Topic: External Antenna for WMR100

[gadget_guy]

I've always had reception problems with my WMR100 console.  Periodically I would lose contact witht he outdoor sensors.  I finally decided to attach an external antenna.  Luckily I fouond good instructions on taking apart the console.  Here is the link:

http://www.weather-watch.com/smf/index.php/topic,44575.15.html

Once the console was apart, I unsoldered the internal antenna.  I used a small piece of coax to bring the connection outside of the console so I could attach a connector.  Temporarily, I'm using a metal shielded RCA plug and jack pair.  I'm sure this is not optimal and will replace it soon with a better connector.  The antenna is a home made dipole consisting of two pieces of wire approximately 6.4 inches long.  the center conductor and shield were each soldered to one piece.  The pieces were mounted on a small piece of acrylic plastic. 

I mounted the dipole in a basement window and get solid reception.  It was a mod well worth doing.

[gadget_guy]

I've been running the WMR100 with an external antenna for a week now.  Hasn't lost contact with the outdoor sensors for a moment.  It was a modification well worth making.  Now I can keep the console where I want it, not where it barely gets a signal.

[RVGregoryZ]

Thank you So Much for the link. 

[gadget_guy]

My pleasure.  Hope it works as good for you as it did for me.

[aweatherguy]

Not sure how much difference this makes -- perhaps not a lot since most folks seem to report good results.

There is a small circuit at the antenna terminals in the WMR100 called a "balun" -- it converts the signal from a "balanced" antenna to the "un-balanced" input of the WMR100's wireless receiver. And a dipole is a "balanced" antenna so this is a good setup.

Coax is an "un-balanced" transmission line. When you put a piece of coax between the WMR100's inputs and an external dipole antenna, the outer shield of the coax actually becomes part of the antenna, and it can end up making a difference where and how you route the coax and how long the coax is.

To avoid this issue, you would use a "balanced" transmission line instead of the coax -- this could be a simple as a pair of insulated wires twisted around each other just barely enough to keep them together -- don't over-twist. Anything from 18 to 26 gauge wire with some kind of plastic insulation should do the job. There's more details here like what the effective impedance of the twisted wires is and so on, but it is probably not worth worrying about -- as long as the wires' insulation is in contact with one another over the complete length, the impedance shouldn't be all that bad.

Anyway, if you're having any issues with the reception using a piece of coax you could try the "twisted-pair" approach instead. If the coax setup is more convenient, I would still try that first since folks seem to be having good luck with it...

[aweatherguy]

Based on several other postings, here's another mod that is working pretty well for me. It has the advantage of not requiring connectors, coaxial cables or separately mounted antenna elements. It only requires drilling one small hole in the housing and can be removed with little aesthetic damage to the WMR100.

This modification is pretty painless, too. All you need are the tools to disassemble the WMR100 as posted elsewhere, a 1/16th inch drill bit and about 18 inches or so of 14-gauge copper wire. Here are the steps I followed in making this modification:

1) Disassemble the WMR100.

2) Cut the upper antenna element off about 2 inches above the point where it is soldered into the WMR100's circuit board. Remove the upper antenna segment (with the coiled end) and discard.

3) Drill a 1/16th inch hole in the top of the front half of the plastic housing.

4) Strip enough insulation from the copper wire so it can fit through the hole and overlap with the remaining antenna element for soldering. You could also use bare (non-insulated) copper wire and skip this step.

5) Insert the copper wire through the hole in the top of the plastic housing and solder to the remaining antenna element. Two notes here -- the antenna element seems to be steel and does not accept solder very well so you could replace that short piece with some 18 or 20-gauge copper wire (just be careful to bend it like the original wire so it does not interfere with the plastic case during re-assembly. I tried soldering the 14-gauge wire directly to the antenna terminal on the circuit board, but it is too large and interfered with re-assembly of the housing. Also, you can see where I accidentally touched the plastic case with the soldering iron and melted it a bit so watch out for that.

6) Cut the copper wire to length -- the distance from the connection at the circuit board to the tip of the antenna should be about 18 inches (give or take 1/4 inch).

7) Re-assemble the WMR100. Done.

Optionally, you could skip step (2) and simply solder the copper wire to the existing antenna element. I don't know how well this would work but might be worth trying because it leaves the original antenna intact. If you find the reception less than ideal, you could try trimming as much as 1-1/2 to 2 inches from the top of the copper wire in 1/4 inch increments. Theoretically, the "ideal" length is around 17 inches but your mileage may vary (see hand-waving below).

Here is the idea behind this. The upper section of the antenna is now about 5/8 wavelengths long at 433.92MHz. A common antenna design is a 5/8 wavelength vertical wire mounted on top of a large ground plane. This design has the 5/8 wavelength vertical wire, but substitutes the existing lower dipole section for the ground plane. Okay, so this design is just plain odd in terms of commonly used antenna designs.

<hand-waving>The presence of the large WMR100 circuit board in such close proximity to the antenna makes the analysis/simulation of this antenna (before OR after modification) extremely difficult. As is often the case in the world of antennas, sometimes an antenna just works and it is not worth the trouble to figure out why.</hand-waving> As a result, it is reasonable to conclude that there may be other wire lengths that work even better so don't hesitate to experiment.

