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Tech Forum Questions

Thermostat Schematic June 2012

I need a simple schematic diagram which shows how the home thermostat controller is connected to the gas heater and to the air conditioning at the same time.

via email


Here is documentation for a typical thermostat. Make sure you know what voltage your existing system uses before making a purchase.

I think the schematic is self-explanatory

Larry Kraemer
via email

Generator Conversion June 2012

I’m considering converting an old car with manual steering to electric. However, DC motors about 10 HP or more are expensive. I saw that the Northern Tool catalog has a 10 kw generator head with brushless technology (Item 165928). Is this a 13 HP brushless DC motor I could modify?

Peter Vickers
Hope Hull, AL


You can ask the expert at Northern Tool, but I am sure he will tell you that this is a single phase, 220 VAC generator and cannot be used as a motor. A three-phase generator could possibly be used as a motor, but 60 Hz machines don't like to be run at other frequencies so variable speed would be a problem. You would need a clutch and transmission.

Russ Kincaid
Milford, NH

Compressor Starter June 2012

I am looking for a positive temperature coefficient motor starter for a compressor. Or, I need help using different parts such as a single pole contactor/relay for a hard start. The part I want to replace has the following number: RF-6850-18, and consists of a PTC starter and an overload protector. Can I replace this with a hard starter contacter? I can photocopy the schematics and email anyone who can help me.

Michael Farley
Cincinnati, OH


The original part is shown at www.repairclinic.com/PartDetail/Start-Device/RF685018/1569121.

The three terminals on the device are C, S, and R. C is connected to the COMMON of the compressor, with S being START winding, and R being RUN winding.

I'd suggest replacing the original device, and adding the proper MARS hard start device to kick the compressor. You don't want to bypass the overload! PERIOD!

MARS Motors & Armatures, Inc.,  has hard start devices and torque multipliers for refrigeration/AC compressors. I've used a smaller MARS hard start device on several refrigerators, and they work fine. (www.marsm-a.com/CGI-BIN/LANSAWEB?WEBEVENT+R06630136135017015394091+ML6+ENG).

I can't find the paperwork on the last MARS device I purchased. Any local HVAC distributor should be able to locate what you need, depending on the compressor size. It's just a two wire hookup.

I'm including a PDF document from MARS and my refrigeration document for you to view.

Larry Kraemer
via email

I work for a major appliance repair company/retailer. Replacing the factory compressor start device with an after-market hard start kit is not recommended. Most of those kits — if not used or sized correctly — can cause permanent compressor failure. I would suggest trying to source the correct part by model and serial number of the refrigerator. There is a major appliance parts dealer in Cincinnati and Dayton that can help. If you can not find a model or serial, I suggest Whirlpool part number 8201786. This kit covers several different compressors, as well as wiring connections.

Sean Battito
Mohnton, PA

I've bought PTC starters for refrigeration compressors from www.repairclinic.com on a few different occasions. A local appliance shop with a parts counter should be able to supply them too, either OEM or a universal replacement. The "hard start" kits you can get are nothing more than a standard PTC starter, overload protector, and capacitor stuffed into a housing. The one time I tried one of those, it failed within a few weeks.

If you want to try rolling your own, this schematic is said to work although I've not personally tried it. Digi-Key, Mouser, and other electronics distributors carry a selection of PTCs and bimetal circuit protectors that could be used.

James Sweet
via email

Go to any well stocked refrigeration supply house and ask for a universal compressor starter.

This will be a device with leads. (I have no idea what's inside.) Connect it as shown on the package, removing the existing starter device.

These things work every time. Be sure to leave any original thermal protective device intact.

They can also be used on small air compressors that use PTC devices as starters.

Don Pomeroy
Manchester, NH

Digital Technology? June 2012

I am a senior citizen plagued with hearing loss. I have been using hearing aids for about 30 years!! The vendors keep touting "digital" technology although none of them can explain how "digital" amplifiers work. I am familiar with analog amplifiers. Can someone give an explanation of this "digital" technology?

William Porter
Porter, OK


An advanced digital hearing aid employs digital signal processing for all sorts of tricks. For one, the individual's hearing loss spectrum can be compensated without large analog filters. But DSP also allows for the removal of noise, constant tones (real ones), feedback, etc. and for the adjustment of gain and directionality. I think I've read that certain types of tinnitus can be reduced by sufficient levels of band-limited noise. Apparently, the brain interprets zero noise as a tone. Such noise generation is easy with DSP.

Charles Wenzel
Austin, TX

Analog amplifiers amplify all audio frequencies equally, simply making everything louder. Digital hearing aids process the digitized sound with a tiny microprocessor before converting the digital signals back to analog for your ear. Therefore, they can be programmed to amplify different frequencies by different amounts.


