Re: K3 IF output

[K2QI]

Hi Dave,

 

I'll see what I can do to borrow another receiver.  Otherwise, your Softrock
suggestion seems perfect.

 

As for the chipped resistor; I seem to have taken a very small bit off the
surface at one corner.  It's the black material with the value etched on top
of it.  I guess the edge of my screwdriver chipped it off when I was
attempting to hold it down.  I'm surprised it chipped so easily as I did my
best not to apply too much pressure.  After soldering, I did test resistance
however, and got a reading of 13.4 k ohms.  That seems to be within a 5%
amount of variance.  I don't know what the tolerance range is for this part
though.  Should I replace this resistor with another, or use the leaded one
included with the kit?

 

Mni tnx es 73

James K2QI

 

  _____  

From: G3TJP [mailto:[hidden email]]
Sent: Wednesday, January 06, 2010 8:33 PM
To: [hidden email]
Subject: K3 IF output

 

I've been following your adventures re the mod to the IF output of the K3.

 

First of all, the signal present at the IF output is at the microvolt level
- pretty much a signal level that you'd expect to come from an antenna.

 

Rather than borrow a spectrum analyser, which may be quite difficult to
organise, why not borrow a receiver?  A spare rx. is of immense value.

 

If you can borrow a rx., connect its antenna input to the IF output, tune
the rx to 8.215MHz and then apply your 50uV signal to the K3 and tune it in,
first on the K3 and then on the borrowed Rx.  You should hear it tune in on
both receivers - the K3 and the loan radio, although the IF on the K3 isn't
necessarily spot on 8.215MHz.

 

You can tune the borrowed Rx across the K3's IF bandwidth, so there you have
it, the borrowed receiver is an aural spectrum analyser.

 

If you can't borrow a Rx., you could build one of the softrock software
defined radio modules that's designed for the K3 IF and use that with a
computer and free SDR software to listen to the K3's IF.  If you were
troubled by the Softrock's oscillator feedthrough, one of Jack Smith's
Clifton Laboratories Z10000 buffer amps would help.  Hey, if you build them
both, you have the structure for a panadapter using Rocky software and a
high quality soundcard in your computer.  I've built one and it works just
fine, but I haven't yet figured out how to do point and click on the
frequency display to control the K3's tuning HI!

 

The two kits I've mentioned are cheap!  One's around $15 and the other's
around $25, IIRC.  They will be a good intro into the world of SDR.

 

It's generally not a good thing to chip a bit off an SMT component.
Resistors are normally tiny bricks of ceramic that have a resistive coating
applied on one side (usually the top).  This is then whittled to the
required resistance by laser action.  The conductive ends are then sputtered
onto the chip.  The surface of the laser-cut resistive element is then epoxy
coated for protection.

 

The secret of SMT wrangling is to pin the little xxxx down using vertical
pressure.  My SMT pinning rig consists of a bent wire coathanger to form a
base with an arch (with kinks in it) until the last bit, which points
downwards.  To that end, I fix a cocktail stick (they're nice because the
tip doesn't usually skid on the SMT's surface, but you do get through quite
a few cocktail sticks HI!  The kinks are there to hold a couple of fishing
weights in place to provide downward pressure.  To join the stick to the
mutilated coathanger, I use the insert from a choc-block connector.  One
screw holds onto the coathanger and the other holds onto the cocktail stick.

It all boils down to having a means of applying pure vertical pressure on
the component you intend attaching.

 

For simple SMT rework involving removal of a component, Google Chipquik.
Brilliant stuff if you follow the instructions.  They do free samples, so if
you're frugal with it, a free sample will last a long time!

 

There you go, I hope there's something in the above that is of help to you.

 

73  DaveL  G3TJP

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[K2QI]

Thanks for the Chipquick suggestion; will get some of that post-haste.

As for the resistor, I took a look at it again.  Doesn't look as bad as I
thought, and after testing it again with my vom, the reading is actually
13.04k, not 13.4 as I had originally written.  That's less than .05%
variance in tolerance.  Perhaps I will leave it for now... that is unless
anyone else from the reflector cares to chime in and suggest otherwise.

73 de James K2QI



On Thu, Jan 7, 2010 at 8:18 AM, David Lankshear <[hidden email]> wrote:

>  I build a lot of equipment and would never ever trust a damaged
> component.  Don't worry too much about it now, though.  Get your free sample
> of Chipquick and follow the instructions, INCLUDING using the supplied
> liquid flux and a cotton bud you'll steal from the XYL..  All you then need
> to do is melt a small blob of Chipquick over one end of the resistor and
> then go to the other end with your iron, melt the solder and push the
> damaged chip off the pads.  Clean up with cotton buds and flux and you'll
> have pads like new.  Then attach the leaded resistor and hey presto, all's
> comfortable and you can sleep again!
>
> Believe me, Chipquik is great stuff and so is the flux as it stops the
> molten chipquik fro "plating" your PCB.  Don't worry though, a bit of flux,
> heat and a cotton bud is all you need to tidy up.  I reckon a free sample of
> Chipquik lasts me around a year and I use the soldering iron quite a lot.  A
> kind friend got me a second free sample, but I'm going to have to bite the
> bullet soon and order some from the States.  I wish it, and stuff like
> DeoxIT Gold, was stocked by the likes of Mouser, because it's always the
> cost of shipping that spoils the deal for us who don't live in the bottom 48
> HI!
>
> 73  Dave, G3TJP
>
>
>

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