DECIBELS:

The decibel is not a measure of a particular electrical unit and therefore figures that are expressed as a decibel are completely meaningless unless they are related to a particular reference. A decibel is actually one tenth of a Bel and is derived from the logarithmic ratio of two voltages or current or power levels: One of these levels must be measured to act as the reference point in order that the other level (or levels) can be expressed as dB relative to that point.

So; Decibels (dBs) represent a RATIO of one voltage to another, or one power to another at the same impedance. Decibels can be either a positive figure representing gain or a negative figure representing a loss.

Here is a table of decibel relationships:

dBs are added to represent the total gain or the total loss, while the gain or losses that are expressed as fractions must be multiplied.

e.g. a power gain of 2.5 dB is dealt with thus: 2.0 dB plus 0.5 dB i.e. 1.585 X 1.122 =  1.778


Examples:

+ 3dB  =  2 x the power (or twice the loss, for example when dealing with feeder losses) or 1.4 times the voltage
+ 6dB  =  4 x the power or 2 x the voltage or approximately 1 "S" point
+ 9dB  =  8 x the power or 3 x the voltage
+10dB = 10 x the power or 3.16 x the voltage or approximately 1.5 "S" points
+20dB = 100 x the power or 10 x the voltage or approximately 6 "S" points

Transmitter Power

Transmitter power is often expressed in Watts, but in amateur radio it is common to find transmitter power expressed in dBW. This is the power in decibels relative to one Watt.

e.g. if a transmitter is quoted as having an output of 6dBW then that would be the same as saying that the power is 4 watts. If a transmitter is quoted as having a power of 14 dBW the 10dBW figure (i.e. 10 watts) is multiplied by the 4dBW figure (i.e. 2.5 watts):  10W x 2.5 =  25 Watts.

Here is a table showing the conversion between dBW and Watts:

COAXIAL & OTHER FEEDER CABLE LOSSES COMPARED

When using an antenna at its resonant frequency  the VSWR should be very low and losses at HF should also be very small. However when it is anticipated that an HF antenna will be used for wideband, non resonant, operation (e.g. a popular all band 'Doublet') the VSWR could be significantly higher and losses in coaxial cable will be higher  than with a resonant aerial.

e.g. at 28 MHz when using an antenna with an SWR of 9:1 it may be perfectly possible to match the antenna system to the transmitter using an Antenna Matching Unit ("ATU"), but if using a 20 meter length of RG58 coaxial cable the losses could be around 3 dB - in which case 100 watts of transmitter power would only result at 50 watts reaching the antenna terminals.

Alternatively if Twin Feeder is used to feed an antenna such as an All Band Doublet where high VSWR will be expected the loss at an SWR of 9:1 would only be about 0.3 dB which would equate to over 90 watts reaching the antenna terminals!

	With an SWR of 1:1 at antenna  Losses in dB per 100 meters at various frequencies Cable Type: 3.5 MHz 10 MHz 30 MHz 50 MHz 144 MHz 432 MHz RG58 2.5 4.3 7.7 10 17 32 RG8 Mini / RG8-X 1.7 2.9 5.4 7.1 13.2 26.5 RG8 1.06 1.8 3.2 4.2 7.6 9.1 RG213 1.1 2.0 3.5 4.7 8.4 15 Westflex 103 0.6 0.9 1.7 2.7 4.5 7.5 450 Ohm Twin 0.17 0.29 0.51 0.67
	With an SWR of 3:1 at the antenna  Losses in dB per 100 meters at various frequencies Cable Type: 3.5 MHz 10 MHz 30 MHz 50 MHz 144 MHz 432 MHz RG58 3.4 5.5 8.9 11.3 19.1 34.3 RG8 Mini / RG8-X 2.4 3.9 6.6 8.4 14.5 27.7 RG8 1.6 2.6 4.2 5.4 8.8 15.7 RG213 1.7 2.8 4.6 5.8 9.7 17 Westflex 103* 1 1.5 2.5 3 5 9 450 Ohm Twin 0.28 0.47 0.8 1.03
	With an SWR of 6:1 at antenna Losses in dB per 100 meters at various frequencies Cable Type: 3.5 MHz 10 MHz 30 MHz 50 MHz 144 MHz 432 MHz RG58 4.9 7.1 10.7 13.1 20.9 36.1 RG8 Mini / RG8-X 3.7 5.5 8.3 10.1 16.4 29.5 RG8 2.5 3.8 5.8 7 10.7 17.5 RG213 2.8 4.2 6.3 7.6 11.5 19 Westflex 103* 1.6 2.2 3.2 4 6 10 450 Ohm Twin 0.49 0.82 1.37 1.73
	With an SWR of 9:1 at the antenna Losses in dB per 100 meters at various frequencies Cable Type: 3.5 MHz 10 MHz 30 MHz 50 MHz 144 MHz 432 MHz RG58 6 8.4 12.1 14.5 22 37.5 RG8 Mini / RG8-X 4.7 6.6 9.6 11.5 17.1 30.1 RG8 3.3 4.9 7 8.3 11.9 18.9 RG213 3.6 5.2 7.5 8.8 12.8 20.4 Westflex 103* 2 2.6 3.8 4.5 6.5 10.5 450 Ohm Twin 0.71 1.16 1.88 2.34

