I have some quick, 1 hour, two part epoxy here made for PC use.
I just finished making up a multi order HF band pass filter for one of
my ham radio bands. A friend wants me to make one up and send it to
him too. I'm leary of this because I used toroid cores. During
shipping, I can imagine them coming detached or otherwise losing their
tuning because the windings move around from the bouncing around
during transit. I have some quick, 1 hour, two part epoxy here made
for PC use. Could I carefully "paint" each toroid, windings and some
epoxy between toroid and circuit board so it also won't move? Need a
quick, easy, and effective solution. I wouldn't think the clear, two
part epoxy would affect Q or tuning, or would it?
Thank you!
I just finished making up a multi order HF band pass filter for one of
my ham radio bands. A friend wants me to make one up and send it to him
too. I'm leary of this because I used toroid cores. During shipping, I
can imagine them coming detached or otherwise losing their tuning
because the windings move around from the bouncing around during
transit. I have some quick, 1 hour, two part epoxy here made for PC
use. Could I carefully "paint" each toroid, windings and some epoxy
between toroid and circuit board so it also won't move? Need a quick,
easy, and effective solution. I wouldn't think the clear, two part
epoxy would affect Q or tuning, or would it?
Thank you!
On Thu, 10 Feb 2022 04:54:15 -0500, Jake T <jaketbone@steak.com>
wrote:
I just finished making up a multi order HF band pass filter for one of
my ham radio bands. A friend wants me to make one up and send it to him
too. I'm leary of this because I used toroid cores. During shipping, I
can imagine them coming detached or otherwise losing their tuning
because the windings move around from the bouncing around during
transit. I have some quick, 1 hour, two part epoxy here made for PC
use. Could I carefully "paint" each toroid, windings and some epoxy
between toroid and circuit board so it also won't move? Need a quick,
easy, and effective solution. I wouldn't think the clear, two part
epoxy would affect Q or tuning, or would it?
Thank you!
If your toroidal inductors are wound that loose, you'll have damage in shipping, mostly from the enamel coating falling off from vibration.
Some kind of conformal coating will help. <https://www.chemtronics.com/the-ultimate-guide-to-conformal-coating>
Before selecting any coating, lookup the loss tangent values and see
if it will get hot due to RF losses. If you're not sure, coat a PCB
with the coating, let it dry, and bake it in a microwave oven. If it
tends to crumble, burn, melt, or otherwise self destruct, find
something with less loss. 1kW at 2.4GHz is a rather brutal test for a coating that only needs to work up to 30MHz, but is quick and easy. If
it survives at 2.4GHz, it will work at 30MHz.
If the BP filter is designed using high Q inductors and mechanical
vibration detunes these inductors, your design is faulty and you will
have other problems, such as multiple problems caused by water. I
used to design marine radios and quickly learned that high-impedances,
high-Q tuned circuits, and high voltages were really bad ideas in a
marine environment. So, we designed most everything using low
impedances, low-Q tuned circuits, and low voltages. The result was
that the radio worked nicely when wet and did not require any kind of coating. Such coatings are a mess to apply and handle. Rework is
either difficult or impossible.
Here's an example from about 1980. This is the Intech Inc Mariner
3600 150w PEP SSB HF marine radio: <https://ce3dr.files.wordpress.com/2016/12/img_1630.jpg> <https://ce3dr.files.wordpress.com/2016/12/img_1631.jpg> <https://ce3dr.files.wordpress.com/2016/12/img_1632.jpg> <https://www.hellocq.net/forum/read.php?tid=226493>
The large board full of toroidal inductors are the TX/RX LP (low pass) filters. We didn't use or need BP (band pass) filters. Notice the
lack of any conformal coating. I will admit that we did use some wax
to keep the synthesizer VCO from becoming microphonic. It was also
one of the few circuits that were sensitive to moisture.
Good luck.
Thanks for the info. I should have mentioned that this was for a
receiver and will never be used for a transmitter. I ended up making
the poly glue myself using white foam dissolved in acetone. Works fine.
Took about 8 hours to fully dry. Very sold result and non-conductive.
On Sun, 13 Feb 2022 07:55:55 -0500, Jake T <jaketbone@steak.com>
wrote:
(chomp)
Thanks for the info. I should have mentioned that this was for a
receiver and will never be used for a transmitter. I ended up making
the poly glue myself using white foam dissolved in acetone. Works fine.
Took about 8 hours to fully dry. Very sold result and non-conductive.
You may have goofed. If you are using enamel, lacquer or shellac
insulated copper "magnet" wire for winding your coils, the acetone
solvent will dissolve the insulation. I suspect the reason you
observed a "solid result" is because the "melting" insulation has now
glued itself to the insulation on adjacent turns. That's pretty good
if you can keep it from moving, but since dissolving the insulation
also makes it thinner, I suspect that any movement will cause
intermittent shorted turns.
Hint: Check a chemical resistance chart for whatever you're using for insulated wire before using any solvents:
"Enameled Wire Insulation Characteristics" <https://mwswire.com/insulation-characteristics/>
Before wave soldering machines switched from using chlorinated
hydrocarbon solvents to clean off solder flux (about 1974), to aqueous (water) based cleaning solutions, we used to use vapor degreasers
loaded with trichlorethylene solvent to clean PCB (printed circuit
boards), which included the boards full of PE (plain enamel) magnet
wire wound torroidal inductors (as shown in the M3600 photos I
previously linked). We had to use a special insulated magnet wire AND
keep the temperature very low in the vapor degreaser, in order to not
soften the insulation. We also had to learn not to touch the coils
until the PCB was dry and at room temperature. Polyurethane based insulations were better but still required some care.
Good luck.
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