses is "hearing" it. To cite a simple example, if the BFO frequency
is 4.914 MHz, there are three possible birdies ganging up at 21.294 MHz, due
to the BFO's fundamental, BFO x 3 and BFO x 9 being heard by three different
spurious responses. The birdie tuning rates in this case are 1/3, 1 and 3
because the third harmonic of the LO is involved.

Please do not hesitate to ask if I can help in any way.

73,

Geoff
LX2AO

On May 11, 2012 at 04:40 +0200, Ron VE8RT wrote:

>I hadn't noticed this before as I don't normally operate in this part
> of 15 metres. As I tuned across 15 metres I noticed a couple of
> birdies, switching between the antenna and dummy load didn't make
> them go away. They're weak, at the bottom of the S meter, but I
> don't know if this is normal, or if there is something I could do
> about them. On CW mode the first is at 21028.63 KHz and the tone
> changes rapidly, maybe 100Hz or more for every 10Hz change on the
> tuning. The second one is at around 21036.20 KHz. Is this normal,
> and is there a fix for it? Maybe there are others on other bands
> that I'm not yet aware of.

______________________________________________________________
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

R Thompson

Re: K2 -15Mtr birdies?

Thanks Geoff,

yours is the second reply I've had letting me know that there are
birdies in the K2 receiver. It answers my question as to whether or not
I overlooked something in the assembly or if this was a known condition.

I say condition and not problem as the level and location of the
birdies is unlikely to be a problem.

Tomorrow I'm leaving for two weeks, we're heading to VO1 to visit our
oldest son. I may re-visit this a little later and do some more
research. The loudest one changes in frequency steps much greater than
the steps on the dial, it may then be easier to find it's source. If
its a relatively easy fix I may look into doing it and will gladly
accept your offer of help.

Thanks & 73 Ron VE8RT

On Sat, 2012-05-12 at 20:43 +0200, Geoffrey Mackenzie-Kennedy wrote:

> Ron,
>
> You asked if it is normal to hear birdies, the short answer is "not always".
> Most superhet receivers, but certainly not all designs, will be affected by
> birdies. Unfortunately many if not most of the receivers designed for the
> amateur market use an "open plan" layout without shielding nor decoupling
> filters perhaps for reasons of cost, and that will inevitably result in
> birdies being heard. Unfortunately the K2 does have a birdie problem.
>
> You asked if there was something you could do about the weak birdies you
> found at 21028.63 kHz and 21036.20 kHz. Again my answer is yes, but I must
> warn you that getting rid of these and the other birdies found in the K2 is
> not an easy task, and requires "surgery". Some years ago I got rid of the
> birdies in my K2/100, but it required the addition of some shielding,
> breaking some DC supply and control traces and inserting L-C filters, moving
> some bypass ground points, etc etc.
>
> Knowing the tuning rate of a birdie vs. the VFO tuning rate is useful
> information. One type of birdie, and there are different breeds, appears
> when a spurious response of the receiver (the so-called image is one of
> many) "hears" an oscillator, or a harmonic of an oscillator. The tuning
> rate of this type of birdie will sometimes provide a clue as to which
> oscillator or mix of oscillators is responsible, and which of the receiver's
> responses is "hearing" it. To cite a simple example, if the BFO frequency
> is 4.914 MHz, there are three possible birdies ganging up at 21.294 MHz, due
> to the BFO's fundamental, BFO x 3 and BFO x 9 being heard by three different
> spurious responses. The birdie tuning rates in this case are 1/3, 1 and 3
> because the third harmonic of the LO is involved.
>
> Please do not hesitate to ask if I can help in any way.
>
> 73,
>
> Geoff
> LX2AO
>
>
> On May 11, 2012 at 04:40 +0200, Ron VE8RT wrote:
>
>
> >I hadn't noticed this before as I don't normally operate in this part
> > of 15 metres. As I tuned across 15 metres I noticed a couple of
> > birdies, switching between the antenna and dummy load didn't make
> > them go away. They're weak, at the bottom of the S meter, but I
> > don't know if this is normal, or if there is something I could do
> > about them. On CW mode the first is at 21028.63 KHz and the tone
> > changes rapidly, maybe 100Hz or more for every 10Hz change on the
> > tuning. The second one is at around 21036.20 KHz. Is this normal,
> > and is there a fix for it? Maybe there are others on other bands
> > that I'm not yet aware of.
>

Don Wilhelm-4

Re: K2 -15Mtr birdies?

