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The Radiant Barrier Myth

Frank Graves (K5OX) on September 14, 2017
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One of the most common myths today is related to radiant barrier roofing. In hotter climates this type of roofing is common, and as the owner of a house with such roofing, I almost gave up ham radio.

For me it was a real downer, as I had purchased this house new 15 years ago, when the original buyer's loan fell through. I was excited by the high pitched roof and the resulting spacious attic. I didn't know about radiant barrier roofing at the time. It was a rather new product and an expensive upgrade.

When I moved in, and took a real tour of the attic I noticed that the inside of the roof was covered in what appeared to be aluminum foil. I can't describe the sinking feeling and I knew no antenna could transmit through metal.

I was wrong. First of all, it was not a contiguous "shield." I looked the product up and at least one inch of foil is omitted on the edge of the board. This leaves a two-inch gap between the boards. Just to make sure I put a 20-metermobile whip and laid a single wire counterpoise on the attic floor. This antenna performed outstanding. From near Houston, I was having many 5,000 to 8,000 mile contacts with 100 watts. The question remained why? I didn't know. And it took a lot of reading and asking questions to get a grip on just what the mystery was.

First of all, radiant barrier as used in home construction is a lousy shield. Similar materials are use to make "silent" rooms but with a major difference. A much more expensive type of barrier is used and in these secure rooms every wall, ceiling, floor, and fixture must be covered. Even so, the target is to block signals above 100 MHz.

So, shielding a room is expensive and requires a great deal of expertise and there are companies that specialize in this type of installation. My radiant barrier roofing is TYVEC and is a type of 8x10 foot roofing board the is made for hot humid areas. It is designed to reflect heat from the sun and also to allow humidity to escape out of the attic. It appears to do just that, and my air conditioning bills are a fraction of what they used to be.

In order to understand why my 20-meter antenna works we need to understand a little about antennas and waves. My helically wound mobile whip is only 7 feet long and the counterpoise is a 1/4 wave or roughly 16.5 feet.

The size of the antenna has nothing to do with the size of the wave excited by the antenna. At 20 meters a wavelength is fixed. It is equal to 20 meters or approximately 65 feet. The longest part of my attic is about 55 feet. The wave is bigger than my attic! Put simply, the wave is so large that it forms outside the house. Then you have to look at the far field where the wave produced by an antenna is "assembled" be it horizontal or vertical. High YAGI antennas work well when they are high because of ground gain and the far field production of low angle radiation.

Keep in mind also that no house is likely to be 100 shielded at HF frequencies. I have had success with my attic G5RV JR on 6 meters. Although I think there is some attenuation, I have no problem making 1300-mile contacts during Es openings. At UHF the wavelength is small and the roof will cause significant attenuation. 2 meters is in a gray area that I haven't personally tested. But my cell phone works just fine in the attic; reflected energy, no doubt.

So let's dispel the myth once and for all. I live in a heavily deed restricted no antenna neighborhood. And I unknowingly purchased a house with heat/ humidity barrier roofing. I work lots of DX and use CW mostly. I do not use digital modes. I have used my antennas outside temporarily and don't notice any improvement.

Think about it. Many hams use ground mounted vertical -- radial systems in urban areas. Do the neighbor's houses really cause significant attenuation? It's very doubtful.

In closing, keep in mind that we don't always have an easy choice in our selection of places to live. After I married, my wife and I lived in a third story wood frame apartment. This is a long time ago, but I put my HW100 in a walk in closet and used a 8 foot wooden dowel wrapped in aluminum foil and base loaded and tapped it for matching. I worked DXCC, WAS and WAC with this arrangement. Also I used a single counterpoise.

Contrary to QST's recent editorial we didn't sign the contract by choice. We typically for financial, commute considerations and school districts haven chosen our home based on needs other than ham radio. The Houston metro area is not a "big gun" area. This area for whatever reason does not have zoning and deed restrictions are inescapable. And today so are radiant barrier building materials in most new homes.

