WARNING! WARNING! WARNING! (was ESD recommendation)

[Don Wilhelm-4]

Stephen,

There is a lot of ripple in the variable filter passband when it is set
to a wide filter value.  Even with the ripple, the filter is quite
usable on SSB voice, but for data modes, it does have its shortcomings.

That is one good reason that I set up the RTTY filter set for use on
data modes.  I typically set the FL1 position the same as SSB FL1 (with
the OP1 SSB filter), but I set relatively narrow widths for RTTY FL2, 3
and 4 - I like to use 1.00 for FL2, 0.70 for FL3 and 0.40 for FL4.  I
center these filters at 1000 Hz (or 800 if the BFO range is not adequate).

In use, you can first tune in the desired signal using the FL1 position,
and then use the VFO to position that signal in the waterfall to 1000
Hz.  You can operate with FL1 as long as no interfering signals come
along - should an interfering signal occur, you can lock the transmit
frequency in the software application and then use the XFIL button to
narrow your receive passband down to a point where the interference is
reduced.  Locking the transmit frequency is required because of slight
differences in the BFO frequency as you shift between the filters - if
you need to retune the receiver frequency (in the waterfall), it will
not change the transmit frequency.

73,
Don W3FPR

Stephen Prior wrote:

> I didn't build my K2 (I wish had!), so I have limited experience of its
> alignment.
>
> Having finally got around to getting back on psk31, I have noticed a banding
> effect in the waterfall - both with mixw on the pc and cocoamodem on the
> mac.  Removing the audio feed from the K2 shows the usual digital artifacts
> often observed with integrated soundcards in particular, but no evidence of
> any ripple.  I'm using the inbuilt sound on a new Intel mac mini running
> both Leopard and XP.  I don't believe the computer is to blame. Anyway, as
> noted below, the OP1 filter shows none of this.
>
> Running spectrogram with random noise at the antenna (not much else on 12m,
> four hours after dark!), I can see a distinct ripple in the passband of all
> filter widths, in every mode.  Except, that the OP1 filter in the ssb board
> gives a flat response in all modes. So it's something to do I guess with the
> setup of the variable crystal filter. I am wondering how far back I will
> need to go in the setting up of the K2 to find the adjustment which will
> perhaps flatten the shape.
>
> Using spectrogram (latest) with the xtal filter in usb at 2.1kHz, there is
> about 10dB between peak and trough of the ripple.  The peaks are roughly
> 600Hz apart.  I'd never noticed this in casual listening, I doubt that I
> could have done.  Most of the time I am on cw and the 700Hz filter setting
> shows no obvious ripple anyway.  It does however certainly not look right on
> the waterfall on psk31!
>
> I'd be grateful for any advice!
>
> Thanks,
>
> Stephen G4SJP
>
>
>
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>  

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[dave.wilburn]

Keep in mind, that it is expected that many of the items that you are
talking about, are being plugged into GFI outlets, which is everything
outside, in garage, in bathroom and kitchen.  Not justifying anything,
just making an observation.
-  

David Wilburn
[hidden email]
K4DGW
K2 S/N 5982


On Sun, 2007-11-25 at 16:45 -0800, Ron D'Eau Claire wrote:

> Has anyone noticed how little that "safety ground" is used by commercial
> products these days?
>
> Few, if any, household appliances such as vacuum cleaners or even kitchen
> appliances use it now. They all have two-wire plugs. For outdoor use I have
> a electric chain saw, and electric circular saw, an electric weed-whacker,
> an electric lawn mower and an electric hedge trimmer NONE of which use a
> 3-wire cord. They were all purchased in the last five years.
>
> All of these devices revert to the standards of the 1940's and 50's, relying
> on insulation without a "safety ground" tied to a metal enclosure. The
> insulation is probably better than was used in the old gear, but it's the
> same old design.
>
> Most of these devices have a polarized plug. The wide spade on the US plug
> is the neutral or grounded side of the mains circuit. Presumably (I haven't
> opened any of them up) they are wired so that a likely short to the metal
> parts would be on that side of the mains. That's also how it was done in the
> 1940's and 50's.
>
> Sure, I check to make sure the safety ground is attached to my household
> outlets. It's astonishing how many outlets I've encountered over the years,
> even in new homes, have no ground connection to the third pin. And many more
> are wired backwards so if one puts a polarized plug in the outlet the wrong
> (hot) side of the mains goes to the normally grounded side.
>
> Frankly, I pay at least as much attention to the correct wiring of the mains
> plug to put neutral on the wide spade as I do about the ground lead being
> connected.
>
> A little three-light tester available at most hardware stores for a few
> dollars is well worth the investment.
>
> Ron AC7AC
>
>
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[Ken Kopp]

