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Yagi Antenna Question Answered January 2012

I live where cellular reception is poor, and I depend on a cellular modem, amplifier, and Yagi antenna (Wilson Electronics 301111) mounted on our chimney for an Internet connection. In the summer it works pretty well, but in the rainy winter, the signal deteriorates significantly and our connection speed drops. If we're using the fireplace, and the weather dries out for a few days, the signal improves. However, if it's rainy but we're not using our fireplace for a few days, the signal also improves.


My best guess as to the reason is that the combination of smoke from our fireplace and moisture from rain or dew are coating the antenna with a film that is conductive enough to create a partial short across elements of the antenna, causing some attenuation of the signal. The antenna is mounted about six or seven feet above the chimney cap, and it's not really practical to mount it higher without going to a much more complicated mast setup with guy wires.


I'd like to know if I can spray some insulating coating on the Yagi antenna that will prevent the film contacting the conductive parts of the antenna, but that also will not in itself attenuate the signal. Something like WD-40 might work for a while — causing water to just run off — but I want something more permanent, like maybe liquid tape that hardens into a rubbery coating. I just don't know if that type of coating might in itself attenuate the signal.


Does anybody have any advice on how I could seal my antenna without attenuating the signal by an appreciable amount? I'm also open to other ideas, except to go to a different connection technology (DSL isn't available, T1 is too expensive, satellite is worse than what we've got now).

#1125
Gary Rathbun
Placerville, CA



Answers

Hi, Gary! I am a ham (amateur radio operator) and here is what I know about Yagi antennas (actually Yagi-Udi antennas, but that's a story for a different time).


I would advise against WD40, as it will almost certainly mess up the impedance where it matters (at the driven element). But first, a bit about Yagis.


A yagi antenna is constructed such that the center point of all the elements (other than the driven element) is grounded to the mast. So shorting the elements to the mast is done at the factory for all but the driven element.


The driven element is the one that connects (usually via some sort of matching network) to the coax, and my bet is that THAT is where you need to focus your attention.


Also, there are affects on the antenna from 'nearby' objects, including 'ground' (or anything horizontal below (or even above) the line of sight of the antenna). If the 'nearby' objects are enough wavelengths away from the antenna and not in the 'line of sight' then their impact should be minimal.


However, 'ground effects' can be helpful or hurtful, even out to multiple wavelengths away from the antenna. This is where 'higher is better' comes from. By the way, the higher the antenna is above 'ground' the better the antenna works.  However, if you mount an antenna higher above the earth, but your rooftop is in the line of sight to your other antenna, your 'ground level' is the roof, not the ground you walk on! (Especially at the frequencies we are talking about here).  So, all other things being equal, it is better to put the antenna on the side of the house closest to the antenna you are 'talking to'.


For more information, I recommend the ARRL Antenna Book.


Anyway, back to the question:
There are a few places where you are likely to lose signal strength:


1 - At the end of the coax, or inside the end of the coax. If water gets into the coax, it will change the characteristics of the coax such that you WILL lose (lots of) signal strength. If the coax terminates in a connector of some kind, then you want to protect the connector from water. If the coax does not terminate in a connector, then does it end such that the wire angles DOWN to the end of the coax or up? If up, then you have a great place for water to get in to the coax. If possible, orient the coax such that water on the coax will not travel toward the open end of the coax. In either case, protect the end of the coax, and all connections, with something non-'conductive' at RF (at microwave, to be more precise). Either some sort of silicone sealer, or use a plastic margarine tub or similar (assuming the antenna is far enough from the chimney to avoid melting the plastic!). Before using a sealant, make sure it is not conductive at microwaves (PVC is notorious for being conductive there). If in doubt, one partial test is to place some of the material, along with a cup of water, in a microwave and cook for a while (start with a few seconds, if the material in question does not get hot, go for longer). If the material will 'bother' your antenna then it will likely get hot (or at least warm) in the microwave. Do this same experiment with your margarine tub also!


