How to make a simple outdoor antenna for a Weather Radio

[olds...@tubes.com]

I have a weather radio with a telescoping antenna. But it also has a
jack for an external antenna. The jack is a RCA jack, which is not real
common for an antenna connector, but it will work.

I live in an all metal covered home, so I dont get good reception
indoors. My goal is to make something real simple, from stuff I have
laying around, that I can connect to the rain gutter outside and run
some coax inside the house.

I have lots of tv coax, and a RCA plug. I have some plastic material
which should work for the attachment center piece. I'm thinking of just
attaching two bars, one on each side, using something like coat hanger
wire, or even some heavy #8 solid copper wire.

These radios operate at 162.400, 162.425, 162.450, 162.475, 162.500,
162.525, and 162.550 MHz.

How long should these wires be? Or should I make it like a bow tie
shaped antenna? I might even have a broken tv antenna in my junk pile
that I can salvage some of the cross bars and even the insulators. (got
to look in my scrap metal pipe and see if it's still there).
But once again, I need to know the length.

OR - Maybe there is something even more simple that I can rig up.

Suggestions????

[tabb...@gmail.com]

I'd search for VHF antenna.

[sdy]

Try an old tv antenna, a pair of rabbit ears.

[artie]

In article <udcfdcdtsqp5s339k...@4ax.com>,

You should try a simple ground plane antenna, which is a vertical
element surrounded by four radial elements pointing down at an angle.
Google for ground plane antenna design -- you can make one from a chunk
of RG-6 satellite cable, with the vertical element 18 inches (18 and
1/8 is a little better) and the radials also the same length.

[rickman]

The FM band is 88 to 108 MHz roughly. So your frequency is about in the
same band, slightly higher, just a bit below channel 7 in the US. So a
VHF TV antenna should do the job nicely. VHF would be the big one, not
the one with the little elements which would be UHF. The one with
elements that are about a yard long.

You can use all the same methods of bringing the signal into the house.
Do you know the impedance of your RCA jack input? The manual would have
to provide that info. If it is 50 or 75 ohms you can use the coax
directly pretty effectively. If it is 300 ohms you might want to use a
balun transformer. Normally a 300 ohm input on a receiver will have a
pair of screw terminals, but I have no idea what type of input would be
expected to use an RCA jack.

If you just want to make a simple dipole, you just need a pair of
elements each 3 feet long. To connect them to twin lead, just connect
them. To connect to coax use a balun transformer. I don't know that
the 8 gauge wire will support itself or certainly won't in a wind.
There is also a type of loop antenna you can make from 300 ohm twin
lead. It only needs to be 1/2 wavelength (3 feet) end to end. It's
like the dipole, but the ends of the twin lead are connected making it a
loop even though the loop is not opened up. Here is a link for some
details.

http://hf-antenna.com/003/

This will get you something to work with. If you want more, you can use
a preamp mounted by the antenna. Seems the weather radio signal is
vertically polarized, so the element will work best aligned vertically.

A vertical antenna might work ok for this. I don't know much about
making them. Here are a couple of links.

http://www.qsl.net/wrav/2mground.htm

http://www.weather.gov/cae/antenna.html

http://www.jpole-antenna.com/2013/02/24/increase-the-range-of-your-noaa-weather-radio/

Or you can just buy one.

https://www.walmart.com/ip/Midland-Through-Window-Mount-Weather-Band-Antenna-With-Installation-Material/10966174?wmlspartner=wlpa&selectedSellerId=1122&adid=22222222227000037920&wl0=&wl1=g&wl2=c&wl3=40839389672&wl4=pla-78652587992&wl5=9059750&wl6=&wl7=&wl8=&wl9=pla&wl10=101593696&wl11=online&wl12=10966174&wl13=&veh=sem

Why didn't you google this? There are tons of hits.

