I've been thinking about a 70cm antenna made by using copper tape on a
window. It seems that I can get a 50 ohm match by drooping the two
radials about 38 degrees below horizontal. Of course, I don't know how
to include the effects of glass on the antenna nor rectangular coppper,
but it is a starting point. The azimuth pattern looks very good
according to EZNEC.

Any thoughts?
N1JLS

John S wrote:
I've been thinking about a 70cm antenna made by using copper tape on a
window. It seems that I can get a 50 ohm match by drooping the two
radials about 38 degrees below horizontal. Of course, I don't know how
to include the effects of glass on the antenna nor rectangular coppper,
but it is a starting point. The azimuth pattern looks very good
according to EZNEC.

Any thoughts?
N1JLS

Make sure the window is not coated (highly effient dual-pane glass
normally is coated to shield IR radiation). The coating is metallic.

On 16 Nov 2016 16:58:21 GMT, Rob wrote:

John S wrote:
I've been thinking about a 70cm antenna made by using copper tape on a
window. It seems that I can get a 50 ohm match by drooping the two
radials about 38 degrees below horizontal. Of course, I don't know how
to include the effects of glass on the antenna nor rectangular coppper,
but it is a starting point. The azimuth pattern looks very good
according to EZNEC.

Any thoughts?
N1JLS

Make sure the window is not coated (highly effient dual-pane glass
normally is coated to shield IR radiation). The coating is metallic.

Yep. The Low-E coating makes an excellent RF shield and short. Try
it with an HT or cell phone, comparing the signal strength with and
through the glass.
http://buyat.ppg.com/glasstechlib/128_TD-151-Radio%20and%20Microwave%20Frequency%20Attenuation% 20in%20Glass.pdf
Looks like 30-40dB loss at UHF through Low-E glass.

Window glass also has a dielectric constant of about 6.5, which will
shorten the tuned length of the antenna elements by the square root of
the dielectric constant.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 11/16/2016 11:39 AM, Jeff Liebermann wrote:
On 16 Nov 2016 16:58:21 GMT, Rob wrote:

John S wrote:
I've been thinking about a 70cm antenna made by using copper tape on a
window. It seems that I can get a 50 ohm match by drooping the two
radials about 38 degrees below horizontal. Of course, I don't know how
to include the effects of glass on the antenna nor rectangular coppper,
but it is a starting point. The azimuth pattern looks very good
according to EZNEC.

Any thoughts?
N1JLS

Make sure the window is not coated (highly effient dual-pane glass
normally is coated to shield IR radiation). The coating is metallic.

Yep. The Low-E coating makes an excellent RF shield and short. Try
it with an HT or cell phone, comparing the signal strength with and
through the glass.
http://buyat.ppg.com/glasstechlib/128_TD-151-Radio%20and%20Microwave%20Frequency%20Attenuation% 20in%20Glass.pdf
Looks like 30-40dB loss at UHF through Low-E glass.

Window glass also has a dielectric constant of about 6.5, which will
shorten the tuned length of the antenna elements by the square root of
the dielectric constant.


Excellent point, guys. I forgot all about that. Thanks.

I've been thinking about a 70cm antenna made by using copper tape on a
window. It seems that I can get a 50 ohm match by drooping the two
radials about 38 degrees below horizontal. Of course, I don't know how
to include the effects of glass on the antenna nor rectangular coppper,
but it is a starting point. The azimuth pattern looks very good
according to EZNEC.

Any thoughts?

Yes, it's been done successfully... it's a basic ground-plane antenna.

There will be some amount of loading from the glass, which will
probably require you to shorten the elements slightly to achieve
resonance where you want it. The use of wide conductors will have a
similar effect - EZNEC may be able to model this. If you have an
antenna analyzer you could just cut-and-try by making a prototype with
the copper strips attached to a piece of cardboard, trim until you get
a match you like, and then cut a second set of copper strips and
attach to the glass.

You may want to add a ferrite bead-balun to the coax just below the
feedpoint. Not strictly necessary but it can help keep RF off of the
outside of the coax (from which it would radiate on the indoor side,
probably squinting some power in useless directions).

One caution, though: before you start this, consider whether your
window uses a "low-E" energy-saving glass. This sort of glass has a
thin film of vacuum-deposited metal on one side, and it's likely to be
conductive and lossy enough to make your antenna not work at all well.

On 11/16/2016 12:49 PM, Dave Platt wrote:
I've been thinking about a 70cm antenna made by using copper tape on a
window. It seems that I can get a 50 ohm match by drooping the two
radials about 38 degrees below horizontal. Of course, I don't know how
to include the effects of glass on the antenna nor rectangular coppper,
but it is a starting point. The azimuth pattern looks very good
according to EZNEC.

Any thoughts?

Yes, it's been done successfully... it's a basic ground-plane antenna.

There will be some amount of loading from the glass, which will
probably require you to shorten the elements slightly to achieve
resonance where you want it. The use of wide conductors will have a
similar effect - EZNEC may be able to model this. If you have an
antenna analyzer you could just cut-and-try by making a prototype with
the copper strips attached to a piece of cardboard, trim until you get
a match you like, and then cut a second set of copper strips and
attach to the glass.

You may want to add a ferrite bead-balun to the coax just below the
feedpoint. Not strictly necessary but it can help keep RF off of the
outside of the coax (from which it would radiate on the indoor side,
probably squinting some power in useless directions).

One caution, though: before you start this, consider whether your
window uses a "low-E" energy-saving glass. This sort of glass has a
thin film of vacuum-deposited metal on one side, and it's likely to be
conductive and lossy enough to make your antenna not work at all well.



Good info. Thanks.