OHMS LAW

VR2GY

OHMS LAW
This is what I consider thefirst and most fundamental lesson in electronics.
I sob every time a licensedelectrical contractor contacts me for help over some electronic device and hedoesn't know the basics. Do they sleep through the first semester?.
I will keep this dead simple. Iwon't introduce any complications. Everybody capable of reading will understandit and hopefully never, ever, ever forget it. I will not give highly technicaldefinitions to confuse the newcomer. There are four basic electrical unitshere. They are (1) Power  - in watts - [P],  (2) Voltage - in volts -[E],  (3) Current - in amperes or amps - [I] and  (4) Resistance - inohms - [R].  Now how basic can you get? Easy to remember!.

OSCILLATOR
An oscillator is an electroniccircuit where some of the amplified output is fed back to the input to maintaina flywheel effect or oscillations. Circuit design, components and layout thefrequency of oscillation. For extreme accuracy we might use a crystal tomaintain frequency.
At its most basic we coulddesign one simple oscillator circuit to operate at 7050 Khz. Although notrecommended we could apply and remove power at a morse code rate and we wouldhave a simple yet extremely crude C.W.transmitter operating in the 40mamateur radio band as a Q.R.P.transmitter. Don't even think about it!.

RECEIVER
A collection of circuitsdesigned to receive signals over one or more bands of interest and covering oneor more modes of operation.
At its most simplest it couldbe a crystal set designed to receive the a.m. radio band. At its most complexit could be a very sophisticated surveillance receiver designed to coveranything and everything.
Typical receivers are a.m. /f.m. tuners, t.v. receivers or s.w. radio.

RTTY or rtty
This stands for Radio Teletypewhere amateurs, amongst others, would transmit signals generated by a keyboarddevice not unlike you sending email. Instead of an internet connection you havea radio connection. I had only a passing interest in this aspect of the hobbyand that was about 25 years ago. As to what is happening today I don't know butI suspect it's a fair bet that computers and packet radio (bit like the www)have overtaken it.

QRP or qrp ( Low Power Transmission )
This is a very much reducedpower mode of operation favoured by many amateur radio operators because of theskill and challenges involved in making contacts.
Power is limited to 5 wattsmaximum on C.W. or 10 watts on S.S.B. although of course often less is used.Because of the low power output the equipment can be battery operated and isquite suitable for portable operation.
Frequently Q.R.P. activitiesare conducted in conjunction with other recreational pursuits such as fishing,camping etc. Often the equipmentis home made (home brewed).
Personally I think it is thelast frontier in any hobby in a world that has gone mad with "buy thelatest-greatest-all singing-all dancing ready made gizmo's". It takes realtalent to be a classy Q.R.P. operator. Unfortunately I wouldn't count in thatcategory. "Those who can do! - those who can't teach!" <grin>
If you are looking for a realchallenge in one of the finest fraternities in the world then start right here.But first go and get a license.

S/N RATIO
Signal to Noise Ratio. Noise is the ultimate limiting factor in the reception of radio signals. Noiseis generally classified as either natural (QRN) or man made (QRM).
Natural noise emanates fromgalactic and atmospheric noise picked up by the antenna as well as thermalnoise generated in the antenna itself. Similarly man made noise such afluorescent lights, motors and a host of other appliances and tools is alsopicked up by the antenna. These sources of noise are then amplified by thevarious stages in a receiver. However these amplifying devices create noise oftheir own also.
The noise problem varies withthe frequency of reception. Generally the noise figure of a receiver (i.e.allowing for the noise generated by the receiver itself) is not of greatimportance for frequencies somewhat below 30 Mhz because the external noisecombined i.e. natural and man made will always exceed the noise figure of thereceiver.
Visualise if you can, anarbitrary noise level of 10 uV - these figures are for comparative orillustrative purposes only and bear no resemblance to reality. Now that is 10 onemillionths of a volt.
If we wished to receive acertain signal that was received on our antenna and had a strength of say 1000uV or 100 times the noise voltage you can see such a signal would be copiedquite readily. On the other hand if a desired signal was only 1 uV (and manyoften are at this level) then the noise level outweighs it by a ratio of 10:1.
Now that is a pretty roughexplanation but you should get the general idea. Of importance to reception,the narrower the bandwidth of the receiver, the bigger the improvement to yourprospects of recovering the desired signal.
Once a desired signal drops inlevel in comparison to noise in a particular location then all hope of recoveryis lost.
This is a highly technicaltopic which is almost a science in itself. I have attempted to do no more thangive you a general appreciation of the topic.