A better newsgroup might be rec.radio.amateur.antenna

--

Rick C

[dca...@krl.org]

On Sunday, March 26, 2017 at 12:25:40 PM UTC-4, rickman wrote:

>
> The FM band is 88 to 108 MHz roughly. So your frequency is about in the
> same band, slightly higher, just a bit below channel 7 in the US. So a
> VHF TV antenna should do the job nicely. VHF would be the big one, not
> the one with the little elements which would be UHF. The one with
> elements that are about a yard long.
>

>

> Rick C

I looked around on the internet and did not find what orientation the antenna should be. But I think the signal is polarized vertically. So a vhf tv antenna would work well, but it might need to have the elements pointing up and down instead of horizontal.

Dan

[tom]

<dca...@krl.org> wrote in message
news:55c60866-f548-424c...@googlegroups.com...

+++++++++++++++++++++++++++

The NWS VHF signals are vertical polarized.

[rickman]

It was on the Government web site, vertical. Makes sense. You don't
want to need an antenna rotator to receive weather signals.

--

Rick C

[John S]

Receiving is not as demanding as transmitting (usually). Strip your coax
outer jacket and shield about 18 inches from the far end. Put it outside
and elevate it. It should be vertically oriented.

If it gives you what you need, then consider weather-proofing it. Like
using a PVC pipe or some goo around the exposed surfaces.

[Jasen Betts]

On 2017-03-26, olds...@tubes.com <olds...@tubes.com> wrote:
> I have a weather radio with a telescoping antenna. But it also has a
> jack for an external antenna. The jack is a RCA jack, which is not real
> common for an antenna connector, but it will work.
>
> I live in an all metal covered home, so I dont get good reception
> indoors. My goal is to make something real simple, from stuff I have
> laying around, that I can connect to the rain gutter outside and run
> some coax inside the house.
>
> I have lots of tv coax, and a RCA plug. I have some plastic material
> which should work for the attachment center piece.

I've seen RCA plugs used for 75 ohm VHF antenna connections in
consumer eqipment before. they're fairly common inside, but less
common externally.

> I'm thinking of just
> attaching two bars, one on each side, using something like coat hanger
> wire, or even some heavy #8 solid copper wire.
> These radios operate at 162.400, 162.425, 162.450, 162.475, 162.500,
> 162.525, and 162.550 MHz.
>
> How long should these wires be? Or should I make it like a bow tie
> shaped antenna? I might even have a broken tv antenna in my junk pile
> that I can salvage some of the cross bars and even the insulators. (got
> to look in my scrap metal pipe and see if it's still there).
> But once again, I need to know the length.
>
> OR - Maybe there is something even more simple that I can rig up.
>
> Suggestions????

vertical folded dipole.

image: https://www.comsystems.com/VHF%20antennas/vhf-base-antenna-ad39-2

perhaps made from one of the loops, and the balun, from an old
VHF antenna, you want about 630mm over the large dimension, but
anywhere in the ballpark will probably work well-enough.

size computer: http://www.changpuak.ch/electronics/Dipole_folded.php


--
This email has not been checked by half-arsed antivirus software

[Jeff Liebermann]

On Sun, 26 Mar 2017 07:37:26 -0500, olds...@tubes.com wrote:

>I have a weather radio with a telescoping antenna.

Maker and model please?

>But it also has a
>jack for an external antenna. The jack is a RCA jack, which is not real
>common for an antenna connector, but it will work.

Weather station transmitters produce rather strong signals and do not
require a sensitive receiver. Some inefficiencies and losses in the
antenna system can be tolerated.

>I live in an all metal covered home, so I dont get good reception
>indoors. My goal is to make something real simple, from stuff I have
>laying around, that I can connect to the rain gutter outside and run
>some coax inside the house.

That's a common problem. Look into proper cable entries first. For
example:
<http://www.ebay.com/itm/Winegard-CE-2000-RV-TV-Antenna-Roof-Cable-Plate-With-Screws-/231375922138>

>I have lots of tv coax, and a RCA plug.