2 - At the matching circuit. What sort of matching circuit is being used will determine how easily affected it will be by water and  so forth, but generally the matching circuit wants to be dry. Some stay drier by design than others. In any case, the margarine tub from 1 could probably be placed over the entire driven element and coax end. Another possibility would be to build a 'roof' for the antenna, but if you use metal or anything affected by microwaves (see experiment in 1 above), then you need to keep it a reasonable number of wavelengths away from the antenna.  Since we are talking microwaves, or at least 900MHz, then that isn't so bad as trying to build a roof for an HF antenna! If I remember correctly, 5 to 10 wavelengths away should be more than adequate. At this point, I should recommend the ARRL antenna book, as it has MUCH more info, including the frequency to wavelength formula and how far you should put the 'roof.' You might get away with 1 to 2 wavelengths away, IF the 'roof' is not resonant at the frequencies of your internet provider. This is where the ARRL Antenna Book is probably your best bet.


3 - At any point between the antenna and the receiver where water can enter the coax.


Since you say that the fireplace seems to exacerbate the issue, then you probably have a combination of soot/whatever plus water in the matching circuit, coax, or both.


Random ideas and thoughts:
Can you move the antenna further from the chimney?


Perhaps you need to shield the antenna from the smoke as well as from the rain.


Rather than moving the antenna higher, is there anywhere else where you still have line of sight to the cell tower (or whatever is the other end of your radio circuit)? In other words, if you could protect the water-sensitive areas of the antenna, AND move it to where it does not pick up 'stuff' from the chimney that would be a win-win. One concern is  water dissolving stuff from the fire that then attacks and corrodes the antenna!


Given that we are working with at least 900MHz, as long as you have line of sight to the other antenna, anywhere on your roof should be almost as good as anywhere else. In fact, if you have a clearer shot 6 feet lower, then 6 feet lower is better, as long as you don't move your roof, (or neighbors roof), into the 'ground effect' area) So, if you can mount the antenna away from the fireplace and still get a good signal, that's probably better all the way around. In fact, as I say, start out with the side of the house closest to the other antenna.


Bottom line: weatherproof the coax, especially the ends; protect the matching circuit from excessive water; keep the exhaust from the chimney from mixing with water and depositing on the antenna (possibly by moving the antenna elsewhere).

Rusty Carruth
Tempe, AZ

Water combined chemicals in smoke from a fireplace could get into connectors and cause signal loss in Gary Rathburn's antenna system. He notes, "If it's rainy and we're not using our fireplace for a few days, the signal also improves."  Perhaps the rainwater by itself flushes some soluble chemicals out of the connectors. It's unlikely water on the antenna or rain droplets cause a problem.


During a dry period, wrap exposed connectors with Coax-Seal or Scotch-brand "2228 Moisture Sealing Electrical Tape." Better yet, replace the connectors and the cable and then seal the new connectors. If moisture and chemicals from smoke got into a connector, they probably got into the cable too. Also, always create a drip loop to keep water from running down cables and into connectors.


If you try to "seal" the antenna, you can de-tune it and cause signal loss. Antennas are manufactured to work outdoors in bad weather.

Jon Titus, KZ1G
Herriman, UT

Yes, fire makes carbon smoke a conductive. I'd try a plastic bag to see if it corrects it. Or, place a shield one foot under the antenna.

Richard Lenker
via email

I suggest you try wrapping the elements of your Yagi antenna with PVC electrical tape. It might protect the antenna enough to provide the necessary improvement. As a young "shop gopher" in a two-way radio shop, I earned many hours of minimum wage wrapping two-way base station antennas with electrical tape. The owner of the shop insisted it reduced received noise and extended the life of the antenna.

Don Pitchford W9EBK
via email

It sounds like you have a faulty cable and/or cable connector at the antenna. I would replace the cable with Wilson 400 low-loss cable, and put a boot on the connection at the antenna to keep out moisture.


Additionally, the Wilson 301111 Yagi is quite directional; try aiming.


If it has been several years since you installed the antenna, maybe more cell towers have been built in your area.

wave2003
via email

I think you should look at the connectors. They may not be water tight!


Electrical duct butter, electrical duct seal, and coax seal can all be used to encapsulate the connector and socket area to seal it from water inclusion.


I’ve used Beam antennas up in the air for decades with good results.