In Canada it's not unusual to see rural distribution lines
that have only one conductor on the poles. They use
"earth" for the other half  of the circuit, as in old US rural
phone lines.

Ken K0PP

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[Don Wilhelm-4]

Ron,
On all of the modern 2 wire appliances that I have, there is no exposed
metal - it is all plastic or otherwise insulated.
There was an appliance designation that is termed "Double Insulated"
that used to be in common use. Double Insulated devices depend on the
fact that you cannot touch any part the can connect ot the electrical
circuits, even under fault conditions, and no 3rd ground wire is
required for them.
The equipment of the 40s and 50s often used metal cases that were
connected to nothing - until a fault occurred.  I used to have some of
those old drills that produced quite a 'tickle' when operated outside or
if slightly damp.  That was when I was much younger, and I sometimes
wonder how I survived, but am glad I did.
73,
Don W3FPR

Ron D'Eau Claire wrote:

> Has anyone noticed how little that "safety ground" is used by commercial
> products these days?
>
> Few, if any, household appliances such as vacuum cleaners or even kitchen
> appliances use it now. They all have two-wire plugs. For outdoor use I have
> a electric chain saw, and electric circular saw, an electric weed-whacker,
> an electric lawn mower and an electric hedge trimmer NONE of which use a
> 3-wire cord. They were all purchased in the last five years.
>
> All of these devices revert to the standards of the 1940's and 50's, relying
> on insulation without a "safety ground" tied to a metal enclosure. The
> insulation is probably better than was used in the old gear, but it's the
> same old design.
>
>  

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[AC7AC]

CONTENTS DELETED

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[AC7AC]

CONTENTS DELETED

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[Darrell Bellerive-2]

I took a slightly different approach. I set two of the filters for acceptable
passband ripple and attenuation and let the bandwidth fall where it may. I
did this for CW, but a similar approach would work for data.

Since the actual bandwidth and the indicated bandwidth of the variable filter
can differ quite a bit, I did not see the point of picking an arbitrary value
for the bandwidth. Rather I set the widest filter where the ripple started to
look fairly flat and the narrowest filter where filter loss became more
noticeable.

My filters are centred on 589 Hz which is the pitch of the sidetone when set
to 580 Hz. My sidetone circuit has been modified considerably, and that may
account for the 9 Hz difference between the setting and the measured result.

An audio spectrum analyzer and wideband noise source are required to see the
passband of the filters.

So here's the result:
XFIL 1 - OP1
XFIL 2 - Widest bandwidth where ripple begins to look acceptable. This is
subjective as to what you are willing to tolerate with respect to ripple. My
filter ended up at 970 Hz bandwidth indicated and 512 Hz measured at the -6
dB points
XFIL 3 - Set about half way between XFIL 2 and XFIL 4. Nice smooth passband
and no attenuation. Indicated bandwidth was 600 Hz, with actual -6 dB
bandwidth of 307 Hz.
XFIL 4 - Set at the point where the attenuation began to be quite noticeable.
Indicated bandwidth of 200 Hz and actual measured bandwidth of 178 Hz.

Of course there will be a bit of variation in the actual bandwidth vs the
indicated bandwidth between individual K2s due to component tolerances and
construction differences.