RG-6u will work. RG-59 is garbage. Make sure the cable is rated for
outdoor use (i.e. non-penetrating jacket and UV resistant). The
mismatch loss between 50 ohms and 75 ohms is tiny for this application
and can be ignored.

>I have some plastic material
>which should work for the attachment center piece. I'm thinking of just
>attaching two bars, one on each side, using something like coat hanger
>wire, or even some heavy #8 solid copper wire.

Find an SO-239 connector and build a simple ground plane. Lots of
ways to do it:
<https://www.google.com/search?q=so-239+ground+plane+antenna&tbm=isch>
The center driven element is 1/4 wavelength long at the weather band
(about 46.1 cm or 18.1 inches). The 4 ground radials are 1/4
wavelength plus about 5%. At the low gain of the ground plane, the
dimensions are not critical.

>These radios operate at 162.400, 162.425, 162.450, 162.475, 162.500,
>162.525, and 162.550 MHz.
>
>How long should these wires be?

See above.

>Or should I make it like a bow tie shaped antenna?

No. Bow tie antennas are for where you need lots of bandwidth, such
as covering the TV bands from 54 to 700 MHz with one antenna. The
weather band is tiny by comparison and can use narrow band antenna
designs.

>I might even have a broken tv antenna in my junk pile
>that I can salvage some of the cross bars and even the insulators. (got
>to look in my scrap metal pipe and see if it's still there).
>But once again, I need to know the length.

Length depends on the type of antenna. I suggested a ground plane,
but there are plenty of others that can be calculated. Find something
SIMPLE that you can build, and I can grind the numbers for you. My
disorganized site:
<http://www.LearnByDestroying.com/jeffl/antennas/>

>OR - Maybe there is something even more simple that I can rig up.

How are your carpentry skills? Build a slot antenna. Cut a 1/2 wave
horizontal slot in the side of your building. Connect coax and a
balun at the midpoint. Instant dipole and they don't get any simpler:
<https://www.google.com/search?q=slot+antenna&tbm=isch>
<http://www.antenna-theory.com/antennas/aperture/slot.php>
One catch is that it will be directional so cut the slot on the
correct side of the building.

>Suggestions????

Like I mentioned, cable entry will be your biggest problem. It
doesn't get much simpler than a ground plane antenna. However, if you
experience a weak signal because of your location, a more complicated,
larger, taller, and higher gain antenna might be required.


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

[Tauno Voipio]

On 27.3.17 18:45, Jeff Liebermann wrote:
>
> Find an SO-239 connector and build a simple ground plane. Lots of
> ways to do it:
> <https://www.google.com/search?q=so-239+ground+plane+antenna&tbm=isch>
> The center driven element is 1/4 wavelength long at the weather band
> (about 46.1 cm or 18.1 inches). The 4 ground radials are 1/4
> wavelength plus about 5%. At the low gain of the ground plane, the
> dimensions are not critical.
>

The RF banana plug (SO-239 and plug) is a challenge to get watertight.
The problem is to prevent water from getting between the outer
jacket and the braid.

--

-TV

[Jeff Liebermann]

Yep. A similar ground plane antenna on my roof has an inverted
plastic funnel covering the connector assembly, which is also wrapped
in PTFE water pipe tape under a layer of Scotch 33 electrical tape.
It's been up there for about 15 years without any obvious water
related problems. There was a problem with water puddling on the
SO-239, which I solved with a little RTV silicone seal.

[olds...@tubes.com]

This is the kind of advice I am looking for. I am not looking to spend
money on this. I get a a good signal from the weather service outdoors,
just not inside the metal building. To be sure what you are saying, I
think you are saying to strip back 18" of the coax. Then I should attach
this to something, so the center wire points toward the sky, and the
shield part (also 18") points toward the ground. CORRECT?

I am already thinking I can take a 1/2" cpvc tee and two 18" pieces of
cpvc pipe, and shove this coax inside of it to protect it from the
weather. I can seal the ends of the pipe with silicone caulk. (or pipe
caps). I could easily attach this to my rain gutter with a C-clamp.

