Re: K1 Future Improvements to VFO D3, R17,R18 any one tried??

[Mike Morrow-3]

Don wrote:

>I would not regard 100 Hz of drift in the K1 as a design problem at all -
>The K1 spec is for drift less that 200 Hz after a 5 minute warmup.
>
>The fact that the K1 does not use a DDS vfo is not a 'design problem'
>as was stated...

I wholeheartedly agree.  I had been using (and still use) three of SWL's wonderful DSW-series mono-band DDS rigs before I got my K1 in late 2000.  I was fully prepared to be disappointed by the stability of the LC VFO design of the K1.  Instead, I quickly found that I was very pleased with the stability of the K1's VFO.

> but surely was a design decision based on price/performance with
>components available at the time it was designed.  At the time the K1 was
>designed, DDS units were not as available as today and were still quite
>pricy - by the time the KX1 was designed, the cost of DDS had dropped
>significantly.

I would express a different view.  I would hate to see the performance of the K1 *degraded* by the use of a DDS VFO.  After experiencing how well the K1's LC VFO performs, I would now NOT buy a K1 if it used a DDS frequency generation scheme such as that found in the KX1 or DSW.

A simple DDS VFO design such as is found in KX1 or DSW units puts a fair amount of spurious output directly into the higher level transmitter stages, and into the receiver mixer.  This junk degrades transmitter spurious output quality and receiver performance.  The K1's LC VFO and hetrodyne crystal oscillator output is far cleaner than any current DDS-only VFO.  Those who wish for every little enhancement possible in the RF performance of a radio will NOT choose a simple DDS VFO design.  More sophisticated rigs that use DDS use it in conjunction with a PLL to generate a much cleaner signal rather than using the direct raw output of a DDS chip.  Perhaps soon a combo DDS-PLL chip that is low-cost and low-power will arrive for use in our QRP rigs and reduce the concern about spurious output.

An additional issue arises from the requirement in the KX1 for the DDS to produce output frequencies over a very wide range as it changes band-to-band, mode-to-mode, and receive-to-transmit.  The KX1 DDS generates all of the required frequencies directly, rather than through hetrodyning with crystal oscillators.  The clocking rate for current low-cost low-power DDS chips like the KX1's AD9834 is limited to 50 MHz, and the maximum output frequency at that clock is about one-third of that (16.6 MHz).  This means that coverage of any ham band above 20m is fundamentally out of the question.  However, a simple DDS VFO has a few advantages over the LC VFO:  Excellent stability, resetability, wide frequency span, and adaptibility to digital control.  Only the first two are usually apparent to the operator.

OTOH, the step-wise incremental tuning and the manipulations required to change the tuning step make DDS VFO tuning far less natural than that of the continuous output of an LC VFO that tunes where and just as fast or slow as I turn the dial.

So the options are clear.  Choose the simple DDS rig if crystal-like temperature stability and resetability are most important to you.   Choose a LC VFO rig if overall RF performance and naturalness of tuning are most important to you.

> I fail to understand how anyone could refer to this a
> 'design problem'.

Agreed.  The *superior* performance of the LC VFO over the simple DDS VFO make it the choice of those for whom the RF signal performance of their radio is important.  It's a very *positive* design feature of the K1 over the KX1 that may go unrecognized by those unfamiliar with the technical issues at hand.

But returning back to the original question, I'd say that if anyone finds something simple that improves the already excellent stability of the K1 VFO, I'd certainly be interested in hearing about it.  Happy experimenting!

73,
Mike / KK5F

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[EricJ-2]

I completely agree with you, Mike. A DDS in the K1 would be a step backwards
in performance. I'm willing to put up with the annoying step-wise DDS tuning
in my KX1 for those times when I want a grab-and-go rig on a bicycle trip or
hike. But most of the time, I much prefer the silky smooth tuning of my K1.
As you say, it tunes more naturally and, to me, more melodiously consistent
with that same characteristic of CW. Tuning a DDS through several signals
near one another produces such a confusion of discrete tones that it is
often easy to lose sight of the guy you were trying to tune in. The K1 is a
keeper.

Eric
KE6US
www.ke6us.com  

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Mike Morrow
Sent: Monday, December 19, 2005 2:32 PM
To: [hidden email]
Subject: Re: [Elecraft] K1 Future Improvements to VFO D3, R17,R18 any
onetried??