Keep your perspective. Ham radio is a hobby, and challenges can be a lot of fun. I hope that the Senate passes the parity bill, but if they don' it's not the end of the world. When I found out I had a "tin" roof, I thought so, but it was preconceived myths that persist in this great hobby. Again, let me state it one final time. Heat barrier roofing offers little to no attenuation at HF frequencies in typical installations. Always try and test things yourself. Forget the naysayers. Dispels the myths!

Member Comments:
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The Radiant Barrier Myth Reply
by AD0AR on September 14, 2017 Mail this to a friend!
Metal roofing: Disappointment. I had a friend who had a original metal vertical standing seam roof on his house 100+ years old. He had a unused brick chimney, so he shoved a section of tower down the chimney and mounted a HF vertical on it. He was getting out all over the place with this pure simplicity setup- and antenna over a "perfect ground" until the house was re-roofed with asphalt due to a hailstorm that punched a few leaks through the tired copper roofing. All the magic left the setup and it no longer performed well.
20 years later I had a vertical standing seam screw together roof installed on my house. Screwed right through the roofing was a tripod and I mounted a hf vertical.
All I got was massive RFI and an antenna that refused to tune properly. - The big difference? His was a copper standing seam roof soldered together and mine was screwed together... Even isolating the antenna from the roof made no difference. The only thing that worked was using a fiberglass mounting pole electrically insulating/isolating the antenna ground from the roof AND using a elevated counterpoise. Now it works wonders but was much larger than expected so don't expect wonders over a metal roof, unless it is a single continuous piece of metal, like a car body.
 
RE: The Radiant Barrier Myth Reply
by KF4HR on September 15, 2017 Mail this to a friend!
Where there is a will, there is a way. Antennas work best when they're kept high and in the clear, but when forced with a compromised antenna situation, the CW mode is a good choice.
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 15, 2017 Mail this to a friend!
My comments were related to a roofing material that is roofing board that has a metal foil laminate, usually on the side facing the attic. True, detuning of the antenna can occur. A G5RV JR 20 feet high is not a great antenna, but I get excellent results, on par with what I would expect outside.

Maybe someone else can explain why things work as well as they do, better than I can. The reasons are complex and have to do with wave excitation, near field and far field antenna theory.



 
The Radiant Barrier Myth Reply
by KC8FRJ on September 17, 2017 Mail this to a friend!
A better title might be a Housing Radiant Barrier problems are frequency dependent. It certainly plays havoc with any VHF and UHF antenna I place in my attic. Yet 50MHz dipoles seem to work splendidly.
 
RE: The Radiant Barrier Myth Reply
by K6AER on September 17, 2017 Mail this to a friend!
The near field capacitance of any piece of metal (Large or Small) will affect the frequency, VSWR and radiation patters of any antenna. Depending on frequency and distance it can radically change the radiation pattern, as well as gain. Any antenna does better mounted as high as possible and in the clear. Those panels may be reflective at VHF and only disruptive at HF.

Attic antennas are at best a compromise if the antenna cannot be mounted outside. Also, do the reflective nature of large conductive metal sheets, it may reflect interference sources found inside the home increasing the HF noise level.
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 17, 2017 Mail this to a friend!
A 4x8 foot metal foil panel placed two feet from a 40 meter antenna will have very little effect on antenna gain, radiation pattern or SWR. There is no theory to support this conception.

You would have to have a nearby object be resonant at the frequency in use to have a parasitic coupling exist.

Certainly high and in the clear is optimum. An attic is a very poor choice in a single story house like mine, simply because it is very difficult to get an effective height. But if you cannot put an antenna outside because of HOA covenants, the attic may be the only solution. And if you operate HF primarily, there is no reason that some sort of indoor or attic antenna won't work. It's low height if horizontal will make DX harder because of a high angle of radiation, but DX can be worked. CW and Digital will yield better results with low dipoles, especially ones less than full size.

When I talk of near field losses, this includes actual antenna radiation resistance losses (e.g. loading coils). Far field is an effect that increase gain with an increase in horizontal antenna height. In general, the higher the horizontal antenna, the more gain due to ground reflections.
 