Most senior citizens with hearing loss have more loss of high frequencies than low.  Unfortunately, it's the high frequencies that convey most of the meaning of speech. Your audiologist will probably program your digital hearing aid to amplify high frequencies more than low, resulting in much better speech understanding than simply making everything louder.


It usually takes two or three trips to the audiologist to get your hearing aid programmed just right for you. That personal attention is built into the price of the digital hearing aid, which is why they're so expensive. Believe me, they're worth the extra cost!

John Herro
CIncinnati, OH

A digital hearing aid still has an analog microphone, mic pre-amp, audio power amp and speaker (earpiece). It's what's in the middle that's digital: a programmable digital signal processor. The DSP takes the mic input and converts it to bits of data (digital). The DSP can analyze the data and make adjustments depending on the programming. For example, if you have a hearing loss at 2,000 Hz the audiologist can program a boost in your hearing aid at 2,000 Hz. If after some time your hearing becomes diminished overall, the audiologist can program a general boost of all the frequencies if needed. The DSP can make smart decisions to automatically reduce or eliminate feedback and background noise. The latter can help you understand conversations in a noisy room. The DSP can automatically adjust the volume too. After the DSP does all this processing, it converts the bits of data back to analog and sends it to the audio amp. The beauty of a digital hearing aid is that a single design can be programmed to be used by many people without changing the electronics. All you need to have customized is the ear mold to fit your ear. An audiologist connects the hearing aid to a laptop computer to program its many parameters. Take a look at www.hearsource.com to see an example of how you can program your own digital hearing aid. As always, don't underestimate the value provided by your audiologist. Consider self- programming as fine-tuning and let the audiologist determine your baseline. (I am not a hearing professional. Consult with your doctor and audiologist for expert advice.)

Rick Swenton
Bristol, CT

I have been wearing "digital" hearing aids for three years. Here's what I've learned.

The "analog" aids of yesteryear were nothing more than sound amplifiers. Some could have been designed as high pass filters/amplifiers for those who lost high frequency hearing. Those analog aids also "squealed" at times from feedback due to the "microphone" (called pickup) hearing sound from the "speaker" (called receiver).

The "digital" hearing aids today operate using I.C. chips for DSP, Digital Signal Processing, and are tailored for each individual's specific type of hearing loss. This is done by "programming" each DSP chip for each ear based on results of a hearing test in order to overcome each ear's deficiency. The result is a custom made hearing amplifier for each of your ears.

The "digital" hearing aids also are programmed to avoid the feedback phenomenon, although they are not perfect. The "digital" hearing aids come in a variety of styles (behind-the-ear, in-the-ear, in-the-canal, etc) to suit the taste of the wearer. Prices vary all over the map with the best price I've found at Costco (Siemans hearing aids) for about $1200 apiece to as much as $5000 apiece at other hearing aid providers carrying a range of manufacturers.

None of these devices is "cheap" but they are effective depending upon one's specific type of hearing loss.

Curt Eglin
Shalimar, FL

Here's my brief explanation. Digital audio for a hearing aid can help in a number of ways. First it can (or should be able to be) tailored to your particular type of hearing loss. This means it should be able to amplify the frequencies you need help hearing and not amplify the frequencies you don't need help hearing.

It should also be able to reduce ambient noise, reduce feedback/screeching, and even more.

I found a good article at:


if you want to read more.

The bottom line is, if the people selling these things do not know the features of the new units, then go somewhere else because they need to be tailored to you. If they don't know that then it won't be done and there’s no advantage to buying it. Except for perhaps the reduction of noise and amplification of voice in general.

73 de ke3fl

Philip Karras
via email

VHF Receiver June 2012

Does anyone know of a VHF receiver that will tune in AM/SW signals after they've been frequency shifted up to the 216-302 MHz range? I would like to isolate the 500 kHz - 22 MHz band from a directional AM/SW antenna and use a local oscillator to raise them to 216-237.5 MHz. Then, I'd like to do the same for three other directional antennas to end up with four intermediate frequencies ranging from 216-302 MHz. I'm worried that a typical VHF tuner will only look for FM signals, of the wrong channel width, within the VHF band. These four new intermediate frequencies will now be high enough to make it through amplifiers (usually limited to 54-894 MHz) on our local cable system. I know that a local oscillator could be used at the receiver to bring them back down to their original range for use with a regular AM/SW radio, but I'm looking for an off-the-shelf solution without a hardware modified receiver. Can the "Uniden Home Patrol" or "GRC PSR-800" receivers have their Flash memory stored software modified to do this? The four separate intermediate frequencies will give the end user access to their choice of signals from four different directions. Something low cost, with an internal power supply (no wallwarts), and include Digital or SSB would be ideal. Thanks.