Don wrote:

>I would not regard 100 Hz of drift in the K1 as a design problem at all
>- The K1 spec is for drift less that 200 Hz after a 5 minute warmup.
>
>The fact that the K1 does not use a DDS vfo is not a 'design problem'
>as was stated...

I wholeheartedly agree.  I had been using (and still use) three of SWL's
wonderful DSW-series mono-band DDS rigs before I got my K1 in late 2000.  I
was fully prepared to be disappointed by the stability of the LC VFO design
of the K1.  Instead, I quickly found that I was very pleased with the
stability of the K1's VFO.

> but surely was a design decision based on price/performance with
>components available at the time it was designed.  At the time the K1
>was designed, DDS units were not as available as today and were still
>quite pricy - by the time the KX1 was designed, the cost of DDS had
>dropped significantly.

I would express a different view.  I would hate to see the performance of
the K1 *degraded* by the use of a DDS VFO.  After experiencing how well the
K1's LC VFO performs, I would now NOT buy a K1 if it used a DDS frequency
generation scheme such as that found in the KX1 or DSW.

A simple DDS VFO design such as is found in KX1 or DSW units puts a fair
amount of spurious output directly into the higher level transmitter stages,
and into the receiver mixer.  This junk degrades transmitter spurious output
quality and receiver performance.  The K1's LC VFO and hetrodyne crystal
oscillator output is far cleaner than any current DDS-only VFO.  Those who
wish for every little enhancement possible in the RF performance of a radio
will NOT choose a simple DDS VFO design.  More sophisticated rigs that use
DDS use it in conjunction with a PLL to generate a much cleaner signal
rather than using the direct raw output of a DDS chip.  Perhaps soon a combo
DDS-PLL chip that is low-cost and low-power will arrive for use in our QRP
rigs and reduce the concern about spurious output.

An additional issue arises from the requirement in the KX1 for the DDS to
produce output frequencies over a very wide range as it changes
band-to-band, mode-to-mode, and receive-to-transmit.  The KX1 DDS generates
all of the required frequencies directly, rather than through hetrodyning
with crystal oscillators.  The clocking rate for current low-cost low-power
DDS chips like the KX1's AD9834 is limited to 50 MHz, and the maximum output
frequency at that clock is about one-third of that (16.6 MHz).  This means
that coverage of any ham band above 20m is fundamentally out of the
question.  However, a simple DDS VFO has a few advantages over the LC VFO:
Excellent stability, resetability, wide frequency span, and adaptibility to
digital control.  Only the first two are usually apparent to the operator.

OTOH, the step-wise incremental tuning and the manipulations required to
change the tuning step make DDS VFO tuning far less natural than that of the
continuous output of an LC VFO that tunes where and just as fast or slow as
I turn the dial.

So the options are clear.  Choose the simple DDS rig if crystal-like
temperature stability and resetability are most important to you.   Choose a
LC VFO rig if overall RF performance and naturalness of tuning are most
important to you.

> I fail to understand how anyone could refer to this a 'design
> problem'.

Agreed.  The *superior* performance of the LC VFO over the simple DDS VFO
make it the choice of those for whom the RF signal performance of their
radio is important.  It's a very *positive* design feature of the K1 over
the KX1 that may go unrecognized by those unfamiliar with the technical
issues at hand.

But returning back to the original question, I'd say that if anyone finds
something simple that improves the already excellent stability of the K1
VFO, I'd certainly be interested in hearing about it.  Happy experimenting!

73,
Mike / KK5F

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[Lambs, Dick & Judy]

There is one very simple solution to greatly improve the stability of  
any VFO:  blowing air over the equipment case. It's not obvious, but  
by keeping the case cool, you keep air inside the case close to  
ambient temperature.   The stability gain can be incredible--around  
an order of magnitude.  I like to think it also reduces the chance of  
component failure due to to heat.

You can place the fan on a stand behind or next to the transceiver to  
blow over the top.  I place the fan right on the top, horizontally,  
raised with spacers in each of the fan's mounting holes.  (No holes  
in the case--just gravity holding the fan.)  I drop the voltage to  
the fan to about 50% to 75% to keep it quiet.

I've not tried this with a K1, but it sure works with other  
transceivers.

73
Dick, K0KK

On Dec 19, 2005, at 4:31 PM, Mike Morrow wrote:

>
> But returning back to the original question, I'd say that if anyone  
> finds something simple that improves the already excellent  
> stability of the K1 VFO, I'd certainly be interested in hearing  
> about it.  Happy experimenting!
>
> 73,
> Mike / KK5F
>
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