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Author Topic: Radiant Barrier  (Read 701 times)

K4NYM

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Radiant Barrier
« on: April 14, 2020, 11:37:00 AM »

i lived in an HOA community near Lakeland, FL. I have a single family home on a corner lot. I am not allowed to have any outside antenna, although I am allowed up to a 20' flag pole. I'm considering a flag pole vertical for HF but this will be a first for me. I have no idea where to start. The other option is the attic. The attic is only accessible via a pull down ladder. There is nothing up there except blown insulation and a radiant barrier on the inside of the roof. The barrier is highly reflective aluminum foil used to lower temperatures during the summer. I don't know for sure, but I surmise that the radiant barrier is an RF killer.

I want to ability to work CW and phone on HF and also access local repeaters on 2 meters. I'm open to suggestions and resources that may be able to help.

Thank you.
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KD0REQ

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Re: Radiant Barrier
« Reply #1 on: April 14, 2020, 11:59:06 AM »

mag loop?
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W1VT

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Re: Radiant Barrier
« Reply #2 on: April 14, 2020, 12:03:52 PM »

Put up an antenna and listen.  RF can leak through narrow gaps.  But, a dipole attic may not have much height. 
A vertical normally works better than a low dipole.  Particularly a dipole next to noise generating devices.

I put up a 20 ft flagpole and found it resonant on 30M.  With an automatic tuner at the feedpoint it was usable on 40M through 10 meters. 
I was able to work Japan with 5 watts using the JT65 digital mode using it.  It was harder to work Japan that way than to work them on QRP CW.
With all the folks on FT8 digital it seems easier now to work DX on CW.

Zak W1VT
« Last Edit: April 14, 2020, 12:08:23 PM by W1VT »
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K1VSK

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Re: Radiant Barrier
« Reply #3 on: April 14, 2020, 12:17:18 PM »

You attic also contains all the metal ductwork for AC which will interact with any antenna in close proximity. Regardless, even at VHF, the foil insulation has been proven to severely attenuate signals. A little might “leak” out but just as likely not. At HF, it can be very problematic.

Your best bet is a flagpole vertical which isn’t difficult to construct or you can buy a commercially available one widely advertised which can be a reasonably effective antenna with a proper radial field. Vent pipe antennas attached to stack gas pipes in your roof can also be made which are unnoticeable at VHF.

I’d suggest you contact your local CERT communications group members, many of whom are likely hams who may be able to provide you with their ‘work-arounds’ as well as any exceptions to the local HOA limitations which, in our HOA, exempt CERT members from the antenna exclusions.

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KR6NU

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Re: Radiant Barrier
« Reply #4 on: April 14, 2020, 12:32:41 PM »

Just wondering what type of roofing the house has (cement tile, composition, etc.) and are the walls stucco?
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WY4J

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Re: Radiant Barrier
« Reply #5 on: April 14, 2020, 12:33:06 PM »

I am allowed to put up a 25 foot flagpole so I decided on a 30 foot 10-80 meter flagpole. Nobody noticed the additional 5 feet. and all my neighbors love it. I did place it on the backyard as this made it less accessible/visible from the street and made it easier to lay down 1,500 feet of radials. Is not a directional at 50 feet but it works perfect for my needs. These are the links to a couple of zero-five flagpole.

24 foot 6-40 meters
https://zerofive-antennas.com/productdisplay/24-foot-6-40-meter-high-performance-commercial-duty-flagpole-antenna

20 foot 6-30 meters
https://zerofive-antennas.com/productdisplay/20-foot-6-30-meter-high-performance-commercial-duty-flagpole-antenna
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W6QW

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Re: Radiant Barrier
« Reply #6 on: April 14, 2020, 12:36:12 PM »

I would avoid the attic antenna.  Beyond the foil backed roof sheeting problem, you will find lots of home-grown RFI, both on the RX and TX side on the HF frequencies.  The 20 ft "flagpole" vertical will work just fine.  Just remember that the need for an abundant ground radial field is necessary for any sort of transmission efficiency.  You can even elongate the vertical radiator by adding aluminum MIG wire (0.030" or 0.035") painted with a flat black or camouflage color.  Use the MIG wire as either  an extended top-hat or inverted-L.  The wire is strong enough (I've had stealth antennas using the MIG wire and it only breaks on occasion - most likely from a bird flying into the wire.  Easy enough to replace though.  The painted MIG wire is virtually invisible - hard to see from ten feet away. Another option is to insert a multi-band vertical (Hustler, Hygain, etc) into a thin-walled PVC pipe. Finances permitting, the small Steppir vertical will suffice for the higher HF frequencies - add a loading coil for the lower frequencies.

BTW, the FCC OTARD regulations allow an outdoor "TV" antenna mounted on the roof inclusive of a mast extending 12 ft above the roof-line.  A little creativity will open up lot's of stealth antenna possibilities.

A VHF/UHF stealth antenna is also easy.  If you can extend a roof vent so that it's 19", you an tape a vertical to the outside.  Lot's of other possibilities.

