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Hi Steve,

You can't measure many of the square waves created in this
radio with a 100MHz scope, and expect them to look at all
like a square wave.

A square wave is comprised of odd harmonics of the fundamental
frequency, at say, 30 MHz, your scope could see the fundamental,
and the 3rd harmonic, but would be pretty blind to the 5th.

Also, the usual 6 inch ground wire on the usual 100MHz probe
will be adding in a whole lot of distortion to any signal you
are measuring.

As a good rule of thumb, your scope should have at least 10x
the bandwidth of the non sinusoidal signal you wish to measure.

Your probe's ground wire should be at most 1 inch long.

-Chuck Harris, WA3UQV


On Wed, 26 Mar 2025 12:12:32 -0700 "Steve N2IC via groups.io"
<n2icarrl@...> wrote:

Thanks, Stan,

I'm going through all this effort before ordering parts because it
was quite a destructive event. One of the BS170's was physically
broken, and the board under it charred.

My scope is an old HP 1740A, 100 MHz. I changed probes, and now the
input side of IC502 looks like a good square wave. However, the
inputs and outputs of IC503C/D are not clean.? IC503A/B look okay.
I'm betting that IC503 was damaged.

Now I'm looking at Q507. I? have read Ludwig's postings on this. With
all the BS170's removed, the Diagnostics screen shows the transmitter
voltage at 10.9 volts. Ludwig says it should be close to 0 volts, but
maybe that is with good BS170's. The two SMPS look fine.

73,
Steve, N2IC

Stan,

I scoured my post for a personal attack, and could not find
one.

Motor wire is an exotic wire when used in a QRP radio kit.

Compact, intermittent duty, motors quite often are built to
withstand short term very hot operation... often thermally
stressing even 200C rated wire.

These kits are low temperature, low power radios, that come
provisioned with a thermal stripping wire, equivalent to
thermaleze.

A large quantity (2x the total amount required) of the desired
wire was included with each kit. Easily enough to cover the
occasional oops an inexperienced builder may encounter.

Your use of high temperature motor wire, to replace the wire
that comes with these kits, makes your choice an outlier for
the overwhelming majority of builders of these kits.

It appears to me that its principal benefit is that *you*
had it on hand.

An inexperienced builder will find it challenging to use a
knife to completely strip a #28AWG wire without damaging,
or incompletely stripping, the wire.

I find that most inexperienced craftsmen greatly over
estimate the forces required to do fine operations. They
also greatly underestimate the time required to do fine
operations properly. Either can cause disappointing results.

Sanding off wire insulation has its own difficulties. Most
high temperature motor wire insulation is also designed to
protect against abrasion... which is exactly what you are
trying to do when you sand or scrape the insulation off of
the wire. The insulation is almost always tougher than the
copper wire itself, causing the side where you first break
through to the copper to get sanded much more quickly than
the rest of the wire. By the time your are done, the wire
will be in the shape of a flat oval.

If everyone was using, or could be reasonably expected to be
using, high temperature, non-thermal stripping wire on their
kits, then your advice would be spot on.

I believe they are not, but are rather seeing the heat
sinking effect of the large continuous ground planes needed
for high quality RF work. Through the use of poor technique,
or perhaps ineffective soldering equipment, they are not
getting enough heat into the joint to melt (not burn) the
usually easy to strip thermaleze style wire.

A simple match, or a lighter, to pre-strip the wire will help
with that job, and not put the wire at much risk.

-Chuck Harris, WA3UQV


On Wed, 26 Mar 2025 09:52:57 -0700 "Stan Dye via groups.io"
<standye@...> wrote:

On Tue, Mar 25, 2025 at 09:11 PM, Chuck Harris wrote:

if you use something exotic, such as a
ceramic insulated wire, my tip about using a common lighter
won't work.

You may not know it, so I will help you: You are using an
exotic wire.

Please avoid using personal attacks, Chuck.
Some facts:
1- I can assure you again that I am not using exotic wire.
It is this:

It turns out that you can buy inexpensive wire that has has high
temperature enamel.? It is made for motor windings. It certainly is
not ideal for winding toroids for qrp.? And the enamel will NOT burn
off with a simple lighter.? Get some. Try it. Or not. But I have it,
and I have used it for winding toroids for ATU kits and transformers.
2- I do use the kit wire supplied by qrp-labs for my qrp-labs kits.
The smaller diameter wire provided will indeed burn off with
soldering or a lighter - it is of a thermaleze type. 3- For the older
kits with the .6mm wire, here is a quote from Hans' transformer
winding doc: "If using 0.60mm wire, scrape the wire enamel from this
1cm section. The enamel on the 0.60mm wire will be very difficult to
remove using heat; so it is better to scrape it or sand it." 4- I
agree with Hans.? I don't think that wire had a thermaleze type
insulation, either. 5- I, too, have recently retired from a 40+ year
career of electrical engineering design/build/test.? I'm not an
expert with RF circuits, but I do know my wire and how to use it.
Stan KC7XE

OR...one could switch to their trusty Yaesu FT-450D, as I do, during antenna "tuning" :0)
72,
Bill, N4QA/4/QRP Oak Island ( OKI ), North Carolina, U.S.A.