[Elecraft] Progress Report - Updated install info for LED CW Tuning Indicator using the K2's 10th S-meter LED

Tue Sep 28 00:41:43 EDT 2004

Hi folks:

Well, after about 4 years of having sold the PC boards for either the KR5L 
or the K6XX LED CW Tuning Indicator, I finally got around to building one 
for myself and test-fitting it into my (loaded) K2.

First, and most important... IT FITS!!! But barely!

Secondly, IT WORKS... and better than I'd anticipated.

Here's what I did... kinda abbreviated, but not all that much:

Always working from back to front (as is my backwards style), I first 
assembled the K6XX (XR2211-based) LED CW Tuning Indicator and hay-wired it 
up the K2 on the bench, using an external LED, just to confirm that it'd 
work for me... It did.

Then I needed to figure out where to locate the PC board within my K2 which 
is pretty much loaded to the gills with KPA100 / K160RX / KXV60 / KSB2 / 
KNB2 / KDSP2...

I decided that it'd just about fit between the Front Panel and the Control 
Board IF I flush-trimmed all the component leads on the bottoms of BOTH of 
the K2 boards AND those of the Tuning Indicator PC board as well. This took 
time to complete, but was well worth the effort.

After the pedicure to the K2 PC boards and the Tuning Indicator, it just 
fit between the two K2 boards with essentially no room to spare. I 
immediately realized that I should have specified a slightly shorter 
multi-turn pot for the frequency setting pot... its (brass) tuning shaft 
touched the back side of the CTRL board, thus leaving room for an unwanted 
short.

I quickly fixed this problem AND a similar concern for any of the pads on 
the bottom of the Tuning Indicator board shorting out against the pads of 
the FP board, by appropriate installations of paper insulation (fish paper) 
to the bottom of the CTRL board and to the bottom of the Tuning Indicator 
using a single small dollop of Goop to hold each piece of fish paper in 
place. After the paper was in place, the Tuning Indicator PC board fit in 
perfectly. At least on a test-fit basis at this juncture.

Then, on to actually connecting the Tuning Indicator to the K2...

Turns out that ALL(!) connections can be made to the FP board alone, making 
not only for an easy install but also one which doesn't require a bunch of 
fly-away wires running all over the place.

I picked up 5VDC from the PF board, just to the left of the S-meter LED bar 
graph, the access point for the 10th S-meter LED was pin 20 on the LED 
driver, GND was just to the right of the 2-meter LED bar graph, and AF 
Input came from the high end of the AF Gain pot (J1-2 or, as I used it, the 
fully clockwise terminal (VOL2) of the AF Gain pot itself).

That's all it took! I was amazed.

It took a bit of fiddling to find and center the PLL frequency on 600 Hz. I 
couldn't use my sidetone (as I'd hoped to do) since the sidetone's injected 
post-AF Gain control, so it wasn't available on the AF Gain control. 
Instead, I zero beated (is that a real/correct word?) a commercial carried 
(somewhere down below the bottom end of 20M CW) to my 600 Hz sidetone and 
used it as my tone against which I set the PLL frequency. I kept reducing 
the received signal level (via ATTEN and non-resonant antenna selection) to 
the point that I could just barely hear the signal in the speaker, and 
continued to refine my PLL freq. settings. As the signal gets weaker, the 
bandwidth of the PLL decreases, allowing you to get closer to being 'on 
freq' with each successive reduction in received signal level. Though... 
see the next paragraph...

I've found that the XR2211 is so darn sensitive that I was able to achieve 
a PLL lock on sin gals which were almost so far down in the mud that I 
couldn't hear them, much less copy them... and I thin I have a pretty good 
"CW ear". I believe the XR2211 does some low-level sign amplification and 
limiting internally, so my efforts to further reduce the signal level may 
not have had as much of a significant effect as I once though they did. But 
regardless, the PLL locks at about +/- 40Hz of the desired frequency, and 
this should be more than close enough for just about ANY zero beat 
application except the most very discerning operator.

Once I had the PLL frequency set, I dropped the PC board into the case, 
between the FP and CTRL boards and buttoned things back up... done!

This having been said, and now written about, I'm working on an SMD version 
of the K6XX CW Tuning Indicator. I have the PC board designed, and several 
prototypes etched. I have three of the SMD ICs in hand, with two more to 
come. But I've not yet ordered the other few components. I chose to use 
1206-size capacitors and resistors, because they were largest size I could 
reliably find... thus making it a bit easier for those of us with twelve 
thumbs to assemble the boards.

I'll be building this SMD version sometime soon... as soon as I can get the 
remaining parts ordered (and receive) from Mouser... I'll report on the 
success of this project. If it works (as I hope it will), the resulting PC 
board will be slightly less than 1/2 the rectangular size of the current 
thru-hole board, and about 1/3 as think... it'll slip in between the FP and 
CTRL boards with no complaint whatsoever. I've also included a 5-pin 
connector on the SMD board to allow it to be readily disconnected from the 
FP board, for easy removal when disassembling the K2 for any reason.