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desoldering stations and RF.

J

Jamie

Jan 1, 1970
0
At one my work stations where I put together small prototypes
I finally discovered why the desoldering vacuums wand needs to
be set higher in temp. I just wrote it off as a defective sensing
circuit in the station because I tried another wand on it. However,
the other day, I found out what was causing the defected reading and
throwing off the controller..

R.F. around it causes the thermo coupling circuit to register higher
readings and forces the controller to throttle back. My guess is it may
have something to do with the ring near the tip that handles the seebeck
circuit.

The R.F. source is a repeater in the 440Mhz range near by, just over
my head. Lately, it has been very active in our locality.

I will need to investigate more, the type of input it is using.
Something tells me it could be monolithic in nature and the front
end maybe rectifying the signal?

Jamie
 
S

Spehro Pefhany

Jan 1, 1970
0
At one my work stations where I put together small prototypes
I finally discovered why the desoldering vacuums wand needs to
be set higher in temp. I just wrote it off as a defective sensing
circuit in the station because I tried another wand on it. However,
the other day, I found out what was causing the defected reading and
throwing off the controller..

R.F. around it causes the thermo coupling circuit to register higher
readings and forces the controller to throttle back. My guess is it may
have something to do with the ring near the tip that handles the seebeck
circuit.

The R.F. source is a repeater in the 440Mhz range near by, just over
my head. Lately, it has been very active in our locality.

I will need to investigate more, the type of input it is using.
Something tells me it could be monolithic in nature and the front
end maybe rectifying the signal?

Jamie

Probably right on. Bipolar op-amps are notorious for rectifying RF
signals and converting it to a some uV of DC. 20 degrees C on a type K
thermocouple would be around 850uV. It can usually be reduced to a uV
or two with careful filtering and design of the input circuit, but I
suspect solder stations have the goodness Muntzed out of them to save
a few pennies on ceramic caps and such like.


Best regards,
Spehro Pefhany
 
P

Pimpom

Jan 1, 1970
0
Spehro Pefhany said:
Probably right on. Bipolar op-amps are notorious for rectifying
RF
signals and converting it to a some uV of DC.

Discrete low-power AF stages are also prone to that effect. In my
town (NE India), the P.A. system in some churches have
experienced serious interference from the local AM transmitter,
particularly in the past when many churches could afford only
cheap PA sets, most of them installed by local youth. It doesn't
seem quite appropriate to have the pastor deliver a sermon to the
accompaniment of GnR or Lady Gaga. The solution I came up with
was to insert an LPF or an LC circuit tuned to the AM station
between the mic jack and the amplifier input. Some churches in
certain rural areas are also complaining about inteference from
Chinese and Bangladesh stations.
 
T

Tim Williams

Jan 1, 1970
0
John Larkin said:
I was RF testing this controller and found some sharp resonant
responses in the 150 MHz sort of range. We plucked this core out of a
Fair-Rite sample kit and popped it in, and it improved things roughly
30 dB. True, it's probably not a deliberately lossy ferrite, but it
sure works.

I don't know that it's actually ohmic loss that's helping... maybe
it's just the series inductance.

Those are most often type #43, which has reasonable permeability up to a few
megs, but a fairly broad resistive band out into 100-200MHz. Same material
is typically used for "medium frequency" EMI parts.

Tim
 
T

Tim Williams

Jan 1, 1970
0
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