B Jim Russell N4ICU
via email


Modify Scott 340A Tube Receiver Answered July 2012

I live very close to a huge water tank that affects stereo reception. I would like to connect a scope to measure FM multipath distortion. I have had no luck getting help from user groups, etc., so far! Does anyone know exactly how to do this? I can't afford the McIntosh tuners. I can do the construction if I had a schematic. Is this possible?

#7121
Nick Oshana
Bristol, CT



Answers

The first place I saw the oscilloscope multipath display was on the Marantz 10b. Two other FM tuners with the scope outputs were the Scott 312 (and the Scott 312b, plus the kit versions LT112 and LT-112b) and the Heathkit AJ-15 (and the receiver version AR-15). You need an X-Y oscilloscope — preferably with response down to DC. Connect the horizontal X input to the output from the audio detector (still monophonic, not yet demultiplexed) and connect the vertical Y input to the AGC (automatic gain control) signal.

Joseph Feng
via email


Half Cycle Magnetizer Answered January 2012

I'm looking for a half cycle magnetizer schematic for 60 cycle, 120 volts. I used one at work before I retired, but it was built for a higher industrial voltage. I would like to build one from scratch using the standard 120 volt line. I know that it must be contained in a protective box, takes many turns of transformer windings, and uses a high speed thyristor.

#11210
Bob Macias
Fernandina Beach, FL



Answers

Check out the Oersted Technology article at http://oersted.com/magnetizing.PDF.

Peter A. Goodwin
Rockport, MA


Extra Bright Picture/Exit Bulb Answered January 2012

I'm looking for help locating or building a super bright exit/picture/display style bulb with an E26 base for my mom.

My 95 year old mother has macular degeneration in both eyes. She still enjoys reading but finds it harder by the day. Her main complaint is that she can't get enough light on the printed page.

I'm asking for help to locate and/or build a bulb with what I know as ultra-bright LEDs. It will throw the equivalent of 200 [fairly cold] incandescent watts of light down onto her page. I'm no engineer, but am handy with a soldering iron and multimeter. Can anyone help me?

#1129
Rod Reynolds
Bowie, MD



Answers

I'm reading between the lines here,  so I apologize up front if I'm in the wrong universe with my answer.

I see 2 main approaches (off the top of my head) - build an LED illumination thingy from scratch, or buy LED spotlight bulbs 'off the shelf' and fabricate whatever you need to get enough light.

Get It Off The Shelf
A fairly long search on google found all sorts of possibilities, if you only want to get some E26 base bulbs and create an array of <n> LED spotlight bulbs to supply he desired light level. If you assume your 200W incandescent bulb puts out something in the neighborhood of 3000 lumens, then you need about 7 or 8 420-lumen spots like the Grainger 3CRA2 (Optiled model 1503050217) - which Grainger sells for $45 each… Or just 3 of the 6XWKD (GE Lighting LED20P38S830/25) which puts out 1050 lumens (at $60 each) would also supply the desired light output.

If you want to go this way, google is probably your best friend. (Along with eBay). Use "LED spotlight" or "LED high-power" or "LED 20W" (or even "LED e26", which is what I started with).

Build It Yourself
Googling for 20W LEDs, I found www.hero-ledstore.com/heroled-20w-led-c-2_184.html with all the parts you'd need to make a 20W LED lamp (but that's gonna run you about $74 and you still need 2 of them (apparently they are 1600 lumens each). Interestingly, the parts to make a 50W (4000 lumen) 'system' are only about $175 - and you'd only need one of those… There are other options out there also, I'm sure, as a google for "high power LED" returned about 78 million hits "wink." The thing there is that you need a constant-current source to feed the LEDs with, not a constant voltage (but with voltage limits, IIRC).

Rusty Carruth
Tempe, AZ


LCD Display Help Answered January 2012

In the recent article on the web-based thermostat (Sep-Oct’11) an EA DOG-M LCD display was used. I have two of these displays and haven't been able to get them working. I use PICBASIC PRO and it seems there are a lot of people that are trying to use this LCD with some trouble. There isn't much in the way of information on the forums. Could someone please show how to initialize the display with PICBASIC PRO in both SPI and four-bit mode?