Losses are given a dB per 100 meters. For other lengths divide dB loss figure by 100 and multiply by the actual length in meters.

These loss figures are for the cable only without connectors and do not take into account termination and other losses.

References:

http://www.ocarc.ca/coax.htm

http://www.timesmicrowave.com/cgi-bin/calculate.pl

http://www.kc7hxc.us

http://whwestlake.110mb.com/

RG58 CQ125; RG8X Belden 9258; RG8 Belden 8237; RG213 Belden 8267
* Westflex103 unconfirmed estimated loss at higher SWR's

RESISTOR COLOUR CODE CHART & CAPACITOR INFORMATION

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CALLING CQ and other RADIO ETIQUETTE
(Adapted from HamSphere)

Calling CQ:

e.g. your call sign is CD456

1. Find a clear frequency. If not sure whether the frequency is clear, ask before proceeding.

2.Call "CQ CQ CQ. This is Charlie Delta Four Five Six calling CQ CQ CQ.  Charlie Delta Four Five Six, CD456 calling CQ and waiting for any call."

Listen for any return call.

3. You hear "Charlie Delta Four Five Six this is Echo Foxtrot Seven Eight Nine, EF789 calling."

4. You respond by saying "Echo Foxtrot Seven Eight Nine this is Charlie Delta Four Five Six.  Thank you for the call your signal is 59 (give accurate signal report using the RST system). My name is [your name] and my QTH is [your location]. How do you copy my signals? EF789 this is CD456 over."

5. Engage in conversation about other topics (location, weather, type of radio and antenna etc) - Find ways to get to know each other rather than simply exchanging signal reports and 73s!

6. End an HF contact by giving both call signs and signing off. For example: "... thank you Jim for the contact and 73 to you and your family.  EF789 this is CD456 signing off and clear."


Amateur radio etiquette:

* Do not transmit before first checking that the frequency is clear.

* If more than one station responds to your call and you can hear one call clearly then simply respond to that station as described.

* If only parts of the call sign is heard (e.g Foxtrot Whiskey or what ever) then in step it may be wise to respond by saying
"the station with the Foxtrot Whiskey call sign please make your call." When the complete call sign is established the QSO can continue.

* Be polite at all times rand promote friendship.  If not, avoid transmitting.

* Set a good example especially for short wave listeners who may be thinking about becoming an amateur.

* Be a good listener- make some brief nots to keep track of topics / subjects etc.

* Always reply to CQ calls if possible, and call CQ yourself.  It helps keeps amateur radio alive.

* Speak clearly and slowly, especially when giving your call sign to someone you have never worked before.

* Try to keep track of everyone in the QSO.  Hopefully someone has assumed the role of "traffic director" to make sure everyone has a chance to contribute to the discussion.  If not, don't hesitate to do it yourself.

* Make it clear at the end of each transmission which station is expected to transmit next.

* Operate on frequencies that are in whole KHz (e.g. 14.325 Khz). This alleviates ambiguity and makes it easier for everyone to be on the same frequency.

* Allow  enough separation between between your transmission and other transmissions so as not to cause adjacent channel interf