Scour  to Internet to see what others have done.
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KH6AQ

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Re: Radiant Barrier
« Reply #7 on: April 14, 2020, 12:42:23 PM »

I believe you're right that the aluminum foil radiant barrier could be an issue. Assuming they're 24" x 16' they won't be resonant below 10 meters and may or may not be an issue on lower frequencies. A nearby dipole will induce RF current and they should re-radiate it. If the strips are at right angles to the dipole less current will be induced. Given dimensions I can run an EZNEC model to get a rough idea of what you're up against.

The safe way to go is the 20' flagpole vertical. Sixteen x 20' (shorter will work) radials and an autotuner at the base and you're on the air from 60-6 meters. I don't know of an autotuner that will load a 20' vertical on 80 meters. EZNEC shows a top hat consisting of 8 x 26" spokes can help either autotuner to load it on 80 meters. Spokes made of "piano wire" will work and DX Engineering sells high quality stainless steel spokes for their HotRodz top hat kit.

The MFJ-993BRT has 22 uH but the flagpole needs 26 uH. The Icom AH-4 needs a 23' vertical to load on 80 meters.
« Last Edit: April 14, 2020, 12:46:05 PM by KH6AQ »
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K4NYM

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Re: Radiant Barrier
« Reply #8 on: April 14, 2020, 01:54:42 PM »

mag loop?

I thought about that. The problem is where to put it where it won't be seen.
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K4NYM

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Re: Radiant Barrier
« Reply #9 on: April 14, 2020, 02:01:37 PM »

Put up an antenna and listen.  RF can leak through narrow gaps.  But, a dipole attic may not have much height. 
A vertical normally works better than a low dipole.  Particularly a dipole next to noise generating devices.

I put up a 20 ft flagpole and found it resonant on 30M.  With an automatic tuner at the feedpoint it was usable on 40M through 10 meters. 
I was able to work Japan with 5 watts using the JT65 digital mode using it.  It was harder to work Japan that way than to work them on QRP CW.
With all the folks on FT8 digital it seems easier now to work DX on CW.

Zak W1VT

Zak, when I lived in Maryland I was in a town house. I had a 10-80 meter dipole in a zig-zag pattern in the attic. I had a Drake TR4 and an MFJ tuner. I was able to load up 10-80 with an acceptable SWR. I had my fair share of CW DX to Europe. Of course, I did't have that radiant barrier. I really want to get on a certain net on 80 meters, so finding a way to accomplish that will be a challenge. That flag pole vertical seems like it's staring me right in the face. I'll have get some help installing it if I go that route, but it may be the choice that makes the most sense.
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K4NYM

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Re: Radiant Barrier
« Reply #10 on: April 14, 2020, 02:09:43 PM »

Is it possible to lay insulated dipole wires actually on the roof? My house has a hip roof with some "hidden" dips. It could be possible to mount a balun without being seen and then run insulated wire of the same color as the composite shingles; tucking the wire some shingles along the way. I'm wondering whether the aluminum radiant barrier on the other side of the roof with reflect the signal back. Just a thought.
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K4NYM

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Re: Radiant Barrier
« Reply #11 on: April 14, 2020, 02:10:58 PM »

Just wondering what type of roofing the house has (cement tile, composition, etc.) and are the walls stucco?

The shingles are composite and the walls are concrete block covered with stucco.
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K1VSK

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Re: Radiant Barrier
« Reply #12 on: April 14, 2020, 06:07:23 PM »

Is it possible to lay insulated dipole wires actually on the roof? My house has a hip roof with some "hidden" dips. It could be possible to mount a balun without being seen and then run insulated wire of the same color as the composite shingles; tucking the wire some shingles along the way. I'm wondering whether the aluminum radiant barrier on the other side of the roof with reflect the signal back. Just a thought.

The foil will interact with whatever you lay on top of the shingles. If you can’t/don’t want to install some type stealth antenna in violation of your rules, try the flagpole option as I suggested and hope the HOA doesn’t figure out it’s actually an antenna.

If you have a pool cage, some guys have successfully loaded that up as an antenna with success after experimenting with bonding various sections in combination.
« Last Edit: April 14, 2020, 06:09:46 PM by K1VSK »
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KR6NU

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Re: Radiant Barrier
« Reply #13 on: April 15, 2020, 06:10:21 AM »

Is it possible to lay insulated dipole wires actually on the roof? My house has a hip roof with some "hidden" dips. It could be possible to mount a balun without being seen and then run insulated wire of the same color as the composite shingles; tucking the wire some shingles along the way. I'm wondering whether the aluminum radiant barrier on the other side of the roof with reflect the signal back. Just a thought.

I've seen wire antennas laid on the roof as you suggest work quite well.  The unknown in this case is the effect of the roof underlayment.  It might be worth a try before you go to the considerable expense and trouble of the flagpole antenna.
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AA4PB

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Re: Radiant Barrier
« Reply #14 on: April 15, 2020, 08:31:15 AM »

If you lay a wire antenna on the roof, that aluminum foil radiant barrier will be less than an inch away - not good. I'd opt for the flag pole antenna with some buried radials.
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Bob  AA4PB
Garrisonville, VA
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