#1128
Craig
Bettendorf, IA



Answers

Camillus Blockx
KNOX


Power Supply For Fluke 8050A and 8600A January 2012

I have a couple of older Fluke 8050A and 8600A multimeters that were outfitted with battery options. The batteries are long gone and I never really used them anyway. I would like to use them as bench only meters and reconfigure them to a non-battery type supply. Does anyone have an internal power supply plan that I could use in these meters without drilling holes in the cases and cutting up traces on the circuit boards? Something using capacitors, diodes, etc., that would fit into the battery area and plug directly into the battery connections.

#1122
David Asselin
Saint-Lambert, Quebec


Autorangeing DVM Using 7101 Answered January 2012

I want a small circuit using a microcontroller to convert an analog DVM to an autoranging DVM using a 7107 IC. Or, just explain how to convert the input of a 7107 DVM to an autoranging input.

#1121
Gurdeep Singh
Delhi



Answers

Although it doesn't use a microcontroller, Intersil described a circuit for making an auto-ranging DVM in their Application Note AN046. The URL for the PDF file of this article is www.intersil.com/data/an/an046.pdf.

 

Their basic circuit (Figure 1 in the app note) is for a 7106 DVM chip which is meant to drive an LCD display and run off batteries. A modification of that circuit is required to use a 7107 chip which uses a dual supply instead of a single supply, and has a higher power drain due to the LED display needs. That modification is given at the end of the Intersil article, in the text and in Figure 8. This circuit design utilizes the over-range/under-range states of the DVM chip to trigger the auto-ranging function, so depending on your application it might be of benefit to use an improved DVM chip that incorporates a zero-integrate phase feature to improve the recovery from over-range. Some manufacturers have added zero-integrate phase to their modern versions of the 7107 (e.g., Maxim), but DVM chip versions that explicitly include this improvement include the 7136 chip (sub for the 7106) and the 7137 chip (sub for the 7107). I noticed a couple of minor typos in the Figure 1 circuit of this article. The CD4028 logic chip is mislabeled as CD402T, and both output lines are labeled as over-range ("OR") instead of one line being labeled over-range ("OR") and one being labeled under-range ("UR").

William Braell
via email


DC Reducer 48V to 12V Answered February 2012

I need a simple breadboard circuit to reduce 48 VDC to 12 VDC. I was able to create one, but did not have enough wattage to support my 12V lights and radio. I know I will need a heatsink, but any other help would be appreciated.

#2128
Bill Fitzpatrick
Pepperell, MA



Answers

After a bunch of looking, I found this on Amazon. www.amazon.com/DROK-Synchronous-Voltage-Converter-Waterproof/dp/B00J229O9A/ref=sr_1_36?ie=UTF8&qid=1418062090&sr=8-36&keywords=dc+dc+converter+Buck


You didn't say how much power you needed but, this looks pretty robust. Good Luck

Ray Perry
Jacksonville, FL


Two AC Switches, One Fan Answered February 2012

I have two different bathroom vents going into the same exhaust fan. I want to sense either or both switches to access the main relay to run the fan (kind of like an OR gate which I can make from logic gates for DC).


However, my situation calls for AC switches and fans, and I cannot think of a way without converting to DC to be able to switch the AC (long way around).


Is there a simple solution using two 110 VAC switches to turn on the exhaust fan, and then off when both switches are off?

#2124
Raj
Fairfax, VA



Answers

The problem with standard SPST switches connected in parallel, if either is left on, the other cannot turn off the fan. If the switches are connected in series, when one switch is left off, the other cannot turn on the fan. The solution is a three way switch arrangement.


This uses two SPDT switches instead of the SPST version. Either switch can turn on or off the exaust fan. If you are not familiar with 3-way switch wiring, go to your home repair store and get a book like "Home Wiring For Beginners".


There is one problem, if someone turns on the fan in the first room, someone in the second room can turn it off if they did not notice the fan was running.

Dennis Hewett
Frontenac, KS

The answer to question # 2124 "Two AC Switches, One Fan" by Stan Strom on page 80 of the March 2012 edition of Nuts and Volts will not meet the questioners needs.


