[Elecraft] 5 KHZ dead spots

[W0MU Mike Fatchett]

Interesting information.

I guess I did not hear it on 160 as I did not have loud signals close to the
pll frequency.

I really don't understand the motivation of the so called non invested ($$$)
experts on the list.  The K3 won't get better if we do not provide feedback
on our own experiences.  Everyone uses THEIR radio differently so they may
experience situations others may not.

I am quite interested to see if and how the pile up mush issue will be
addressed.  Enough of us have seen it to warrant some kind of investigation.

W0MU 


"A slip of the foot you may soon recover, but a slip of the tongue you may
never get over." Ben Franklin
-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Merv Schweigert
Sent: Wednesday, February 25, 2009 10:42 AM
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] 5 KHZ dead spots

Thanks very much Wayne for the explanation . Its not really a problem as you
say. If tuning very fast you also hear it pop as you pass those points.
Majority of the time it is covered either with band noise or with signals.

You mentioned it being heard only if there was a moderate to strong signal
in the passband,  I hear it with no signals at all in the passband, usually
the band noise on 160 covers it up or QRN,  last nite was a very quiet nite
and I could hear it with no signals within 25 khz,  and those signals were
S2 at loudest. 

It is not a problem,  just something I noticed and was curious about the
cause.

Proves a point also,  some of the experts on the list pull the trigger
without a target in site or without knowing what they are shooting at.  Old
proverb,  "you dont know what my radio sounds like unless you have worn the
headphones for a moon".  
Dont jump on the little pistols for bringing up problems or questions, you
may find out some of them are more qualified than you to make a comment. 
And for the others who have drank the kool aide without any questions,
sorry.
K3 is superior in many ways to all the radios avaliable,  its not perfect,
there will never be one that suits all,  but for what I use it for its
pretty close,  Only reason to bring up shortfalls is to make it the best
there is, As soon as I see a APF function and the pile up "mush" problems go
away,  It will be hard to make any more comments for what I use the radio
for. 
For those who miss the APF and are missing contacts due to not having one,
I have hung a Datong FL-2 on the K3,  it works best of all I have
tried so far,  (autek etc).   But the tuning is pretty sharp with small
knobs.  But it does work almost as well as the FT-1000D old original
APF.   But thats another subject in itself.  
Thanks again to Wayne for explaining what #2306 is hearing that 2,999 others
dont.  :o)
73 Merv KH7C  (K9FD)






wayne burdick wrote:
> Merv Schweigert wrote:
>
>> Have noticed this on other bands but paid no particular attention, 
>> but today was tuning 160 meters and every 5 khz there is a pop or 
>> change in background receiver noise when tuning.
>
> Hi Merv,
>
> This is normal. The K3 has an incredibly low-noise analog/digital 
> synthesizer. To achieve this performance, we have to use a fairly 
> low-frequency PLL loop (~22 kHz). This translates into a little 
> artifact in the VFO tuning range every 22 kHz, on average, across the 
> ham bands. Nearly all other PLL-based rigs have such transitions at 
> much wider spacing, because they use up-conversion to a VHF 1st IF and 
> thus much higher synthesizer output frequencies. But this results in 
> inferior performance, generally, and doesn't support narrow roofing 
> filters. (For example, most rigs on the market have a roofing filter 
> in the 4 to 15 kHz wide range, compared to as low as 200 Hz in the K3.
> Our down-conversion scheme, to an 8.215 MHz IF, is the reason we can 
> do this.)
>
> The tuning artifact is only noticeable if a moderate to strong signal 
> is in the passband as you tune across it. When you stop tuning, it's 
> gone. And while you're tuning, we do a partial mute of the receiver 
> (actually, we engage a low-threshold limiter for about 10 ms). This 
> makes it barely noticeable in most cases, which is why, with nearly 
> 3000 K3s shipped, you've never heard a description of it until now :)
>
> The actual spacing of the tuning artifacts varies on a per-band basis, 
> being smaller on the lower bands. The reason for this is a bit 
> complicated. We shoe-horn the reference signal for the PLL (i.e. the 
> DDS, the source of fine-tuning steps) through a 2.5 kHz crystal filter 
> to ensure there are no DDS spurs in the VCO output. 2.5 kHz is a lot 
> narrower than 22 kHz. So we have to constantly adjust the PLL divider 
> values (N and R dividers, to be precise) so that our DDS signal always 
> stays within the crystal filter, yet allows the PLL to generate a wide 
> enough frequency range to cover the segment of interest. We used a 
> home-brew PC program to pre-calculate the optimal N and R divider 
> values for the entire tuning range, and we store them in about 30 kb 
> of the front panel flash memory chip. As you tune the VFO, we look up 
> the table values.
>
> This works smoothly, but as you noted, you might hear a soft "blip" 
> under just the right circumstances as you cross one of the transition 
> points. It's a little reminder of what it takes to create a very 
> quiet, high-dynamic-range RX.
>
> 73,
> Wayne
> N6KR
>
>
> ---
>
> http://www.elecraft.com
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html