73,
Darrell
VA7TO   K2 #5093




On Sunday 25 November 2007 17:03, Don Wilhelm wrote:

> There is a lot of ripple in the variable filter passband when it is set
> to a wide filter value.  Even with the ripple, the filter is quite
> usable on SSB voice, but for data modes, it does have its shortcomings.
>
> That is one good reason that I set up the RTTY filter set for use on
> data modes.  I typically set the FL1 position the same as SSB FL1 (with
> the OP1 SSB filter), but I set relatively narrow widths for RTTY FL2, 3
> and 4 - I like to use 1.00 for FL2, 0.70 for FL3 and 0.40 for FL4.  I
> center these filters at 1000 Hz (or 800 if the BFO range is not adequate).
>
> 73,
> Don W3FPR
>
> Stephen Prior wrote:
> > Running spectrogram with random noise at the antenna (not much else on
> > 12m, four hours after dark!), I can see a distinct ripple in the passband
> > of all filter widths, in every mode.  Except, that the OP1 filter in the
> > ssb board gives a flat response in all modes. So it's something to do I
> > guess with the setup of the variable crystal filter. I am wondering how
> > far back I will need to go in the setting up of the K2 to find the
> > adjustment which will perhaps flatten the shape.
> >
> > Using spectrogram (latest) with the xtal filter in usb at 2.1kHz, there
> > is about 10dB between peak and trough of the ripple.  The peaks are
> > roughly 600Hz apart.  I'd never noticed this in casual listening, I doubt
> > that I could have done.  Most of the time I am on cw and the 700Hz filter
> > setting shows no obvious ripple anyway.  It does however certainly not
> > look right on the waterfall on psk31!

--
Darrell Bellerive
Amateur Radio Stations VA7TO and VE7CLA
Grand Forks, British Columbia, Canada
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[michael taylor-3]

On Nov 25, 2007 3:20 PM, Ken Kopp <[hidden email]> wrote:
> My older home .... built in 1962 by an individual for
> himself ... has only 2-wire Romex.  At least it's not
,,,
> It's a 2-story structure and it's virtually impossible to
> rewire to meet present-day electrical codes without
> tearing off the interior wallboard and starting over.
...

You can replace non-grounded receptacle with grounding-type (3 prong)
GFCI receptacle according to NEC as I understand it (I am NOT an
electrician). I believe the outlets should be labeled as "No Equipment
Ground."

-Michael, VE3TIX
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[gm3sek]

David Woolley wrote:
>In IEE terms, the PME system is TN-C-S.  The older system is TN-S.
>There is a rare configuation (TT), used for rural overhead supplies,
>where each house has its own earth electrode, but these are not
>connected to the neutral, which is only earthed at the sub-station.

TT is closest to the US system, but "rare" is a misleading word. Of
course the large majority of UK homes are in urban and suburban areas,
where the other two systems predominate. But if you happen to *be* in a
rural area, TT is everywhere.

> For TT systems, RCDs are mandatory.

Yes, because an individual home ground may not be low-resistance enough
to trip the circuit breakers on a short. A typical UK TT system has a
100mA RCD on the whole installation, but the power circuits (wall
outlets etc) are protected by a more sensitive 30mA RCD. This is to
allow the power RCD to trip without disconnecting the house lights.


Returning to the topic of ESD, my Weller TCP is provided with a long
fly-lead and a crocodile clip for equipment grounding. That lead
connects to the ground pin of the 3-pole 24V AC plug, which is in turn
connected to the mains ground. The clip is attached either to the
equipment chassis or, when working on an isolated board, to the board's
own circuit ground. The iron tip and the item being soldered are then
bonded together.

They are also both bonded with a low resistance to the mains ground, but
that is OK. Seems to me that the series resistors are meant for any
*other* large items that could pick up a significant static charge -
mainly the human operator and the bench mat.

A circuit board is not physically big enough to pick up a significant
charge in its own right. The main hazard to circuit boards is when a big
static charge is made to pass *through* the vulnerable parts on the
board. There are three main scenarios where this can happen:

1. If the board is already grounded and the iron tip is not - the
fly-lead prevents that one; or

2. If the board is already grounded, and an ungrounded operator touches
a vulnerable pin (well, don't do that  - be grounded first, through a
resistor wrist strap, and always pick up boards by their edges); or

3. When the ungrounded operator picks up the board, and then grounds
himself *through* some vulnerable part of the board (well, don't do that
either - be grounded first, through a resistor wrist strap; and make
sure the equipment is grounded too).



--

73 from Ian GM3SEK         'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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