Ron,

The K2 uses VFO frequencies above the incoming signal for bands below 15
meters, and that helps keep the "birdies at bay". On 15 meters and
above, the VFO is below the incoming signal which is not the greatest
situation for birdies, but provides better VFO stability - read as a
design decision.
The major birdies are outside the ham bands, but there are a few low
level birdies left inside the ham bands. As Geoff has indicated, they
can be dealt with, but the solution is not trivial.

73,
Don W3FPR

On 5/12/2012 5:57 PM, R Thompson wrote:

> Thanks Geoff,
>
> yours is the second reply I've had letting me know that there are
> birdies in the K2 receiver. It answers my question as to whether or not
> I overlooked something in the assembly or if this was a known condition.
>
> I say condition and not problem as the level and location of the
> birdies is unlikely to be a problem.
>
> Tomorrow I'm leaving for two weeks, we're heading to VO1 to visit our
> oldest son. I may re-visit this a little later and do some more
> research. The loudest one changes in frequency steps much greater than
> the steps on the dial, it may then be easier to find it's source. If
> its a relatively easy fix I may look into doing it and will gladly
> accept your offer of help.
>
> Thanks& 73 Ron VE8RT
>
> On Sat, 2012-05-12 at 20:43 +0200, Geoffrey Mackenzie-Kennedy wrote:
>> Ron,
>>
>> You asked if it is normal to hear birdies, the short answer is "not always".
>> Most superhet receivers, but certainly not all designs, will be affected by
>> birdies. Unfortunately many if not most of the receivers designed for the
>> amateur market use an "open plan" layout without shielding nor decoupling
>> filters perhaps for reasons of cost, and that will inevitably result in
>> birdies being heard. Unfortunately the K2 does have a birdie problem.
>>
>> You asked if there was something you could do about the weak birdies you
>> found at 21028.63 kHz and 21036.20 kHz. Again my answer is yes, but I must
>> warn you that getting rid of these and the other birdies found in the K2 is
>> not an easy task, and requires "surgery". Some years ago I got rid of the
>> birdies in my K2/100, but it required the addition of some shielding,
>> breaking some DC supply and control traces and inserting L-C filters, moving
>> some bypass ground points, etc etc.
>>
>> Knowing the tuning rate of a birdie vs. the VFO tuning rate is useful
>> information. One type of birdie, and there are different breeds, appears
>> when a spurious response of the receiver (the so-called image is one of
>> many) "hears" an oscillator, or a harmonic of an oscillator. The tuning
>> rate of this type of birdie will sometimes provide a clue as to which
>> oscillator or mix of oscillators is responsible, and which of the receiver's
>> responses is "hearing" it. To cite a simple example, if the BFO frequency
>> is 4.914 MHz, there are three possible birdies ganging up at 21.294 MHz, due
>> to the BFO's fundamental, BFO x 3 and BFO x 9 being heard by three different
>> spurious responses. The birdie tuning rates in this case are 1/3, 1 and 3
>> because the third harmonic of the LO is involved.
>>
>> Please do not hesitate to ask if I can help in any way.
>>
>> 73,
>>
>> Geoff
>> LX2AO
>>
>>
>> On May 11, 2012 at 04:40 +0200, Ron VE8RT wrote:
>>
>>
>>> I hadn't noticed this before as I don't normally operate in this part
>>> of 15 metres. As I tuned across 15 metres I noticed a couple of
>>> birdies, switching between the antenna and dummy load didn't make
>>> them go away. They're weak, at the bottom of the S meter, but I
>>> don't know if this is normal, or if there is something I could do
>>> about them. On CW mode the first is at 21028.63 KHz and the tone
>>> changes rapidly, maybe 100Hz or more for every 10Hz change on the
>>> tuning. The second one is at around 21036.20 KHz. Is this normal,
>>> and is there a fix for it? Maybe there are others on other bands
>>> that I'm not yet aware of.
>
> ______________________________________________________________
> 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
>