The circuit shown in the figure is a neat implementation of an inverted eXclusive OR (XOR) circuit using switches. In this circuit the fan relay will activate (thus turning the fan ON) when BOTH switches are in the ON position or BOTH switches are in the OFF position (XOR output is high if either input is high BUT not both inputs high). With the switches in opposite positions (ON-OFF states) the relay will deactivate and turn the fan OFF. [I have had students try to use switches to simulate logic gates like this. Good job Stan!]


Looking at 120 VAC bathroom fan specs, most draw 0.8 to 1.5 amps. If you have a light fixture with two (2) 60-watt bulbs, they will draw 1 amp. The 14-gage (14 AWG) wire used in most lighting circuits will handle 15 amps at 120 VAC and most lighting circuits are on 15 amp breakers. [Be sure to check that the bathroom lighting circuit is capable of handling the extra fan load just in case the installer was cutting corners]


Most vent fans are powered from a 120 VAC switch without a relay. I would locate the light fixture junction box and simply hook one 14 AWG wire from the HOT side of the lamp (its the BLACK wire if the light was wired in standard fashion, if the fan does not run when the switch id ON use the other wire at the light fixture) in each bathroom to the hot terminal of the fan. The vent fan neutral is hooked to the lighting circuit neutral. This hookup avoids using two (2) extra switches and a relay. One of the tenets of reliability says: "The more parts in a circuit, the more probable the system will fail." A tenet of economics says: "The more parts in a circuit, the more the circuit will cost."


If you want separate switches for the fans and lights, just wire the fan switches like the light switches but run the HOT wires from the fan switches to the HOT terminal of the vent fan. Two switches in parallel turned ON at the same time will not hurt anything, they will each carry half of the fan motor's current.


The original question mentioned using logic gates. The logic circuit would be simple: Hook the HOT wires from the light switch to the OR gate inputs through a device that converts 120 VAC to logic level voltage (e.g, an opto-isolator) and hook the OR gate output to the vent fan  HOT terminal through a relay (logic voltage rated coil and 120 VAC rated Normally Open contacts). This circuit would have a reduced reliability and higher cost due to the high parts count. Engineers try to minimize parts count whenever possible.


On the mechanical side, be sure to vent the bathroom fan's exhaust to the outside to avoid mold and mildew in the attic. Also check all electrical and building codes to make sure you do not anger the "regulatory gods."


Sorry for the wordiness but engineers try to cover all of the possibilities.

Tim Brown
Honea Path, SC

All that is necessary to make two switches control a single relay for your bathroom fans are two single pole double throw switches. They're very often sold as three-way switches for controlling a lamp with two switches and are readily available at Lowes or Home Depot.


Feed the hot line (the black mains wire) to the common terminal of one of the switches; the two legs of the switches connect to one another — these are called 'traveler' lines. The relay connects between the common of the second switch and the neutral line (white mains wire).


Using the circuit below, if the relay is energized, then flipping either switch will turn it off. Then with the relay off, flipping either switch will turn it on. It is shown in the on position.

Stan Strom
via email

Maybe I'm missing your intent, but it seems you should be able to just wire two 120 VAC switches in parallel.  Either OR both switches on will turn on the fan.  Both switches off will turn off the fan.

Daryl Reece
Atlanta, GA

I can see no reason not to connect two switches to one fan, that is, in parallel, as long as you check that the same circuit provides the "hot" lead to each switch. The US standard is Up = On, so it would be relatively easy to see which switch was used to turn on the fan.


If you are rewiring anyway, I would use single pole double throw switches as they are used when controlling a light with two or more switches. Then flipping any one of the switches will change the mode off to on or on to off. This requires that some of the cables have a third conductor known as a traveler.

Andrew Eliason
Mashpee, MA

If I understand this, then all you need are 2 three-way wall switches. One at each location of the two vents and then either switch will control the fan.

B Jim Russell N4ICU
via email

A simple solution is to use a three-way switch at each of the two locations (connected with a 3 wire cable) to control the Fan. Most wall switches are “single pole, single throw”. Outwardly, three-way wall switches” look the same, however they are single pole, double throw. Analogous to your situation, a common three-way switch use is to have one at the top & one at the bottom of a stair connected to control a light on the stairway.