RE: The Radiant Barrier Myth Reply
by KB4QAA on September 17, 2017 Mail this to a friend!
<<A 4x8 foot metal foil panel placed two feet from a 40 meter antenna will have very little effect on antenna gain, radiation pattern or SWR. There is no theory to support this conception.>>

My EZNEC+ simulation shows no change in Elevation pattern, however it degrades the Azimuth pattern by 5dB, and worsens SWR from 10:1 to 13:1.

This with a 4x8 panel with top edge at 17ft angle at 45degr downward to 13ft, the 40m dipole cut for 7.1Mhz at 15ft.

Sorry, you can't place metal objects near antennas without having effect. They do NOT need to be resonant at a given frequency in order to couple and have undesired effects.
 
RE: The Radiant Barrier Myth Reply
by KB4QAA on September 17, 2017 Mail this to a friend!
Final point: If nearby objects had no effect on antennas then we would just attach them to the walls of building, metal sheds or just lay them on the soil. There would be no need to elevate them!
 
The Radiant Barrier Myth Reply
by K4FMH on September 17, 2017 Mail this to a friend!
Frank,

Let me echo your comments and also confirm them in my own very similar situation. Five years ago, we built a custom house and during a walk-through of the attic after roofing, I came to a dead stop when I saw the foil-backed radiator barrier! I went down to my truck to get my HT. I hit all of the repeaters in my attic (some 25' above ground) that I did on the street by my truck. I breathed somewhat of a relief. I had a dual band Ventenna installed by my plumber. It's about 40' above ground. Works terrific but is outside the foil-backed radiator barrier.

I had the electrical crew install a #14 stranded insulated wire for a "somewhat" horizontal loop tucked just under the edge of the shingles. The wire came into my attic and was connected to a balun (loop custom built by Bruce NU0R) and on to my Ameritron remote switch. I've since installed an MFJ 80/40M dipole in that attic. One of my original contacts on HF using the loop was Steve Katz WB2WIK on our respective Drake TR-7s. His 5-9 report said I was the only signal on the 20M frequency. I've worked a number of other stations with no real issues. I will do some additional work once the heat subsides to a comfortable level to attack some RFI noise from tankless water heaters and HVAC units in the attic.

My experience is very much like yours: the foil backed radiator barrier works for heat, not RF insofar as I can notice. The lack of bonding between the plywood sub-roofing undoubtedly helps. We love the lower utility bills that this barrier plus the ridge cap provides.

Thanks for posting this article. I had let Gordon West know this on a Skype program he did for our club and Gordo was shocked at my results. Your article will help ensure that hams test rather than assume.

73,

Frank
K4FMH
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 17, 2017 Mail this to a friend!
I don't have EZNEC here, and it has been a while since I've used it. But I may try to get it and repeat your results. How did you establish a connection point for an insulated panel? The roofing board is essentially insulated from anything else and it would have capacitance to ground but otherwise a free space object. How do model this in EZNEC?

Did you mean 1:1 to 13.1 or 10:1 to 13:1 as typed?

I appreciate your taking the time to model the scenario.
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 17, 2017 Mail this to a friend!
This Comment about metal sheds and laying antennas on the ground is not related to the topic being discussed. The first thing to ensure in an attic installation is that you follow well known safety and antenna installation guidelines. I would never recommend putting the antenna closer than necessary to metal to avoid arcing and capacitive proximity effects. In my case I chose a 2 foot distance. Not for any theoretical reason but just ham radio common sense. I also used end insulators - because why not?

I used an RF 1:1 Current Choke between the balanced feed of the G5RV JR and the 35 ft of LMR-400 coax to my antenna tuner. I could have used no Choke and cheap RG58. But I knew enough to know that the Choke will reduce RF in the shack and the LMR-400 would have little SWR related loss.

If you want to get silly. Model a metal shed with a wire attached. Chances are it will radiate. I have taped wire ends of dipoles to walls before temporarily, and they resonated as expected. Finally, antennas laying on the ground (insulated) have been used successfully. I forget just where I read that and I would have to search my 30+ book antenna library including ARRL, RSGB and other respected sources.
 