[gadget_guy]

Your method should also give pretty good results.  The only reason I used the dipole and a length of coax is to give me the ability to locate the antenna in a spot where I had good reception (read:  near a window) The dwelling wher the console is located had foil backed insulation shich I'm guessing compiunded reception problems.

[aweatherguy]

Good point. Each of these two modifications will be attractive in different situations. If only OS would do something like this...but I guess that dead horse has already been beaten beyond recognition.

[bobkeenan]

Just wanted to let you know that I too was having problems with sensor drop outs.   So I tried your directions.   It was a little scary pulling the glued gray plastic from the silver but eventually I got it.   I assumed that I would not be able to solder the new copper antenna to the steel and opted to pull out the vertical portion of the existing steel antenna.   It did not want to come out as the end of it had been twisted below the circuit board.   So to get at that I had to take out another  8 or so screws.   It was tricky but I got it out.   My next problem was that the copper wire I chose to use was from a coax cable with removed insulation.  The diameter of that was just a little larger than the hole in the circuit board.   I risked opening up the hole a bit.  I then bent the end of the copper wire to match (sort of) the existing steel wire antenna.  That took some work.  Soldering went fine.  Re- Assembly was a breeze.  Plugged it in.  Wha.... Laaa.... seeems to work like a charm.... no dropout anymore!!.   I left the whole length of the copper wire from joint to tip at 18".  I wish there was a way to measure signal strength.    So I don't know if I am at an optimal length.

Based on several other postings, here's another mod that is working pretty well for me. It has the advantage of not requiring connectors, coaxial cables or separately mounted antenna elements. It only requires drilling one small hole in the housing and can be removed with little aesthetic damage to the WMR100.

This modification is pretty painless, too. All you need are the tools to disassemble the WMR100 as posted elsewhere, a 1/16th inch drill bit and about 18 inches or so of 14-gauge copper wire. Here are the steps I followed in making this modification:

1) Disassemble the WMR100.

2) Cut the upper antenna element off about 2 inches above the point where it is soldered into the WMR100's circuit board. Remove the upper antenna segment (with the coiled end) and discard.

3) Drill a 1/16th inch hole in the top of the front half of the plastic housing.

4) Strip enough insulation from the copper wire so it can fit through the hole and overlap with the remaining antenna element for soldering. You could also use bare (non-insulated) copper wire and skip this step.

5) Insert the copper wire through the hole in the top of the plastic housing and solder to the remaining antenna element. Two notes here -- the antenna element seems to be steel and does not accept solder very well so you could replace that short piece with some 18 or 20-gauge copper wire (just be careful to bend it like the original wire so it does not interfere with the plastic case during re-assembly. I tried soldering the 14-gauge wire directly to the antenna terminal on the circuit board, but it is too large and interfered with re-assembly of the housing. Also, you can see where I accidentally touched the plastic case with the soldering iron and melted it a bit so watch out for that.

6) Cut the copper wire to length -- the distance from the connection at the circuit board to the tip of the antenna should be about 18 inches (give or take 1/4 inch).

7) Re-assemble the WMR100. Done.

Optionally, you could skip step (2) and simply solder the copper wire to the existing antenna element. I don't know how well this would work but might be worth trying because it leaves the original antenna intact. If you find the reception less than ideal, you could try trimming as much as 1-1/2 to 2 inches from the top of the copper wire in 1/4 inch increments. Theoretically, the "ideal" length is around 17 inches but your mileage may vary (see hand-waving below).

Here is the idea behind this. The upper section of the antenna is now about 5/8 wavelengths long at 433.92MHz. A common antenna design is a 5/8 wavelength vertical wire mounted on top of a large ground plane. This design has the 5/8 wavelength vertical wire, but substitutes the existing lower dipole section for the ground plane. Okay, so this design is just plain odd in terms of commonly used antenna designs.

<hand-waving>The presence of the large WMR100 circuit board in such close proximity to the antenna makes the analysis/simulation of this antenna (before OR after modification) extremely difficult. As is often the case in the world of antennas, sometimes an antenna just works and it is not worth the trouble to figure out why.</hand-waving> As a result, it is reasonable to conclude that there may be other wire lengths that work even better so don't hesitate to experiment.

[LuckeyJim]

Old topic, I know. I just did this myself and highly recommed it. It made all the difference, now all my sensors are rock solid with no dropouts.

I went with a quarter wavelength, 17.3 cm. I used a piece of insulated solid 14 gauge wire from the hardware store, the kind used as ground wire for house wiring. I cut off the top section of the old antenna, close to the circuit board, then hot glued the new wire into place. I used a hacksaw to cut a notch in each half of the case, at the top, for the wire to pass through. I soldered a short piece of thin copper wire (about 22 ga) to the antenna wire, and soledered the other end of it to the circuit board. Reassembled and it worked great. Total time maybe an hour.

When I removed the front window to get at the screws, it was pretty solidly glued. Just keep prying, it will come off. You don't need to re-glue, the old glue is sticky enough to hold the window when you put it back on.