The classic DIY test of material for RF use is give it 60 seconds in a microwave oven. If it gets warm, its not a good candidate.
The other more typical concern with "RTV" type materials are the ones using acetic acid to cure. This outgases, condenses with water vapor to form an corrosive material on the electronics inside a "sealed" environment. When the unit mails, and you look inside, you find lots of "green" corrosion inside, to the point interconnects fail. There are electronic friendly forms of the sealant that do not have the vinegar odor. Lester B Veenstra MØYCM K1YCM W8YCM [email protected] US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.336826 N 78.982287 W (Google) GPS: 39.33682 N 78.9823741 W (GPSDO) Telephones: Home: +1-304-289-6057 US cell +1-304-790-9192 UK cell +44-(0)7849-248-749 Guam Cell: +1-671-929-8141 Jamaica: +1-876-456-8898 This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Jim Lux Sent: Monday, April 14, 2014 11:32 PM To: [email protected] Subject: Re: [time-nuts] GPS antenna in silicon/RTV encapsulation On 4/14/14, 12:11 PM, [email protected] wrote: > Am experimenting with small low cost GPS antennas and am considering > as an alternative RTV/silicon. Any information on RF attenuation of > RTV/silicon at 1.6 GHz ? > Are you potting the antenna in a solid mass of silicone? Or using it to seal an enclosure or what? pure silicone is very low loss, and it probably has an epsilon around 3. It can be loaded with silica (which is also low loss) to adjust the mechanical properties and electrical properties. It can also be loaded with other things (TiO2) which will increase the epsilon, but also the loss. the plastics that are notorious for loss are ones that have metal or carbon loading or that are hygroscopic so they pick up water. In the clear plastics world, Polypropylene, polyethylene and polystrene are pretty good. Polycarbonate isn't as good, neither are various acetals (Delrin) and acetates Here's a chart http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.h tm or another chart http://www.eccosorb.com/Collateral/Documents/English-US/dielectric-chart.pdf here's a whole report from Dow on silcone rubbers as dielectrics http://www.dtic.mil/dtic/tr/fulltext/u2/656331.pdf They give quite low loss tangents at 10^9 cps (which I looked up on my cps to Hz conversion chart.. That's in your frequency range) 0.0059 loss tangent for Silastic 80. The trick for you will be knowing what else is in your particular silicone resin, and controlling the water content. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