RE: The Radiant Barrier Myth Reply
by KB4QAA on September 17, 2017 Mail this to a friend!
I molded the panel as an independent object, not connected to the antenna in any way.

My panel had four sides, a center parallel horizontal conductor and two vertical cross conductors. Long side (8ft) is horizontal. One could use many configurations.

My model produced a 10:1 SWR at 3.6Mhz, but the exact number is unimportant due the multitude of variables.

Capacitive coupling does not require any connections, whether to ground, building, isolated panels or wires.
 
RE: The Radiant Barrier Myth Reply
by KB4QAA on September 17, 2017 Mail this to a friend!
Correction 10:1 at 7.1Mhz!
 
The Radiant Barrier Myth Reply
by KQ6XA on September 18, 2017 Mail this to a friend!
Especially for HF and 6 meters, all these types of metal structures can be easily used as antennas by running insulated wire dipole antennas as close as possible to them.

A good ferrite balun fed with coaxial cable with a coaxial ferrite choke inline is needed to keep receive noise and RFI to a minimum.

Either use a variable tuned antenna, prune the antenna, or use an antenna tuner.

With the proper coupling, those metal structures will radiate.
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 18, 2017 Mail this to a friend!
I don't necessarily disagree with the nature of capacitive coupling. But it can get very confusing determining the exact effects of proximity issues. For instance, the wire 2 feet from a free space 4x8 foot piece of aluminum foil would seem to have an insignificant amount of capacitance. because the surface area of the wire is very small and 2 feet away from the much larger piece of foil.

I'm not sure, to be honest, how to analyze this scenario as a radiating antenna's voltage and current phase ratio varies from the center to the ends of a dipole. I believe proximity effects are higher at the ends as the voltage is higher. Also the antenna and the foil plate would have a common capacitive connection due to their mutual but unequal capacitance to ground. But this capacitance from
a circuit analysis would very small.

Also it would seem complex to compare a radiating electromagnetic wave that is about 136 feet, to the effects of a small amount of capacitance. These to me are questions based on the way actual antennas behave. My G5RV JR for instance behaves as expected in the my attic surrounded by isolated foil backed panels almost the same as it does outside 20 feet high. What I don't understand is that in my 58 years of ham radio I have ran many 40 meter dipoles near metal rain gutters, electrical wires and God knows what else and I have never experienced extremely high SWRs even remotely close to 10:1.

My question is why doesn't the model reflect reality?
 
RE: The Radiant Barrier Myth Reply
by KF7ZFC on September 18, 2017 Mail this to a friend!
How would a Mag loop like MFJ 1788 operate in this situation? This is the choice I have either outside only 5 feet from the house (stucco with chicken wire) or the attic with the foil panels?

 
RE: The Radiant Barrier Myth Reply
by K5OX on September 19, 2017 Mail this to a friend!
A mag loop is a very high Q antenna and nearby objects can detune it. This is quite a bit different than a dipole that is relatively broadbanded and not nearly as sensitive to nearby objects. Attenuation of the radiated signal should not be significantly different, as the operating frequency determines the size of the radiated wave, not the size of the antenna.

Although I have not lived in a "stucco" house, I have read that they can be problematic. An inside dipole, even loaded, may give better results as the more of the signal may be directed to the roof which may have less attenuation. The 1/2 wave loop I used on 6 meters was not a high Q magnetic, but a dipole folded into a square and was very broadbanded and horizontal and only 11 feet high. But at 6 meters the major lobe at this height is about 30 degrees a good compromise for Es use.

Although my favorite mode is CW, the digital modes have 10 - 25 DB abvantage over CW and even more over SSB. So digital may at least get you some DX.


 
The Radiant Barrier Myth Reply
by AD7II on September 21, 2017 Mail this to a friend!
Are you sure that the whip is the antenna and the wire is the counterpoise? Or could it be the other way around?
 
RE: The Radiant Barrier Myth Reply
by KB4QAA on September 21, 2017 Mail this to a friend!
These are not Marconi (vertical) antennas, nor nested. They are Inverted L's arranged back to back.

