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Re: Some thoughts on cases for exterior loop antenna amplifiers
On 8/20/2024 08:56, rfsam wrote:
I was actually thinking about some easy to use spray on UV protectionI can: NOT, NOT, NOT! Recommend the Krylon UV Archival Spray. As applied, it sucks. Fails almost immediately, relatively speaking, maybe a month or two. 8 coats? Still sucks, but fails in a couple years, then the damage to the item begins. I have an item in the yard, saw it just yesterday morning. At least eight coats, noticed fading about two years ago, now, about four years after putting up, item is unidentifiable. Coating failed entirely, UV bleached the item bone white, all I bought was some time, and lost the item. Maybe a 1/8" thick (when dry) layer would do the job, like when I had to pour two one gallon cans of Kilz onto a floor before it actually covered the stain it claimed to- in a single coat, no, wait, three, maybe, they don't seem to know either. Krylon may have a purpose, best as I can tell, it's get get money for a poor product. Good UV resistant cases have the UV protectant mixed in. They may get dusty on the surface, but will hold up for 20+ years. You can generally tell by the uniquely bad chemical smell they give off. Can't describe it, but once you get a whiff, you won't forget. It's very common in outdoor weather stations, so if you have a sensor that's holding up, rub it, then sniff it, see if it smells like toxic waste. Krylon = NO! Kurt |
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Re: Some thoughts on cases for exterior loop antenna amplifiers
Maybe something like
that? Simon On Tue, Aug 20, 2024 at 8:57?AM rfsam via groups.io <1rfsam@...> wrote:
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Re: Some thoughts on cases for exterior loop antenna amplifiers
I was actually thinking about some easy to use spray on UV protection
that I can just use on an amplifier box while it's already mounted on a mast. Could you recommend any sprays like that? Maybe something that can be picked up in a local hardware store or Amazon? Thank you, Simon On Mon, Aug 19, 2024 at 8:08?PM tardivat via groups.io <tardivat@...> wrote:
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Re: Some thoughts on cases for exterior loop antenna amplifiers
Rather than investing considerable money and effort into some super enclosure its? far more effective to coat the loop amplifier PCB in a decent conformal coal lacquer. Conformal coating along with good silicone grease on connections will enable a PCB to survive outdoors with no enclosure.?
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You can get acrylic or silicone conformal coatings. I prefer the brush on thicker coatings for RF work and it stabilises the rf transformers. The dielectric impact is nothing to worry about at HF.
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After this the next best option is fully potting the amplifier with a silicone potting compound designed for electronics.
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The other thing that I have used for electronic enclosures is plastic thermos style flasks. They are insulated and have a waterproof screw cap lid. I have had electronics preamps in these enclosures in minus degree temperature for years without issues especially if sealed where holes are made with modern polyurethane and silicone greases.
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Re: Some thoughts on cases for exterior loop antenna amplifiers
wn4isx
I've used small bore needles to make holes in PVC plastic cases for other projects, a remote reading barometer where one pressure sensor tracks rapid, real time, air pressure changes and the other is inside a smaller plastic container with a very small hole made by a 22 gauge needle, 0.159mm.
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It's part of my "tornado" detector that did sound an alert when a tornado was on the ground about a mile away from where we used to live.
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This has been a long term (50 year) project with a lot of sweat, tears and frustration then I can possibly explain in less then 10,000 words.
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Sorry for the length of this thread, I did not mean to make a mountain of a molehill. I considered CCW's use of a Hylex membrane in their crossed dipole to the right solution to a constant problem I'd had and wanted to share one obvious solution.
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My previous outside active antennas all suffered from major condensation.
My tornado detector draws about 10W and runs warm enough for condensation to not be a problem.
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I've found a few links to serious water condensation issues in advanced electronics, should I continue the research and post it under it's own thread? The problem is links come and go.
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I think I'll go with a small hole and Gortex patch, the patch makes more sense then Gortex repair tape because the patch is designed for the application.
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Re: Some thoughts on cases for exterior loop antenna amplifiers
My experiences.
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Don't have any cables or connectors mounted on the top or sides of the box, fit them on the underside, so that surface water drains away easily, and doesn't "pool" around the connector body.
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Don't bother with lots of gaskets and sealant, as condensation and changes in air pressure will eventually allow moisture to find a way around them, usually via connectors.
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Connectors with screw threads such as 'F' types will allow water to track along the length of the thread. A thin layer of PTFE plumbers tape wound on the thread before the connectors are mated, helps to "seal" the thread from water ingress.
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1mm drain hole on the lowest part of the internal wall works well.
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In more exposed locations, use a box within a larger box, that can act as a solar / weather shield.
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Polycarbonate is best for outdoor use. Other materials suffer from UV, and become discoloured and brittle
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Regards,
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Martin |
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Re: Some thoughts on cases for exterior loop antenna amplifiers
A drain hole can be 1mm in diameter and work fine but drilling a smaller hole can lead to drill breakage. Just drill a small hole 1-2mm diameter. Injection moulded plastic boxes have sloping sides ( draft angle) so that the box cleanly exits the moulds. If a box is mounted vertically then drill holes near the "seal". There is no need at all to cover up the hole. But you do need it at the lowest place in the enclosure.