[Jeff Liebermann]

On Thu, 30 Mar 2017 16:58:57 -0500, olds...@tubes.com wrote:

>This is the kind of advice I am looking for. I am not looking to spend
>money on this. I get a a good signal from the weather service outdoors,
>just not inside the metal building. To be sure what you are saying, I
>think you are saying to strip back 18" of the coax. Then I should attach
>this to something, so the center wire points toward the sky, and the
>shield part (also 18") points toward the ground. CORRECT?
>
>I am already thinking I can take a 1/2" cpvc tee and two 18" pieces of
>cpvc pipe, and shove this coax inside of it to protect it from the
>weather. I can seal the ends of the pipe with silicone caulk. (or pipe
>caps). I could easily attach this to my rain gutter with a C-clamp.

It's called a coaxial antenna and works quite nicely. Please note
that this is a 70 ohm antenna, not 50 ohms, which shouldn't make any
difference for what you're doing. However, I think you run into a few
problems:

1. You said you had some "cable TV coax" which I'll assume means
RG-6/u. The solid center wire is good enough, but the outer shield is
aluminum foil held together with a small amount of copper braid. When
folding over the outer jacket, the foil is going to break and there's
not enough copper braid to make a suitable ground element. Instead of
RG-6/u, I suggest thicker and heavier RG-8/u.

2. There should be a small gap between the folded over braid and the
outer jacked of the coax cable. My rule of thumb is that the sleeve
should be 2x to 3x the diameter of the coax cable.

3. Shoving the antenna in what is called a "radome" is commonly done
for weather proofing. If you look at similar commercial antennas, you
might notice that they use a fiberglass radome instead of PVC. That's
because PVC is both lossy and will detune the antenna, lowering its
frequency. The degree to which PVC moves the resonant frequency of
the antenna varies with PVC dimensions, thickness, and construction.
Last time I did that, I had about a 10MHz drop at 146MHz or about 7%.
You can compensate by cutting your driven element 7% shorter and/or
check the resonant frequency with an antenna analyzer (MFJ-259). If
you want to check if your material is lossy, just put it in the
microwave oven for a few seconds and see if it gets warm. If it stays
stone cold, it's suitable for a radome. If it gets warm, it will eat
some RF.

4. If weather proofing is a must, such antennas are often filled with
some kind of expanding foam. I tried it with urethane foam and
urethane insulation foam.
<https://www.amazon.com/Liquid-Urethane-Foam-Density-Quart/dp/B007V231P6>
Both worked, but again lowered the resonant frequency of the antenna.
Worse, the amount was totally dependent on the density of the foam. I
could make urethane sorta work, but it wasn't worth the exercise
because there was no easy way to rework the results. Might as well
not fill the radome and add some drain holes in the bottom.

5. You probably don't need a decoupling sleeve to keep the feed line
coax from becoming part of the antenna, but it wouldn't hurt.
<http://4.bp.blogspot.com/-6yN9hSYx2n4/UggVwPp7hlI/AAAAAAAAAgA/RAIlUyX8PAo/s1600/Coax+Dipole+Diagram.jpg>
<http://kr7w.blogspot.com/2013/08/coaxial-dipole-for-portable-backpack.html>

Personally, I think it's easier and better to just build an SO-239
ground plane antenna and forget about the radome.

[mpm]

On Sunday, March 26, 2017 at 8:38:09 AM UTC-4, olds...@tubes.com wrote:

> I have a weather radio with a telescoping antenna. Suggestions????

Just getting the antenna outdoors should help a lot, just keep the coax runs short if using something lossy. Shouldn't really be a problem at VHF, though.

Someone mentioned old TV rabbit ears. I agree.
Let me add: Some models have built-in amplifiers. Try that for sure!