The ladder line does not perform any phasing function because it is shorted at the bottom.
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 21, 2017 Mail this to a friend!
In the case of of a vertical with a single counterpoise according to Moxon, it is best described as a dipole. I have the mobile whip setup inside on the first floor in a room with cathedral ceilings and the horizontal 1/4 horizontal "counterpoise" is 3 feet high. And the 7 foot 20 meter whip is vertical.

I just tested it with reverse beacons and it is picked up after two CQs by beacons 1,500 miles away and none closer. Whereas my G5RV JR is also picked up quickly (on 20M) by many reverse beacons, but most are about 600 miles away.

Testing an antenna with the reverse beacon network doesn't lie. For whatever reason the vertical with counterpoise shows a much lower angle of radiation than the G5RV JR. But the G5RV JR is getting out very nicely for a "shielded 13:1 SWR" antenna. My whole point in this article is you just don't know if something will work unless you try it. For what it's worth my MFJ Versatuner tunes the G5RV JR to 1:1 across from 14 to 14.050 without retuning.

I have a screen capture of the reverse beacons for the G5RV JR from DXMAPS. Tests with the reverse beacons were made today at 2300 UTC. You judge an antenna on performance, not models. Models are a guide, but not designed for to emulate nearby objects such as power wiring very well.
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 22, 2017 Mail this to a friend!
Iím not quite sure what you mean by ďtheseĒ antennas? G5RVs? If so I disagree that they are two INV Ls back to
back. The ladder line is indeed feeding a balance antenna, even if not resonant. The ladder line is only shorted at the bottom in one specific case. This is when a full size G5RV is worked against ground on 160 meters. In this (single) case you might draw a parallel to a T top loaded antenna. A radial or ground screen connection and matching network would have to exist.

A G5RV as designed by Varney was optimize for best performance on 20 meters using 51 per leg. The ladder line was indeed a matching transformer and transforms to approx 50 ohms on some bands. Itís disadvantage is that the SWR is quite high on other bands.

SWR deficits are relative to transmission line losses.There is little loss in ladder line, but the coax should be kept as short as possible and low loss 213u or LMR 40 should be used.

A G5RV JR as I have is not a true G5RV. It is simply scaled in half and itís only andvantage is that it offers a flattop of 51feet total for 40 meters and provides a coax tunable match to an antenna tuner on most bands making it a convenient multi-band antenna.

Because it requires an antenna tuner and is NOT critical to resonance it makes it a fair choice for attic antenna. I thought stated clearly that for a low dipole itís operationhas been normal in my 48 years experience as a ham. If you want to keep describing inaccurate reasons why it wonít work. Your effort is futile, because it works well. It may not in other installations. But the message here is to dispel naysayers. Try something if it might work. Practice and theory are not easily reconcilable.
 
RE: The Radiant Barrier Myth Reply
by W9IQ on September 22, 2017 Mail this to a friend!
Frank,

We should simply agree that it comes down to a question of antenna system efficiency and directivity. You have shown that the antenna gets out to some unknown degree and you are happy with the results despite some potentially formidable barriers.

You will likely not be able to quantify either the efficiency or directivity so there is little point debating either one.

- Glenn W9IQ
 
RE: The Radiant Barrier Myth Reply
by K5OX on September 23, 2017 Mail this to a friend!
Glen,

Very well put. For me the attic system works better than I expected, but calculating its efficiency as you stated, is impractical as so many variables exist.

If you are satisfied with your antennaís performance thatís what matters. I do notice with my antenna that it seems to under perform for DX. This I attribute to its low height. This is why I am putting a vertical/counterpoise hidden by trees in the back yard.

I expect it to have better DX performance. But how much better, I will have to try it to see if it offers the performance I hope for. There is no way, without trying, that I will know if the new antennas performance will satisfy me.

I think that your antenna choices should be based on sound theoretical principals, but how well an antenna works, depends on whether you find it satisfactory. And as you stated, this is relative, unquantifiable thing.



 
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