AREDN Mesh Node

My portable node includes these major components:

1. Microtik hAP AC with power transformer from Isaac
2. Ubiquiti Nanostation M5 from Isaac
3. Cisco SPA525G VoIP (Voice over IP) phone from Isaac
4. Sercomm V-RC8061 PT IP camera from Marni

Minor and ancillary components:

1. Powerpole splitter (at least 3-port)
2. USB car charger (at least 2-port)
3. Homemade 12VDC power cable (barrel connector for Microtik to powerpole)
4. Homemade 12VDC power cable (car accessory female socket to powerpole)
5. 2x homemade 5VDC power cables (barrel connector for phone and camera to USB)
6. Bioenno 3Ah LiFePO4 12VDC battery with powerpole connectors (may switch to sealed lead acid or higher capacity)
7. Windows computer with USB NIC (network interface card) to give it an Ethernet port
8. 2 Ethernet cables (Cat 5e, I think)
9. Cheap 60" camera tripod ($20 used on eBay, equal to $40 new from BestBuy: https://www.bestbuy.com/site/dynex-60-universal-tripod-silver/8241048.p?skuId=8241048)
10. Cell phone
11. Ziplock bags, zippered bag with handle, and 3 large reusable zip-ties

Major steps included:

1. Flash firmware to hAP: https://www.arednmesh.org/content/installation-instructions-mikrotik-devices
2. Configure hAP
1. Name: KJ6LDJ-HAP
2. Mesh RF disabled
3. Tx power 22 dBm, distance to farthest neighbor 35 km
4. LAN Mode 5 host Direct, DCHP server checked
5. LAN Access Point enabled; AP band 2GHz; SSID: sfwem; password: standard sfwem password
6. WAN Wifi Client configured to home network for tunnel while home
3. Enable PoE passthrough on hAP (in Setup, Advanced Configuration)
4. Flash firmware to NSM5 (Isaac did this part)
5. Configure NSM5
1. Name: KJ6LDJ-InnerRichmond-SECTOR
2. Mesh RF enabled with IP 10.106.70.188, netmask 255.0.0.0, SSID AREDN (-10-v3 automatically appended), channel 179 (5895), width 10 MHz
3. Tx power 27 dBm, auto distance
4. LAN Mode 5 host Direct, DHCP server checked
5. WAN protocol DHCP, DNS's 8.8.8.8, 8.8.4.4, both advanced WAN access options unchecked
6. Attach everything to the tripod
7. Connect battery to hAP to NSM5
8. Set up tripod and aim NSM5 roughly at where existing nodes are located
9. Connect phone over wifi to hAP's "sfwem" network configured in 2.e, above
10. Open phone's browser to kj6ldj-hap.local.mesh:8080
11. Open Charts, enable Sound, aim for max SNR, then click "Quit"
12. Mesh Status, open various Services hosted but other nodes, and use them!

Next iteration may be to take aspects from Jeffrey KI6SGV's setup: https://github.com/italic-r/AREDN-PAN

Action shot of my first connection, from the Presidio Golf Course:

Math of Transformers

Purpose: To understand briefly the math of the forces at work in a transformer, especially an impedance transformer for RF antenna systems.

Scope: AC circuits only, including 50 Hz power, 5 GHz microwave, and everything in between.

Math:

Ohm's law:

    V = I R

    I = V / R

Generalized to complex domain (for alternating currents with reactance) becomes:

    V̇ = Z İ ₍₁₎

    İ =  V̇ / Z ₍₁₎

Faraday's law: A changing magnetic field (ΔΦ/Δt) induces a voltage (Emf = V), and a changing voltage induces a magnetic field based on the number of turns on the ferrite core (N):

    V = -N ΔΦ / Δt (2)

Electrical power:

    P = I V

Combined with Ohm's law:

    P = V² / Z

The magnetic field induced on the ferrite core by the input in turn induces a voltage on the output (see caveats):

    ΔΦ1 /Δt = ΔΦ2 / Δt

Insert Faraday's law:

    -V1 / N1 = -V2 / N2

    V2 =  (N2 / N1) * V1   <-- This is the critical equation for a voltage transformer

Because energy is conserved and transformers are (by design) efficient (with efficiency η):

    η P1 = P2

Insert Ohms law:

    η V1² / Z1 = V2² / Z2

And if you substitute the voltage transformer equation:

    η V1² / Z1 = ((N2 / N1) * V1)² / Z2

    η V1² / Z1 = (N2 / N1)² * V1² / Z2

    η / Z1 = (N2 / N1)² / Z2

    Z2 = (N2 / N1)² * Z1 / η   <-- This is the critical equation for an impedance transformer

Both voltage and impedance transformations occur, but usually only one equation is important for the specific application.

Caveats: Saturation and efficiency of the toroid core are dependent on its size and chemistry and the frequency and amplitude (power) of the driving signal. Saturation is when f1 no longer equals f2.

Example 1: A perfectly efficient (η=1) transformer with 3 primary windings (N1) and 21 secondary windings (N2) has an output voltage that is 7 times the input voltage and an output impedance 49 times the input impedance. If the desired output impedance is 50Ω, the target input impedance is 2450Ω.

Example 2: If the transformer is 95% efficient (η=0.95) with the same setup as Example 1 and an input impedance of 2450Ω, the resulting output impedance will be 52.6Ω.