Do you know how distant the transmitter is?
You could have terrain obstructions?
Also, many consumer-grade weather-alert type radios are cheaply made and mass-produced. You might find a commercial-grade model that has much better receiver sensitivity -- but I gather from your post that no funds are presently allocated to the effort. Best of luck!

[olds...@tubes.com]

On Thu, 30 Mar 2017 16:19:12 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>It's called a coaxial antenna and works quite nicely. Please note
>that this is a 70 ohm antenna, not 50 ohms, which shouldn't make any
>difference for what you're doing. However, I think you run into a few
>problems:
>
>1. You said you had some "cable TV coax" which I'll assume means
>RG-6/u. The solid center wire is good enough, but the outer shield is
>aluminum foil held together with a small amount of copper braid. When
>folding over the outer jacket, the foil is going to break and there's
>not enough copper braid to make a suitable ground element. Instead of
>RG-6/u, I suggest thicker and heavier RG-8/u.
>
>2. There should be a small gap between the folded over braid and the
>outer jacked of the coax cable. My rule of thumb is that the sleeve
>should be 2x to 3x the diameter of the coax cable.

I figured out how to solve all of this. I took a cpvc tee, and found
that 1/2" copper pipe fits in it. I have scrap pipe, I have the tee, and
I have epoxy to keep the copper pipe in the tee. I also have a tv
antenna balun, which lost one of it's spade ends.

I'll epoxy 18" of copper pipe into each end of the tee, solder the bare
ends of that balun right to the copper pipe, and another piece of pipe
in the middle of that tee, will hold it to the house with a clamp. I
also have tv coax with ends installed, to run indoors. It wont cost me a
cent, and it's simple to do.

Since I can get a good signal outside, with the built in telescoping ant
on th radio, I am sure this will work as well or better.

I will need one thing though, I'll have to find a way to adapt the tv
antenna screw on clamp to the RCA jack on the radio. Making that may
take some doing....

[rickman]

On 3/30/2017 7:19 PM, Jeff Liebermann wrote:
> On Thu, 30 Mar 2017 16:58:57 -0500, olds...@tubes.com wrote:
>
>> This is the kind of advice I am looking for. I am not looking to spend
>> money on this. I get a a good signal from the weather service outdoors,
>> just not inside the metal building. To be sure what you are saying, I
>> think you are saying to strip back 18" of the coax. Then I should attach
>> this to something, so the center wire points toward the sky, and the
>> shield part (also 18") points toward the ground. CORRECT?
>>
>> I am already thinking I can take a 1/2" cpvc tee and two 18" pieces of
>> cpvc pipe, and shove this coax inside of it to protect it from the
>> weather. I can seal the ends of the pipe with silicone caulk. (or pipe
>> caps). I could easily attach this to my rain gutter with a C-clamp.
>
> It's called a coaxial antenna and works quite nicely. Please note
> that this is a 70 ohm antenna, not 50 ohms, which shouldn't make any
> difference for what you're doing. However, I think you run into a few
> problems:
>
> 1. You said you had some "cable TV coax" which I'll assume means
> RG-6/u. The solid center wire is good enough, but the outer shield is
> aluminum foil held together with a small amount of copper braid. When
> folding over the outer jacket, the foil is going to break and there's
> not enough copper braid to make a suitable ground element. Instead of
> RG-6/u, I suggest thicker and heavier RG-8/u.

The RG-6/U spec sheet I have says the braid is 95% coverage. That
sounds like enough to me.

> 2. There should be a small gap between the folded over braid and the
> outer jacked of the coax cable. My rule of thumb is that the sleeve
> should be 2x to 3x the diameter of the coax cable.
>
> 3. Shoving the antenna in what is called a "radome" is commonly done
> for weather proofing. If you look at similar commercial antennas, you
> might notice that they use a fiberglass radome instead of PVC. That's
> because PVC is both lossy and will detune the antenna, lowering its
> frequency. The degree to which PVC moves the resonant frequency of
> the antenna varies with PVC dimensions, thickness, and construction.
> Last time I did that, I had about a 10MHz drop at 146MHz or about 7%.
> You can compensate by cutting your driven element 7% shorter and/or
> check the resonant frequency with an antenna analyzer (MFJ-259). If
> you want to check if your material is lossy, just put it in the
> microwave oven for a few seconds and see if it gets warm. If it stays
> stone cold, it's suitable for a radome. If it gets warm, it will eat
> some RF.