Three-way wall switches” are inexpensive, easily found at home centers, electrical and hardware stores. The wiring is not complicated and there are many Internet sites for details, e.g., www.electrical-online.com/electrical/diagrams/

Ray M
Surf City, NJ

We have three bathrooms and one exhaust fan which is ducted to all three rooms. Our solution was to use a double pole switch in each room (commonly available in regular toggle wall switch format) where one pole does the lights in that room, and the other pole is wired in parallel with the second pole of the other two switches, and then to the fan motor, so that if any of the three switches is turned on, the fan runs, as well as the light in only that room turns on. Be sure to take safety all precautions, and follow electrical codes, as we are dealing with 110 VAC.

John C
via email

Use two three-way AC switches. These are very commonly used for lights so two switches can control the light. It will allow switching the fan off from either location no matter which location turned it on.


The problem might be getting the wire from switch #1 to switch #2 but since they both control the same fan there should be a way to get the needed wire from one to the other.


The switch instructions that should come along with them, or a good "How To" book will show how to wire them up correctly.

Philip Karras KE3FL
via email


Multi Output Power Supply Answered January 2012

I want to know the simplest solution for this power supply need. My input is 36-75 DC.
I need these outputs:
+-65V @ 70 ma
+5V @ 200 ma
+-15V @ 150 ma

#1123
Ali Asadzadeh
Shiraz, Fars



Answers

First, you won't find (as far as I can tell) any negative regulators that will take more than -40V input. Indeed, you will have trouble finding ANY regulator (positive or negative) that will take 36 to 75 VDC input.


So, since it appears that you have only +35 to +75 VDC available, I recommend something like the MIC28500 switching regulator (Digi-Key has them; http://search.digikey.com/us/en/products/MIC28500YJL%20TR/576-3969-2-ND/2764089note that these are surface-mount deals ... sorry!) to provide something in a voltage range that is easier for other regulators to handle (or you could just use two of those for the five and 6.5 volt outputs, and one for supplying the other regulators — note that one of these things can supply up to four amps!). So, I'd say:
• One MIC28500 for the +5V
• One MIC28500 for the +6.5V
• One MIC28500 supplying +12V (its max output) to the following:
Some sort of switching inverting regulators (like the LT3483 or similar) to convert the +12V to -6.5V, and -15V outputs.


Another switching regulator to boost the 12V to 15V, for example, something like the LM2574N.


If the MIC28500 chips are too expensive, you could just use one to supply +12V and choose other regulators from there (for example, an old run of the mill 7805 or 78L05 for the 5V).

 

I found all the above regulators by going to digikey.com and searching for 'voltage regulator IC.'

 

On the other hand, you could drop the voltage down to something easier for 'normal' voltage regulator ICs to handle using a resistor and a zener diode. So, you'd have a resistor of proper wattage and resistance in series with a 20V (for example) zener. Allowing for 2A of current (assuming we end up using inefficient linear regulators here, since the load is only 640 mA max) with an input voltage of 80V and an output of 20V, we need to drop 60V in that resistor at 2A, or 120 watts. Ouch! That's nuts! So, let's go back to the MIC28500 or similar.

 

Is there some way of getting a 'nicer' voltage input range beyond regulating it inside this power supply? That is, if you can manage to get the input voltage to a max of 30V, you greatly open up the possibilities for off-the-shelf voltage regulator ICs.


On the other hand, if you don't want to build it, I found that Acopian makes DC-DC supplies that could work — even if you just use one to convert that 36-75 range to something more friendly. The 48C5FT1000 supplies 5V and the 48C15FT400 supplies 15V, but they are pricy; about $188 each. TRC Electronics also makes such things, with various output voltages (trcelectronics.com).
 

Summary:
The options seem to me to be:
1 - Buy an off-the-shelf regulator(s), e.g., Acopian (expensive).
2 - Use some sort of down-regulator (Acopian, TRC, MIC28500, zener(!), etc.) to supply a lower voltage to the various end-user regulators, then have some number
(probably five; one for each voltage output) of regulators supplying each output voltage from the step-down intermediate supply. Use inverting switches for the negative; use whatever you feel comfortable with (LM7805, etc) for the + voltages (still somewhat expensive, and now you have to make it work).

Rusty Carruth
Tempe, AZ

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