2 dB or not 2 dB: That is the question (again) Karl Moellmer, W7BVP 12-Jan-2019

POWER GAIN AND POWER LOSS Decibel Wrap-up SWR: Live with it or fix it? Why didn’t he give me an S-9 report?

Logarithms 104 = 10,000 (Look….4 zeros) •Log 10,000 = 4

dB = 10 Log (P1/P2) 10 x log of a power ratio …Decibel REVIEW… dB = 10 Log (P1/P2) 10 x log of a power ratio

Decibel TRICKS 3 dB: 10 dB: Double the Power: 10 Log (2/1) = add 3 dB Half the power: 10 Log (1/2) = subtract 3 dB 10 dB: Up the power by 10 times: 10 Log (10/1) = add 10 dB Drop the power by 10 times: 10 Log (1/10) = subtract 10 dB

Filter Band Width (3 dB):

Antenna Beam Width (3dB):

Some other dB terms dBm, dBi, dBd & dBc

dBm = 10 Log (P/1 milliwatt) Jim Creek used to run 1 Million Watts How many dBm? dBm = 10 Log (106/10-3) = 90 dBm

Antenna items: dBi = 10 Log (antenna main lobe power/ theoretical isotropic antenna power) dBd = 10 Log (antenna main lobe power/ theoretical dipole antenna main lobe power)

So if you’re an antenna salesman, are you going to advertise your antenna gain in dBi or dBd? dBi! It’s 2.15 greater number than dBd (More impressive)

dBC: The number of decibels a harmonic or spur is below its fundamental

Losses between your transmitter and his receiver….

Consequence of high SWR in your antenna feed line Do you REALLY need to fix it? How to fix it? A Balun? (Balanced to Unbalanced) (A transformer) AND…Cut the antenna for resonance at your desired frequency

Consequence of high SWR into your transmitter final amplifier How to fix it?

R, S, T reports R: Signal Readability 1 – Unreadable……..5 – Perfectly readable S: Signal Strength 1 – Faint signal, barely perceptible……9 – Extremely strong signal What is “50 over 9”? T: Signal Tone (Used with CW) 1 – 60 Hz or lower, very rough…….9 – Perfect tone.

Why DIDN’T THAT GUY GIVE ME AN S-9 Report?

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver He had high loss feed line

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver He had high loss feed line He had a poor antenna

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver He had high loss feed line He had a poor antenna He was in Antarctica

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver He had high loss feed line He had a poor antenna He was in Antarctica Bands were bad

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver He had high loss feed line He had a poor antenna He was in Antarctica Bands were bad My antenna is poor

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver He had high loss feed line He had a poor antenna He was in Antarctica Bands were bad My antenna is poor My have high loss feed line

Why DIDN’T THAT GUY GIVE ME AN S-9 Report? He had a crummy receiver He had high loss feed line He had a poor antenna He was in Antarctica Bands were bad My antenna is poor My have high loss feed line I am running low power