1. 2 dB or not 2 dB: That is the question (again)
Karl Moellmer, W7BVP
12-Jan-2019

2. 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?

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

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

5. 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

6. Filter Band Width (3 dB):

7. Antenna Beam Width (3dB):

8. Some other dB terms
dBm, dBi, dBd & dBc

9. 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

10. 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)

11. 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)

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

13. Losses between your transmitter and his receiver….

14. 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

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

16. 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.

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

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

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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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