Not always a reliable test. RF absorption varies with frequency,
sometimes very significantly. Microwaves are 2.4 GHz, no?

> 4. If weather proofing is a must, such antennas are often filled with
> some kind of expanding foam. I tried it with urethane foam and
> urethane insulation foam.
> <https://www.amazon.com/Liquid-Urethane-Foam-Density-Quart/dp/B007V231P6>
> Both worked, but again lowered the resonant frequency of the antenna.
> Worse, the amount was totally dependent on the density of the foam. I
> could make urethane sorta work, but it wasn't worth the exercise
> because there was no easy way to rework the results. Might as well
> not fill the radome and add some drain holes in the bottom.
>
> 5. You probably don't need a decoupling sleeve to keep the feed line
> coax from becoming part of the antenna, but it wouldn't hurt.
> <http://4.bp.blogspot.com/-6yN9hSYx2n4/UggVwPp7hlI/AAAAAAAAAgA/RAIlUyX8PAo/s1600/Coax+Dipole+Diagram.jpg>
> <http://kr7w.blogspot.com/2013/08/coaxial-dipole-for-portable-backpack.html>
>
> Personally, I think it's easier and better to just build an SO-239
> ground plane antenna and forget about the radome.
>
>


--

Rick C

[Jeff Liebermann]

On Fri, 31 Mar 2017 14:07:48 -0400, rickman <gnu...@gmail.com> wrote:

>On 3/30/2017 7:19 PM, Jeff Liebermann wrote:

>> 1. You said you had some "cable TV coax" which I'll assume means
>> RG-6/u. The solid center wire is good enough, but the outer shield is
>> aluminum foil held together with a small amount of copper braid. When
>> folding over the outer jacket, the foil is going to break and there's
>> not enough copper braid to make a suitable ground element. Instead of
>> RG-6/u, I suggest thicker and heavier RG-8/u.

>The RG-6/U spec sheet I have says the braid is 95% coverage. That
>sounds like enough to me.

It depends on the type of RG-6/u. Lots of creativity and variations
in quality:
<https://en.wikipedia.org/wiki/RG-6>
CATV distribution coax typically has a copper-clad steel
(CCS) center conductor and a combination aluminum foil/aluminum
braid shield, typically with low coverage (about 60%).
RG-6 type cables are also used in professional video applications,
carrying either base band analog video signals or serial digital
interface (SDI) signals; in these applications, the center
conductor is ordinarily solid copper, the shielding is much
heavier (typically aluminum foil/95% copper braid), and
tolerances are more tightly controlled, to improve impedance
stability.
So, if you're lucky enough to find the better cables, 95% coverage is
enough for a decent coaxial antenna. If you're stuck with the
consumer junk cable, 60% is barely enough and I've seen less.

>Not always a reliable test. RF absorption varies with frequency,
>sometimes very significantly. Microwaves are 2.4 GHz, no?

Consumer microwave ovens run at 2.4GHz. My test is not very reliable
because the dissipation factor (loss tangent) varies with frequency.
Other factors like exposure duration and oven power also have an
effect. Even commercial fiberglass antenna radomes get slightly warm.
However, I have been fooled. I decided that since polypropylene
(Plastic #5) is microwave safe, it should also make a good radome
material. Well, in thin sheets used for microwave TV dinners, it
works just fine. In thick slabs, it gets hot. Oops.

If you're worried about absorption at 162MHz (wx band), just take a
length of PVC pipe, and slide it over the antenna on a scanner or
receiver. If there's a noticeable drop in receive signal, it's not a
suitable material.