The daily cycle of heating and cooling from day to night causes the air inside the box to heat and cool so air passes into and out of the box every day. When water condenses inside the box it is expelled when the box warms up. A droplet of water can NEVER block the hole.? A filter does not stop the ingress of water, it can only stop insects but you don't get many insects through a 1mm hole, I've? been putting active antennas outside for over 60 years. Initially I used full epoxy encapsulation then switched to an epoxy? dip of the electronics.? Now I use a spray coat of boards, quicker, much cheaper and easy to rework. In all those years with antennas at many sites I have never lost an antenna through water ingress. But it is very important to stop water entering the coax, the outer screen will corrode causing the crossing conductors to loose contact after a few years. Wrapping the coax and connector with self amalgamating tape that is stretched when applying is a very good sealing method. Sometimes you can spend 99% of effort? thinking about a 0.01% problem. 73, Alan G8LCO |
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Re: Some thoughts on cases for exterior loop antenna amplifiers
Thanks for the reassurance, Simon!
One niggling problem less to fret over :-) Michael 2E0IHW On 19/08/2024 17:46, rfsam wrote: Hi Michael,... Simon Simon, is your hole similar? |
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Re: Schematic & PCB design software
Just another thought on the subject of CAD software selection. I had to find a symbol and footprint of this part not so long ago:
I'd probably go with the software that's listed in SnapEDA selection. In my particular case I had to find a Schematic/Layout symbol for Eagle.
Simon |
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Re: Good Morning from Rural VA
Hi Guy,
Sorry for that. Didn't created a shared link properly. I hope this one will work: Regards, Simon KM6MUL On Mon, Aug 19, 2024 at 7:26?AM Guy Mengel N1GMM via groups.io <guy@...> wrote:
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Re: Some thoughts on cases for exterior loop antenna amplifiers
Hi Michael,
Here is a pic of my CCW Experimenters amp. I'd say this vent hole is about the size of the center pin hole in BNC Female connector. Very close in diameter. Regards, Simon KM6MUL On Mon, Aug 19, 2024 at 2:21?AM Michael.2E0IHW via groups.io <blumu@...> wrote:
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Re: Wellbrook traced-out loop amp schematics uploaded to Photos
The BF862 (obsolete) from NXP is very similar to the 2SK932.? I successfully used it in my Wellbrook built.
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The LT-Spice model:
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.model BF862-13 NJF(Beta=47.800E-3 Betatce=-.5 Rd=.8 Rs=7.5000 Lambda=37.300E-3 Vto=-.57093Vtotc=-2.0000E-3 Is=424.60E-12 Isr=2.995p N=1 Nr=2 Xti=3 Alpha=-1.0000E-3 Vk=59.97 Cgd=7.4002E-12 M=.6015 Pb=.5 Fc=.5 Cgs=8.2890E-1 Kf=87.5E-18 Af=1 mfg=NXP)
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regards
Fred |
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Re: Some thoughts on cases for exterior loop antenna amplifiers
as mentioned bofore, if you are in doubt with a hole only,? just use a Gore adhesive vent pad to cover the hole. These small self adhesive membrane pads are available in various diameters, also for small holes and cost only about 6 USD / 50 Pieces
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regards
Fred |
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Re: Some thoughts on cases for exterior loop antenna amplifiers
wn4isx
On Mon, Aug 19, 2024 at 05:21 AM, Michael.2E0IHW wrote:
I wondered whether too small a hole would allow I mentioned capillary action in an early post, look it up, it is a fascinating subject.
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Liquids will literally be sucked into very small gaps. I suspect, but don't know, a droplet of water would be wicked through a 0.1mm hole with no trouble because water will be wicked up almost a half inch if you place one end of a 0.1mm pippete in distilled water.
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We studied this in physics but it was 50 years ago and, while I was impressed, I didn't pay enough attention because I thought it'd never apply to anything I was interested in.?
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Re: Some thoughts on cases for exterior loop antenna amplifiers
On 8/19/24 11:21 AM, Michael.2E0IHW via groups.io wrote:
I wondered whether too small a hole would allowFolks, you overcomplicate the thing. As Tom advised, drill a tiny hole at the bottom of the plastic case/tube/whatever, install a small bag of desiccant inside and that is all to it. For the size of the drill bit: choose something smaller than the smallest insect you saw. It was 0.6-0.8mm for me, sure enough for the enclosure to breathe and prevents worms to crawl in. This worked for me perfectly. Simon, is your hole similar?Giggling... 73... Sanyi, HA3PG |
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Re: Some thoughts on cases for exterior loop antenna amplifiers
Thanks, Tom!
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I wondered whether too small a hole would allow a droplet to block the hole and defeat its purpose :-) Simon, is your hole similar? 73 Michael 2E0IHW On 18/08/2024 23:58, Tom - VE3PSZ wrote:
I have built about 20 amplifiers for outdoor use. All of them in IP65 type boxes. I always drill a 1/16" (1.5mm) hole in the side facing downward. Some of my units have been outside for 3 years now without a trace of water inside. Tom |
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Re: Schematic & PCB design software
Maybe it will get cheaper...don't bet on it. On Sun, Aug 18, 2024, 11:39 AM Scott Dupuie via <groupsio=[email protected]> wrote:
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Guy Mengel N1GMM
Sam Reaves
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