Sorry about the off topic post, but can anyone suggest a source of Litz wire that can be used outside in the weather.[PVC, or Teflon, etc covered]. I`m going to build a loop antenna for receive, and need several meters. Thankyou!? <donaldbcollie@...>

On 12/4/20 2:50 AM, donald collie wrote:

Thanks for the suggestion George - there`s plenty of cotton covered
stuff on eBay [bless em]...................Don C.

<>
????Virus-free. www.avast.com
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On Fri, Dec 4, 2020 at 6:08 PM george edmonds via groups.io
<> <G6HIG@...
<mailto:[email protected]>> wrote:

??? Donald

??? I would suggest that you use standard cotton covered and put
??? several layers of varnish on it.

??? George G6HIG Dover UK
??? On Friday, 4 December 2020, 00:21:54 GMT, donald collie
??? <donaldbcollie@... <mailto:donaldbcollie@...>> wrote:


??? Sorry about the off topic post, but can anyone suggest a source of
??? Litz wire that can be used outside in the weather.[PVC, or Teflon,
??? etc covered]. I`m going to build a loop antenna for receive, and
??? need several meters. Thankyou!? <donaldbcollie@...
??? <mailto:donaldbcollie@...>>

I may be missing something, but "standard cotton-covered wire" with
"several layers of varnish" does
not appear to me any better than standard magnet wire, with its own
insulating varnish, and a lot
less trouble.
--doug, WA2SAY--retired RF engineer

Hi Rainer. I`m planning a 10 turn square loop, with turns spaced an inch or so to get the self resonant frequency to be as high as possible. Each side will be 2meters or so long, so I`ll need 2 x 4 x 10 meters, or 80 meters total.? I`m not using a screened loop, because the turns would be close to each other, and the self capacitance would be higher, causing the self resonant frequency to be lower. Thanks for your response......................Don Collie

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Depending on the frequency, PVC's loss tangent will ruin your loop Q, so try to use
HDPE or LDPE instead.

Possible source of litz wire can be transformers used in high efficiency SMPS's, but
the ideal litz wire (wire thickness and qty of wires) changes, even across the MW band.

If you want to build a kick-arse receive loop for MW, I highly recommend the late
Graham Maynard's "Sprial loop with Q multiplier" as found in Practical Wireless - the
best loop I've ever used (feeding into a Racal RA17L).

Ordinary PVC is very, very low loss through low microwave frequencies, as is
easily demonstrated by putting a piece in your microwave oven.
Do you have a reference I can look at that shows your assertion?
-Chuck Harris
Andy ZL3AG via groups.io wrote:

Depending on the frequency, PVC's loss tangent will ruin your loop Q, so try to use
HDPE or LDPE instead.

Possible source of litz wire can be transformers used in high efficiency SMPS's, but
the ideal litz wire (wire thickness and qty of wires) changes, even across the MW band.

If you want to build a kick-arse receive loop for MW, I highly recommend the late
Graham Maynard's "Sprial loop with Q multiplier" as found in Practical Wireless - the
best loop I've ever used (feeding into a Racal RA17L).

For a comparison of PVC versus PE (HDPE is just as good), the best source of
dielectric loss mesurements is Von Hipples work from MIT, around WWII. Since you may
not have his text book, can download the data from "Tables of Dielectric Materials"
from DTIC.MIL, I think that's the Defense Technical Info Center. Google it, and Von
Hipples name. Once you downloaded the PDF, look at page 116 for polyvinyl Chloride
and page 153 for polyethylene. Dielectric constants for both are relatively similar.
But look at loss tangent. At 1 MHz PVC is 0.016, PE is 0.0002. And you can see
similar difference up to 10^7 (10 MHz) and 10^8 Hz. In RF heating (which is the
effect that loss give), the loss tangent is directly related as is frequency.
Electric field is a squared term. I would not recommend PVC insulation on anything
that has high RF voltage in the MHz, unless you don't mind the loss and the part is
cooled. Using PVC pieces as spiders for an open wire RF transmission line that is
matched is probably OK, but not in a resonant circuit where the electric field rises.
So it depends on the application. PVC is a very polar molecule like water, having a
net dipole moment. These little dipoles are what causes the loss. Don't forget that a
microwave oven at 2450 MHz has a low field strength as it is not a single resonant
mode, in fact the fields are bouncing all around. When I worked for DuPont years ago,
I was in the dielectric heating group. We would get chemists all the time saying
"this stuff is great, I put in in my microwave oven and it only warmed in xx
minutes." To which we would open the cover of our 90 Mhz WT LaRose heater with about
15 kV across the plates, and the PVC would catch on fire in 10-20 seconds. Believe
me, I have done this dozens of times to prove out various hose and insulation
materials in high power RF amplifiers in my workplace.