Also, carbon doped paints can also be a problem. When in doubt, use
the microwave oven test.

Extra credit. Put a piece of unclad PCB material (G10/FR10) in the
microwave oven and watch what happens. At 2.4GHz, they do get warm,
but are not very lossy and probably good enough. There are better
materials:
<http://www.microwavejournal.com/blogs/1-rog-blog/post/20436-digging-deeper-into-dissipation-factor>

[rickman]

The stuff I've bought was solid copper inner conductor, so I guess if
they are providing that, they don't scrimp on the shield.

> Extra credit. Put a piece of unclad PCB material (G10/FR10) in the
> microwave oven and watch what happens. At 2.4GHz, they do get warm,
> but are not very lossy and probably good enough. There are better
> materials:
> <http://www.microwavejournal.com/blogs/1-rog-blog/post/20436-digging-deeper-into-dissipation-factor>

Terms like "not very lossy" depend greatly on context. It may not
matter so much in a standard radio or TV application, but in other
applications where the power is very high or the received signals are
very weak even a moderately lossy material like PVC or PCB material will
make a large difference.

--

Rick C

[olds...@tubes.com]

On Fri, 31 Mar 2017 12:02:36 -0700, Jeff Liebermann <je...@cruzio.com>
wrote:

>Consumer microwave ovens run at 2.4GHz. My test is not very reliable
>because the dissipation factor (loss tangent) varies with frequency.
>Other factors like exposure duration and oven power also have an
>effect. Even commercial fiberglass antenna radomes get slightly warm.
>However, I have been fooled. I decided that since polypropylene
>(Plastic #5) is microwave safe, it should also make a good radome
>material. Well, in thin sheets used for microwave TV dinners, it
>works just fine. In thick slabs, it gets hot. Oops.

I once stuck a dinner plate in the microwave. When I grabbed it, I
burned my fingers. The plate was hotter than the food on it. It was made
of some sort of Malamine (something like that), plastic. Needless to
say, that plate never got used in the MW again.

[Carl Ijames]

"Jeff Liebermann" wrote in message
news:5a8tdctfesm7uifc8...@4ax.com...

So, if you're lucky enough to find the better cables, 95% coverage is
enough for a decent coaxial antenna. If you're stuck with the
consumer junk cable, 60% is barely enough and I've seen less.

===========================================================================

Just curious. Could you strip back the braid like you described earlier,
then slide the RG6 into an 18" piece of 5/8 or 3/4" copper tube or pipe,
stretch the braid over the top end of the pipe, clamp or solder braid to
pipe, and just cut off the excess braid? That gives you full shielding if
you have the low coverage RG6. If centering is important you could press
and glue in three wedges at the top before you fold over the braid, and
three more wedges at the bottom.

-----
Regards,
Carl Ijames

[Jeff Liebermann]

On Fri, 31 Mar 2017 15:56:35 -0500, olds...@tubes.com wrote:

>I once stuck a dinner plate in the microwave. When I grabbed it, I
>burned my fingers. The plate was hotter than the food on it. It was made
>of some sort of Malamine (something like that), plastic. Needless to
>say, that plate never got used in the MW again.

I did the same thing once (and only once). Ouch.

You're also not going to make coil forms and antenna insulators from
Melamine:
<https://answers.yahoo.com/question/index?qid=20090323002400AAXkO6n>
<https://en.wikipedia.org/wiki/Melamine>

[Jeff Liebermann]

On Fri, 31 Mar 2017 18:09:19 -0400, "Carl Ijames"
<Xcarl....@Zverizon.net> wrote:

>"Jeff Liebermann" wrote in message
>news:5a8tdctfesm7uifc8...@4ax.com...
>So, if you're lucky enough to find the better cables, 95% coverage is
>enough for a decent coaxial antenna. If you're stuck with the
>consumer junk cable, 60% is barely enough and I've seen less.
>===========================================================================

>Just curious. Could you strip back the braid like you described earlier,
>then slide the RG6 into an 18" piece of 5/8 or 3/4" copper tube or pipe,
>stretch the braid over the top end of the pipe, clamp or solder braid to
>pipe, and just cut off the excess braid?
>That gives you full shielding if you have the low coverage RG6.

