Building The Net

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) / (4Ï€))

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

Fun with FLDigi and Contesting!

This was a fun video to do. With all the waiting for replies it can get a little boring.

This video is a good reference, but I need to do another step by step due to changes in N1MM+

I did this video using a new tool to capture screen activity. I think the quality is much better then the previous method I was using. Let me know your thoughts!

This video show how to setup FLDigi to use your internal sound card as the coder / decoder for Amateur Radio Digital Modes.

Tossed this together as part of a series on digital modes for Amateur Radio. This is the first installment and covers installation of FLDigi, the premier open source software for Amateur Radio digital modes.

Is contesting really important to the hobby?

That question comes up a lot when talking to new hams. Although discussed in some detail in the ARRL Technician’s Handbook, the actual Technician test (at the time of this writing) has very few questions that mention contesting. Many General and Extra class operators don’t seem to get ‘the whole contest thing’ as well.

So why are contests important? Why should we care about radio sport at all? And what does this have to do with the new proposal put forward by ARRL to the FCC to grant additional HF privileges to Technicians?

Read more »