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Epoxy & microwaves?

D

DaveC

Jan 1, 1970
0
Building a DIY antenna for 2.4 GHz. Need to support elements and bond
components together.

Are common epoxies non-absorbing at this wavelength?

Thanks,
--
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ask a question here if I hadn't done that already.

DaveC
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R

roby

Jan 1, 1970
0
DaveC said:
Building a DIY antenna for 2.4 GHz. Need to support elements and bond
components together.

Are common epoxies non-absorbing at this wavelength?

Thanks,

Put a sample into the epoxy tester in your kitchen, along with a glass
of water to provide some load.

If the sample gets hot or melts, it is an absorber.

Roby
 
J

John Popelish

Jan 1, 1970
0
DaveC said:
Building a DIY antenna for 2.4 GHz. Need to support elements and bond
components together.

Are common epoxies non-absorbing at this wavelength?

Cure some and put it in the microwave oven and see how fast it gets
hot compared to an equal volume of water.
 
M

Mac

Jan 1, 1970
0
Building a DIY antenna for 2.4 GHz. Need to support elements and bond
components together.

Are common epoxies non-absorbing at this wavelength?

Thanks,

Yes they are (relatively) non-absorbing.

Just think about it: FR4 is made using epoxy resin, and 2.4 GHz
signals travel a fair way in FR4 without too much attenuation.

If in doubt, you could irradiate a batch in the uWave oven, as others have
suggested.

If you (or another member of your household) is opposed to putting cured
epoxy in the oven, you could try asking the technical support
people at the company who makes the resin.

--Mac
 
Z

Zak

Jan 1, 1970
0
DaveC said:
Building a DIY antenna for 2.4 GHz. Need to support elements and bond
components together.

Are common epoxies non-absorbing at this wavelength?

Well, if you build a yagi, there is no voltage where the elements cross
the boom. It does not matter what you use there (insulator, conductor)
as long as it is small.


Thomas
 
D

DaveC

Jan 1, 1970
0
Well, if you build a yagi, there is no voltage where the elements cross
the boom. It does not matter what you use there (insulator, conductor)
as long as it is small.

Panel antenna driven by 4 dipoles. Standoffs and epoxy between driven
elements and reflector. Any absorbing material there, I think, will effect
performance.
--
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ask a question here if I hadn't done that already.

DaveC
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J

John Popelish

Jan 1, 1970
0
DaveC said:
Panel antenna driven by 4 dipoles. Standoffs and epoxy between driven
elements and reflector. Any absorbing material there, I think, will effect
performance.

The first thing you have to worry about if there is any dielectric
other than air between elements is how it changes the optimum element
length and spacing, because of the change in the propagation speed of
light.
 
D

DaveC

Jan 1, 1970
0
Panel antenna driven by 4 dipoles. Standoffs and epoxy between driven
The first thing you have to worry about if there is any dielectric
other than air between elements is how it changes the optimum element
length and spacing, because of the change in the propagation speed of
light.

I suspect that the solution gets quite complex. Is there some rule-of-thumb
that can be used? Or possibly support the elements by the ends, minimizing
the dielectric between the elements and reflector?

Thanks,
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
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J

John Popelish

Jan 1, 1970
0
DaveC said:
I suspect that the solution gets quite complex. Is there some rule-of-thumb
that can be used? Or possibly support the elements by the ends, minimizing
the dielectric between the elements and reflector?

Since most of the voltage appears at the ends of antenna elements, you
want to keep supports away from the ends. It would take some test
data (or simulations) to determine how placing elements, say, on the
surface of a circuit board, instead of rods suspended in air would
alter the resonant lengths and optimum spacings.
 
T

**THE-RFI-EMI-GUY**

Jan 1, 1970
0
Dave
It shouldn't be too complex to estimate the element length of an antenna
partially supported in a dielectric.

An engineer at work was assembling a 900 Mhz reference dipole for me. He
did a beautiful job supporting the elements with a hand sawed
polyethylene yoke. All was great until he tuned it up. He could not
find the resonance point where he expected it should have been. It
resonated much lower than expected for the rod length. What I figured
was that the portion of the dipoles which were mounted within the
plastic yoke were influenced by the velocity factor of the polyethelene.
I calculated the percentage of rod length so affected, versus the
portion in freespace and surprisingly was able to pin down that the
resonance was where it belonged for the mechanical length of the
dipoles. We then trimmed the rods down and were satisfied with the
resonance.
I suspect that the solution gets quite complex. Is there some rule-of-thumb
that can be used? Or possibly support the elements by the ends, minimizing
the dielectric between the elements and reflector?