Yep. That's the way it's commonly done, only it's cheaper and easier
to use hobby grade brass tubing for the ground sleeve. Something like
this:
<http://www.mictronics.de/blog_content/_uploads_/2009/12/Coaxial_antenna.jpg>
The common 2.4Ghz Wi-Fi rubber ducky antenna is built much the same
way:
<http://802.11junk.com/jeffl/antennas/coaxial/coax-ant.jpg>
I would put a brass washer over the cable jacket, push the braid
through the hole, spread it out across the washer, solder, and then
solder on the brass tube. Then, make a conical pile of RTV or other
sealant to shed water and keep it out of the coax cable.

However, if you want to be really cheap (like me), use aluminum duct
tape for the ground sleeve. I add a few layers of PEX tubing over the
RG-6/u to increase the diameter and to seperate the duct tape sleeve
from the coax braid. The aluminum duct tape goes over the outside of
the tubing. The braid and foil go over the aluminum duct tape, and
another layer of aluminum duct tape is added to hold the braid in
place and to provide an electrical connection.
<https://www.walmart.com/ip/Duck-Brand-HVAC-Aluminum-Foil-Tape/26977961>

>If centering is important you could press
>and glue in three wedges at the top before you fold over the braid, and
>three more wedges at the bottom.

That would work, but I like the brass washer idea better or just glue
everything inplace with RTV, hot melt glue, or whatever falls off the
shelf.

With antennas, the uglier it looks, the better it works.

>Regards,
>Carl Ijames

[Jeff Liebermann]

On Fri, 31 Mar 2017 16:05:14 -0400, rickman <gnu...@gmail.com> wrote:

>The stuff I've bought was solid copper inner conductor, so I guess if
>they are providing that, they don't scrimp on the shield.

Are you sure? Use a magnet to check. I just cut off a piece of the
center wire from some junk RG6 coax. The center wire looks like it's
all copper, even after I cut it with diagonal cutters several times.
However, a magnet tells the real story by sticking to the wire. It's
copper plated steel.

Might as well play with the braid:
<http://www.802.11junk.com/jeffl/crud/RG6-junk-coax.jpg>
What I did was strip back the jacket to expose the braid. I then
shoved a piece of post it note paper under the braid so we can see the
braid without the foil background. I then pulled it tight so as not
to increase the diameter (much) and taped the end to hold the mess in
place. Notice the rather large gaps between the strands in the braid.
My guess(tm) is about 40% coverage.

The markings in the cable are:
RG6 HIGH PERFORMANCE 2.25 GHZ DIGITAL CABLE E236426 18AWG UL
c(UL) (CM) 75°C W/O 0606 0094ft

>> Extra credit. Put a piece of unclad PCB material (G10/FR10) in the
>> microwave oven and watch what happens. At 2.4GHz, they do get warm,
>> but are not very lossy and probably good enough. There are better
>> materials:
>> <http://www.microwavejournal.com/blogs/1-rog-blog/post/20436-digging-deeper-into-dissipation-factor>

>Terms like "not very lossy" depend greatly on context. It may not
>matter so much in a standard radio or TV application, but in other
>applications where the power is very high or the received signals are
>very weak even a moderately lossy material like PVC or PCB material will
>make a large difference.

Agreed. I started this by mentioning that PVC will detune and move
the resonance point of a VHF antenna, and may add a little loss.
Neither problem is particularly critical for a low gain VHF receive
only antenna. PVC will work, but fiberglass will work better.

[Michael A. Terrell]

http://www.hamuniverse.com/2metergp.html

--
Never piss off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)