Sam Grauman
via email


My Realistic PRO 2004 allows the selection of AM detection at any time, and those receivers can be found on eBay for a pretty low price these days. You would be stuck with a fixed frequency step and no BFO, but that's probably fine for listening to foreign broadcasts. Another approach is a software-defined radio like the Funcube Dongle. That will require a computer, but it is really flexible and there's amazing free software, too. I'm surprised that you have that kind of directionality for such a wide frequency range; I would think that two antennas would be about as good as you can do.

Charles Wenzel
Austin, TX

A typical VHF receiver will only look for FM wide/narrow signals. At times I've noticed that even so, this type of receiver can sometimes "hear" an AM signal, not perfectly clear but understandable.

Better would be a wide-band or VHF/UHF "ALL-Mode" receiver that you can select the type of demodulation to use. My Alinco X10 is able to do what you're after. Can you borrow something like that? (There are so many on the new & used market!)

I checked eBay.com for "wideband receiver" and came up with a bunch from ~ $100 - $800 (Kenwood RZ-1 Wide Band Receiver) - (AOR AR-8600MK2/AR8?600MK2 Wide Band & ALL MODE Receiver/Scanner -unblocked- NEW)

Then there are the receivers in the thousands topped off with the new AOR AR5001D Wideband Receiver (DSP receiver) at $5,000.00

If you're going to bid/buy be careful! You need to make sure it can use any demodulation method, in your case AM/FMW/FMN at least, on any received frequency.

73 73 de ke3fl,

Philip Karras
via email

Your shortwave distribution via cable TV sounds most interesting!

I have reviewed the specs for the PSR-800 and Uniden Home Patrol receivers and find them to be less than ideal for your purpose.

1) The channel step size for these receivers is 6.25 kHz for the PSR-800 and 5 kHZ for the Uniden. Many longwave and shortwave stations are best resolved on 1 kHz or 9 kHz channel steps or smaller. Your listeners will not be able to tune in all stations.

2) The AM channel bandwidth for these types of receivers is in the order of 12 to 15 kHz which means that several stations may be heard at once.

Most shortwave receivers offer a 3 or 6 kHz filter bandwidth to better resolve shortwave stations.

A receiver such as the AOR8200 MK3 or one of its desktop equivalents, or one of the ICOM professional receivers such as the ICR-8500 (now obsolete) would be a suitable receiver and will permit CW, USB, and LSB reception.

You mentioned the use of a local oscillator as a down converter at the receiving end to facilitate use of a standard shortwave receiver. This would be an excellent option as you could use the frequency selector knob of the LO to directly steer your directional antenna selection (N,E,W,S) without having to retune the receiver. This would be functionally a superior method. Secondly, the use of a down converter frees the listener from having to calculate the LO offset used for each frequency and directional antenna.

The selection of shortwave receiver should be models which permit direct connection of an external antenna (the down converter output). In this way, interference from over the air signal to the cable provided signal can be minimized. There will be a delay, and resulting tone difference between signals leaking in from over the air and those of the cable system, so use of well shielded coax is recommended.

Something you should consider is that the TV channels on the cable system are generally adjusted so that their amplitude is equal on each channel to minimize reception of inter-modulation (IM - channel mixing) artifacts on television channels. Your shortwave channel will demand a larger dynamic range to receive weaker shortwave stations, so it is possible that IM products from the TV channels will be heard within the shortwave pass band. Likewise, the shortwave signals presented to the head end will have to be adjusted so that the aggregate power (in a 6 MHz channel bandwidth) does not exceed that of the channel power of the TV channels, or TV reception may be bothered.

You might also consider use of an FM modulated up converter and FM demodulator/down converter method where the 500 kHz to 22 MHz "base band" is directly applied to an FM modulator and recovered from a demodulator at the receiver. You may be able to find some suitable commercially available CATV FM video modulators and demodulators that will interface directly at the head end.

I experimented with this technique over an FM microwave link and it worked well, and because the base band is faithfully demodulated, there was no frequency translation error in the recovered signal.

Good luck on this project. I would be interested in hearing how it works out.

Joe Leikhim
Oviedo, FL

Solar LED Illumination June 2012

For several years, we have used a solar yellow LED deck lamp as a "Welcome Light" for our camper — the 12V "patio light" is just too bright, and ruins the moment. I would like to have a simple NiMH/NiCad amber LED light that would be charged via solar, but also from the 12V onboard power when available. I also need an on/off switch for the LED.

# 6121
William Hogan
West Lafayette, IN

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