Thanks,

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.
 
T

**THE-RFI-EMI-GUY**

Jan 1, 1970
0
Dave
It shouldn't be too complex to estimate the element length of an antenna
partially supported in a dielectric.

An engineer at work was assembling a 900 Mhz reference dipole for me. He
did a beautiful job supporting the elements with a hand sawed
polyethylene yoke. All was great until he tuned it up. He could not
find the resonance point where he expected it should have been. It
resonated much lower than expected for the rod length. What I figured
was that the portion of the dipoles which were mounted within the
plastic yoke were influenced by the velocity factor of the polyethelene.
I calculated the percentage of rod length so affected, versus the
portion in freespace and surprisingly was able to pin down that the
resonance was where it belonged for the mechanical length of the
dipoles. We then trimmed the rods down and were satisfied with the
resonance.
I suspect that the solution gets quite complex. Is there some rule-of-thumb
that can be used? Or possibly support the elements by the ends, minimizing
the dielectric between the elements and reflector?

Thanks,

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.
 
D

DaveC

Jan 1, 1970
0
I calculated the percentage of rod length so affected, versus the
portion in freespace and surprisingly was able to pin down that the
resonance was where it belonged for the mechanical length of the
dipoles. We then trimmed the rods down and were satisfied with the
resonance.

I was going to ball-park it by supporting only the centers of the rods,
thereby minimizing the impact of the stand-offs. The rods are really short (~
3 cm) so I'm betting that if I support only the center of each rod, they
won't be impacted much.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
[email protected]
This is an invalid return address
Please reply in the news group
 
I

Isaac Wingfield

Jan 1, 1970
0
DaveC said:
I was going to ball-park it by supporting only the centers of the rods,
thereby minimizing the impact of the stand-offs. The rods are really short (~
3 cm) so I'm betting that if I support only the center of each rod, they
won't be impacted much.

Just got into this thread, but checked back along it to the original
question.

I think epoxies are not too good as UHF dielectrics. I know that
standard "green" epoxy-glass circuit board material is not. You might
try "hot-melt" adhesive, especially the milky-clear ones. They are
likely to be polyethylene or a related compound. Polyethylene is used as
the dielectric in many types of coaxial cable, and is pretty decent even
at UHF.

Isaac
 
T

**THE-RFI-EMI-GUY**

Jan 1, 1970
0
Well the shorter they are (IE: UHF/Microwave antenna) the more
significant effect the dielectric support is going to have on the
overall electrical length. What frequency is this antenna?

Joe
I was going to ball-park it by supporting only the centers of the rods,
thereby minimizing the impact of the stand-offs. The rods are really short (~
3 cm) so I'm betting that if I support only the center of each rod, they
won't be impacted much.

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.
 
D

DaveC

Jan 1, 1970
0
It shouldn't be too complex to estimate the element length of an antenna
partially supported in a dielectric.

That's easy; measure.
An engineer at work was assembling a 900 Mhz reference dipole for me. He
did a beautiful job supporting the elements with a hand sawed
polyethylene yoke. All was great until he tuned it up. He could not
find the resonance point where he expected it should have been. It
resonated much lower than expected for the rod length. What I figured
was that the portion of the dipoles which were mounted within the
plastic yoke were influenced by the velocity factor of the polyethelene.

OK, that seems logical.
I calculated the percentage of rod length so affected, versus the
portion in freespace and surprisingly was able to pin down that the
resonance was where it belonged for the mechanical length of the
dipoles. We then trimmed the rods down and were satisfied with the
resonance.

How did you determine how much to trim? By the same percentage that the rods
were supported by the yoke?
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
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D

DaveC

Jan 1, 1970
0
What frequency is this antenna?

2442 MHz, center f. 802.11 wlan.
--
Please, no "Go Google this" replies. I wouldn't
ask a question here if I hadn't done that already.

DaveC
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