SSB or ssb ( Single Side Band )
Assuming you have read thesection on A.M.you would be aware that two of the disadvantages of a.m. transmission are thetwice the bandwidth to convey the same information and only 25% of the power isused in each side band. The remaining 50% of power is expended in the carrier.
It makes more sense in terms ofeconomy of bandwidth as well as economy of power to simply transmit only oneside band. This is called S.S.B. or Single Side band.
If our carrier (initially) inthe transmitter is say 9000 Khz or 9 Mhz and we modulate that signal withuseful voice frequencies of say 300 Hz to 2400 Hz (this spectrum contains alluseful information and indeed is roughly the bandwidth of your telephonesystem) then dealing with the highest frequency of 2400 Hz (2.4 Khz) we getside bands (including carrier) of 000 Khz to 9002.4 Khz as well as 9000 Khzdown to 8997.6 Khz.
Fifty per cent of our power isin the 9000 Khz carrier and 25% in each of our side bands. At high power levelsthis would be both wasteful and inefficient. In fact at this point in ourtransmitter we are only dealing with very low power levels.
What if we introduce a highlyspecialized and highly accurate filter that will only accept frequencies in therange of 9000.3 Khz to 9002.4 Khz and reject all others. Presto we have asignal which occupies a bandwidth of only 2.1 Khz wide, therefore more channelsthen can be accommodated in the same band. Further the power amplificationformerly available to us can now be devoted exclusively to our narrow band signalin a linear amplifier.
Unfortunately at the receivingend things get a lot more complicated and expensive. Firstly our I.F. Amplifiermust accept signals no wider than the 2.1 Khz. In practice you use a similarcrystal filter or if the receiver is part of a transceiver then you use thesame filter as was used in the transmit section. Secondly because no carrier istransmitted with the S.S.B. signal we must provide one locally in the receiver.This is called a B.F.O. or Beat Frequency Oscillator and 9000 Khz is typicalbut not the only frequency or method.
When mixed with the receivedsignal the B.F.O. and Detector (sometimes called Product Mixer) will put outour original audio of 300 Hz to 2400 Hz. All other frequencies are filteredout.
In the transmit section the9000.3 to 9002.4 signal is mixed with a local oscillator signal or frequency toproduce a signal at our final frequency of transmission.

SWR or swr
This is called Standing WaveRatio (or more correctly V.S.W.R.) and is much beloved by many who like tobecome paranoid over something. For some unknown reason C.B.'ers seem to excelat this.
Contrary to popular belief itis not the holy grail. Whilst everyone should strive for technical excellenceas well as efficiency there is absolutely no reason to slash your wrists becauseyou can't get an ideal S.W.R.
In fact I can personally 100%guarantee that the sky will not fall in on you. What is acceptable depends onmany things including your site, set up and circumstances. Efforts and expenseto achieve a perfect S.W.R. are frequently all totally out of proportion.
A transmitter requires a loadto deliver power to. This is called an Antenna.
If some of the transmittedpower is reflected back along the transmission line toward the transmitter thenwe have a situation where voltage standing wave patterns exist.
"The ratio of the maximumvoltage on the line to the minimum value (provided the line is longer than aquarter wavelength) is defined as the voltage standing wave ratio orvwsr"
It is often mistakenly assumedthat power reflected from a load is power lost. If there is proper matching atthe input end of the line this is only true if there is considerable loss inthe line itself.
Be technically efficient notparanoid.

S METER
I assume you understand both I.F.amplifiers and automaticgain control (A.G.C.)
An S-meter is simply a meterset up to measure the current through the agc control line so that on strongsignals it shows say S9 + 20 dB while on weak signals it might be at the bottomend of the scale on say S1 or S2.
Be aware, S-meters arenotoriously inaccurate, can not be compared between various receivers and areonly useful for relative measurements applicable to your receiver, using yourcurrent antenna, at your present location and on one particular band. They arewidely misunderstood and all too often given a level of importance they don'trightly deserve.
S-meters are as accurate as agroup of people standing by the road and individually estimating the speed ofpassing vehicles.

TRANSCEIVER
A unit which contains both thetransmitter and receiver. It has the advantage that common electronic circuitsare shared rather than duplicated if you operated the two units separately.

TRANSISTOR
Firstly we had valves and thentwo bright sparks in Bell Labs. back in 1948 invented the transistor. Almostsimilar to a valve (triode) the transistor has revolutionized the world.
Not only are there types whichhandle very high voltages there are types capable of very large amounts ofpower. Because of transistors much equipment has shrunk to a fraction of itsformer size while extending capabilities almost beyond imagination.
By the 1960's transistors beganto become integrated together in single packages to perform all sorts of logicblocks. The digital explosion had begun.
Today literally millions andmillions of transistors are formed on the one thin wafer to produce deviceslike the Pentium III processor at previously unheard of speeds and power.
I guess the only limit is man's/ woman's imagination.

TRANSMITTER
see Oscillator

UHF or uhf
300 Mhz to 3 Ghz (that's 3,000Mhz or 3,000,000,000 cycles per second) - this band is occupied by U.H.F. T.V.,some radar installations, mobile phones, two way radios and a heap of otherexciting stuff.

USB or usb ( Upper Side Band )
Identical but the directopposite to L.S.B.(Lower Side band) - see also A.M.and S.S.B.

VHF or vhf
30 Mhz to 300 Mhz occupied bytraditional T.V. stations, some amateur bands, commercial two way radio,maritime and aircraft bands as well as the F.M. radio band of 88 - 108 Mhz.

WAVELENGTH
Originally in radio, thefrequency of signals was not mentioned. The custom was to refer to the 'wavelength'.
This is easily computed from:

300,000,000 / Frequency (cycles)  or  300 / Frequency (Mhz)

In reality this indicates, froma purely technical standpoint, that a wavelength is determined by dividing thespeed of light by the signal frequency in cycles per second. The underlyingreason here is that radio waves do travel at the speed of light. This isapproximated as 300 million metres-per-second (and no correspondence will beentered into on that point).
Just how the custom of talkingin wavelength originated I have never been able to establish. I suspect it hada lot to do with transmitting antennas where the calculation is quite critical.
As frequencies increased byabout the 1930's the wavelengths diminished in physical size to the point theterm 'short-wave' came into vogue.
To understand radio waves etc.visualise a pebble dropped into a pond. At the point where the pebble hits thewater the transmitting antenna is situated. Waves then radiate outward fromthat antenna.