How to make a simple outdoor antenna for a Weather Radio

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????

Reply to
oldschool
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I'd search for VHF antenna.

Reply to
tabbypurr

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

Reply to
sdy

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.
Reply to
artie

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.

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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.

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Or you can just buy one.

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

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

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Rick C
Reply to
rickman

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

Dan

Reply to
dcaster

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

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

The NWS VHF signals are vertical polarized.

Reply to
tom

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

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Rick C
Reply to
rickman

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.

Reply to
John S

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.

vertical folded dipole.

image:

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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:

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Reply to
Jasen Betts

Maker and model please?

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.

That's a common problem. Look into proper cable entries first. For example:

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.

Find an SO-239 connector and build a simple ground plane. Lots of ways to do it: 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.

See above.

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.

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:

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: One catch is that it will be directional so cut the slot on the correct side of the building.

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.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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.

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-TV
Reply to
Tauno Voipio

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.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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.

Reply to
oldschool

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

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 ma ss-produced. You might find a commercial-grade model that has much better receiver sensitivity -- but I gather from your post that no funds are prese ntly allocated to the effort. Best of luck!

Reply to
mpm

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....

Reply to
oldschool

It depends on the type of RG-6/u. Lots of creativity and variations in quality: 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.

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:

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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.

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.

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Rick C
Reply to
rickman

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.

Reply to
oldschool

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

Reply to
Carl Ijames

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