Building The Net

How Much Voltage Drop Should We Plan For With 12V DC Power Systems?

Guide to your First HF Rig.

An interview with the folks that lead the planning for the Ventura County wide 2020 Field Day.

— Stu AG6AG

— Stu (AG6AG)

Every time I have to figure out ERP or dB gain I always have to search the Internet to find the formulas. Well, I figured I could just look them up here if I posted them, so here they are!

Calculate dB gain based on actual output change. This is good for working out how much gain and amplifier gives you:

10 X log(power/refpower) = dBm Gain / loss

Example using 65 Watt output from radio into an amp and seeing that the output power is 500 Watts.

10 X log(500/65) = 8.86 dBm gain

Calculate dBm from output power:

10 X log(1000 X output watts) = Total DB Output

Example using a 100 Watt output.

10 X log(1000 X 100) = 50 dBm Output

Calculate output power from dBm

10^(dBm/ 10) / 1000

Calculate ERP based on radio output and Antenna gain:

Radio Power * 10^(dBm gain/10) = ERP

Example using 100 Watts radio output and a dB gain of 9 dBm from the antenna system:

100 * 10^(9/10) = 794 Watts

Calculate percentage of gain or loss based on dB

1 - (10^((-(dBm Loss/10)))) = Percentage of Loss

10^(dBm Gain/10) = Percentage of Gain

Example using a 3 dBm loss and gain:

Loss:
1 - (10^((-(3/10)))) = 50%

Gain:
10^(3/10) = 200%

Calculate SWR Power Loss Percentage:
(SWR -1 )² / (SWR + 1)² = Percentage of Loss

Power and Attenuation Calculations:
(all voltages are RMS)

Drop in dBm = 20 x log(R1 / R2)
Example: 50dBm = 20 x log(8000 / 25)

R1 = 10^(dBm / 20) x R2
V = √(Watts x 50Ω)
Watts = V² / 50Ω
Watts Required = V² / R1

Bulletin 65 Formulas:

Power Density:
S = PG / 4πR²
Where:
S = power density as mW/cm2
P = power at input of antenna
G = power gain of antenna in the direction of interest
R = distance to the center of the radiation of antenna

Max Power for Distance:
Max Power Density X (4π X (Distance²) = Max Power

Minimum Distance:
Square Of((Power / Max PD) / (4π))

Adding for Reflection:
ERP X (1.6)²

There are the two I use all the time. These two also serve as a really good platform for all sorts of calculations. One note, if you are looking for Voltage Gain, change the base 10 to base 20.

— Stu

A lot of work went into this video… I hope it answers some questions.

This is useful for those that are involved in EMCOMM for their local Civil Defense Group.

This was fun… Got a QSO with a KH station as well!

Fun with FLDigi and Contesting!

Turning additional color codes on in WSJT-x really make a difference.