[Elecraft] K2 drif problems?

Sun Dec 15 16:13:03 2002

Well put ron,don`t forget the friend ships that are made through this
ref........and the hours of woulderful past time the elecraft  k1 and k2
have been for all of us,and the people at elecraft and there products, all
of which are great, thanks to every one who has made this what it is.
sincerely n5tog harold 73`
----- Original Message -----
From: "Ron D'Eau Claire" <[email protected]>
To: <[email protected]>
Sent: Sunday, December 15, 2002 12:49 PM
Subject: RE: [Elecraft] K2 drif problems?


> Ed, one thing you will see on the reflector consistently are comments
> and observations about how to make the Elecraft rigs better. The
> Elecraft engineers jump in quite often and more than a few changes and
> modifications have been made to the designs following what has gone on
> here. That's one of the big advantages of the Elecraft equipment over
> typical "factory built" rigs.
>
> Frequency drift in the K2 is one of those reoccurring issues. First it
> is important to understand that the K2 does NOT use a frequency
> synthesizer with a temperature-controlled crystal reference oscillator
> for "state of the art" frequency stability. While it uses a Phase-Locked
> Loop to generate the local oscillator signal, it accomplishes smooth
> tuning by using a variable frequency oscillator as the loop reference
> oscillator. That means that the frequency stability of the K2 is no
> better than the frequency stability of the simple, variable frequency
> oscillator.
>
> Elecraft uses a solid, stable design for that oscillator. Instead of a
> free-running variable frequency oscillator (VFO) they used a variable
> crystal oscillator (VXO) in which the frequency of a crystal-controlled
> oscillator is "pulled" to provide the tuning range necessary to cover
> the 5 kHz "steps" in the phase locked loop design.
>
> The VXO is a lot more stable than a simple VFO, but like any oscillator
> that can be shifted in frequency easily, it will tend to shift in
> frequency as the temperature changes - what we usually refer to as
> "drift". The beat-frequency oscillator (BFO) used in the i-f section of
> the receiver is also a VXO and is also subject to drift.
>
> Over the past two years I have followed several threads from ops who
> were trying to improve the overall frequency stability of the K2. Some
> of them simply wanted to see how good it could be made. Others had a
> serious issue with the drift in their K2's. Most of those were operating
> PSK-31. That mode really taxes the stability of any rig. A PSK31 signal
> only occupies 31 HZ of bandwidth!
>
> The concerns over the frequency stability of the K2 became a very common
> issue when the KPA100 amplifier module was finally released. That module
> makes a K2 a K2/100 with 100 watts PEP or CW output. It also creates a
> significant amount of heat. The whole top of the K2/100 is a heat sink,
> as you can see from the pictures. Those black ribs running front to back
> are the top of the heat sink. Almost immediately a number of ops with
> the early amplifier modules noted that the drift of the K2 was much
> greater, especially on certain bands where the combined drift of the BFO
> and VFO added to make the total drift greater than that of either
> oscillator alone . The KPA100 amplifier pumps quite a bit of heat inside
> the K2 where it warms up the components in the oscillators, making them
> move in frequency.
>
> In response to that, the basic K2 has been improved to reduce the drift.
> K2's newer than S/N 3000 have a number of improvements to reduce the
> drift of both the VXO and BFO. Elecraft release a kit for the owners of
> earlier K2's so they could incorporate these changes in their older
> radios.
>
> Recently I added the KPA100 module to my K2, along with the
> modifications to make it more stable. Then I ran some drift
> measurements. On 15 meters - one of the bands where the drift is the
> worst due to the mixing scheme used in the K2 - I find that it is
> disappointingly large. After allowing my K2 to warm up for half an hour,
> a CW QSO lasting half an hour of transmitting and receiving can result
> in 250 Hz of frequency drift in my K2. That's enough to have moved my
> signal outside of the passband of the other station's filters if he were
> using a really narrow filter. It's certainly enough to cause the other
> operator to "touch up" the tuning in many cases.
>
> That is on the band where the drift is the worst, however. I ran some
> quick checks and it seems to be about half that on 40 meters, for
> example. About 100 Hz.
>
> Even that is enough to cause some re-tuning in either CW or SSB. For
> PSK-31, it's a really significant amount of drift, and from time to time
> you will see a lot of comments on here as ops work on ways to reduce it.
> That said, that amount of drift in a rig is not at all unusual on the
> Ham bands.
>
> Compared to the rigs of a few decades ago, the K2 has "laboratory
> standard stability". But this is not 1960 and I'm not using my HRO-5
> receiver filled with tubes either. Compared to the state-of-the-art rigs
> today, the K2's frequency stability is competitive but a lot of
> factory-built rigs are better. In true Ham fashion, many ops on this
> reflector are of the opinion that the K2 can do better and are working
> on ways to make it more stable. The beauty of the Elecraft rig is that
> the engineers who designed it are also working on ways to make it more
> stable and they participate in this reflector.
>
> In my view, the K2 is a very good rig. It's nothing magic. It's
> certainly not without faults. I've never seen a piece of equipment that
> is. The biggest feature that Elecraft has to offer, in my opinion, is
> their on-going support to the community of Hams who always want to make
> it a "little better"...  So we jawbone and fuss over things like making
> it more stable. That's what some Hams do as much as they operate. I
> guess that I'm one of those.
>
> If it weren't for those of us who want to see it work a little "better"
> , this reflector probably would be a pretty dead place. There isn't much
> in the way of other "problems" to discuss about the K2. Oh, there is the
> other reoccurring issue of a "better" tuning knob - one with smooth
> rounded edges and a dimple for "twirling". But  that's been "solved" for
> those ops with a replacement knob from a Japanese rig. Personally, I
> like the nicely-weighted "stock" K2 knob, so don't worry about that too
> much. I always figured that if the worst issue people had to work on was
> the design of the tuning knob, the rig must be pretty good.
>
> For me, the next thing I want to do is to  KILL that #$%@# little fan in
> the KPA100. To me, it has all the attributes of a crazed mosquito in the
> room. Ah... but that's another "enhancement" to think about another
> day...
>
> Ron AC7AC
> K2 # 1289
>
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