Build a Central N3FJP Field Day Log Server With Local DHCP and GPS Time

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Centralized Field Day logging is one of those things that looks simple until the network hiccups, the generator burps, Windows decides it is “helping,” or one laptop thinks it is 2019 and another thinks it is next Tuesday.

My club was looking for an easy-to-use solution for FD 2026 that would tie all the logging computers in our main tent together to simplify log submission and track our total progress during the event. But past attempts with a logging server brought to light many issues, especially individual station computers locking up when there were server or network issues.

The goal is simple: all operators log to one reliable N3FJP server with consistent local IPs and accurate time without internet access.

Here is a practical way to build a central N3FJP Field Day logging server that does not depend on the internet:

One Windows server laptop or mini-PC that runs the N3FJP master FD log.

The server also hands out local IP addresses using a local DHCP Server for Windows.

All Field Day laptops connect to the same local wired LAN. Wifi should be avoided at all costs.

The server clock is synced via a GPS receiver using GPSTime.

A UPS that keeps the server and network gear stable through any power bumps.


Why build it this way?

N3FJP supports networking multiple PCs to a common log. N3FJP’s own networking help says Field Day is the “ultimate test” of a network and describes two approaches either traditional file sharing or TCP networking. TCP was added as an option to help groups that had problems with file sharing over slow or intermittent networks.

For a Field Day site, we decided to keep our equipment complement simple with one dedicated computer running N3FJP in TCP mode, a GPS dongle for time and software to hand out IP addresses to individual computers at each band station. Our network would use an Ethernet switch and did not need a router that might complicate setup and troubleshooting issues.

That avoids several common problems:

No dependency on internet time.

No mystery IP address issues.

No Windows file-sharing headaches.

Easier client setup: connect to Ethernet, open N3FJP and point to the server IP.


Parts list

Windows laptop or mini PC for the N3FJP server.

N3FJP Field Day Contest Log installed.

Ethernet switch.

Free DHCP Server software for Windows.

GPS receiver with NMEA serial output.

Free GPSTime program.

Small UPS for the server and switch.


Suggested Field Day LAN plan

Pick a simple private network and stick with it.

Example:

Field Day LAN:     192.168.73.0/24

Server IP:         192.168.73.10

DHCP range:        192.168.73.100 - 192.168.73.199

Subnet mask:       255.255.255.0

Gateway:           blank or 192.168.73.10

DNS:               blank

N3FJP server name: FD-SERVER

The LAN is completely internet independent. The logging clients only need to reach the N3FJP server.


Step 1: Prepare the server PC

Step 1: Prepare the server PC

Start with a dedicated machine that will be the “brain” of the logging network.

Install Windows updates.

Install N3FJP Field Day Contest Log.

Disable sleep and hibernation.

Important – Do these steps in this order since you will need to take the PC off the internet once you set the IP to static and set up the DHCP server.

Startup N3FJP and download Super Check Partial (if desired)

Download DHCP Server for Windows from dhcpserver.de (https://www.dhcpserver.de/cms/).

Set the server Ethernet adapter to a static IP (Settings>Network>Ethernet>Change Adapter Settings).






Select the Ethernet adapter, Properties, double click - Internet Protocol Version 4 and then fill in your IP address and subnet mask and select OK.

Example static server IP:

IP address:    192.168.73.10

Subnet mask:   255.255.255.0

Gateway:       leave blank

DNS:           leave blank





Name the computer something obvious, such as "FD-Log-Server" (Settings>System>About).

Step 2: Create the N3FJP Field Day log on the server

On the server:

Open N3FJP Field Day Contest Log.

Create a new Field Day log.

Save it in a known folder, for example:

C:\FieldDay2026\Club_Call-FD-2026\


Configure your Field Day class, section, call sign, operators and exchange.

Then log a test QSO.

N3FJP’s Field Day tips say the common log file should be placed somewhere accessible to the other PCs when using file sharing, and that clients should point to the correct log file. For this build, we are using TCP mode instead, but the same “know where your master log lives” still matters since you'll need to download the log later to submit it on the ARRL site.



Step 3: Install DHCP Server for Windows

Next we want the Field Day LAN to hand out local IP addresses automatically.

Install DHCP Server for Windows from dhcpserver.de (https://www.dhcpserver.de/cms/).

The project describes DHCP Server for Windows as a portable application that can run on Windows versions from Windows 95 through Windows 11.

Extract it somewhere simple, such as:

C:\dhcpsrv\

You should see files such as:

dhcpsrv.exe

dhcpwiz.exe

dhcpsrv.ini

wwwroot\

The configuration wizard is dhcpwiz.exe. This is what you'll want to run to build your network.


Step 4: Configure the DHCP scope

Run dhcpwiz.exe as Administrator.

In the wizard:

Select the server’s Field Day Ethernet adapter and press Next.


Then check HTTP Web Server and press Next. This will give you a browser-based status page.




Configure your DHCP address pool.

Example:


Start IP:      192.168.73.100

End IP:        192.168.73.199

Subnet mask:   255.255.255.0

Gateway:       192.168.73.10 (your FD server) or blank

DNS:           blank


Write the INI file into the same folder as dhcpsrv.exe. 

Step 5: Run DHCP as a service

Install DHCP Server for Windows as a service so when the machine starts up it will give out IP addresses on you FD network.

From an Administrator command prompt:

cd C:\dhcpsrv

dhcpsrv.exe -install -start

You can check the DHCP status page locally if HTTP support is enabled:

http://127.0.0.1/dhcpstatus.xml

This status page will show configured/operating connections and active clients.


Step 6: Test DHCP before Field Day

Connect a client laptop to the Field Day network.

On the client, open Command Prompt:

ipconfig /release

ipconfig /renew

ipconfig

You want to see something like:

IPv4 Address . . . . . . . . . . : 192.168.73.101

Subnet Mask . . . . . . . . . . : 255.255.255.0

Default Gateway . . . . . . . . : 192.168.73.10


Then test connectivity:


ping 192.168.73.10

If ping works, open N3FJP on the client and connect to the server.


Step 7: Add GPS time for offline accuracy

Since you have now created your own private network, internet time will no longer work. 

COAA’s GPSTime is a small freeware applet that corrects a Windows PC clock using GPS. It reads NMEA-0183 serial data from a GPS receiver and can make the PC clock accurate to the second. It works with any number of inexpensive USB GPS dongles you can get from Amazon.

GPSTime uses the GPS receiver’s $GPRMC sentence to determine UTC time, and it can either correct the PC clock once or keep running and update the time every minute.


Step 8: Configure GPSTime

Install GPSTime on the server.

Then:

Plug in the GPS receiver.



Confirm which COM port it uses. You do this by going into Device Manager and seeing what port comes up in Ports (COM & LPT) when you plug the device in. In the above example, it is Com4.

Open GPSTime


Go to Config.



Select the COM port.

Choose update mode.

For Field Day, I would choose:

Update every 60 minutes


Then press Start to make sure everything is working.

You can start GPSTime automatically by including /auto in the command line.

You can add a Windows Startup shortcut like:

"C:\Program Files\GPSTime\GPSTime.exe" /auto

Confirm the server clock updates correctly before you arrive at the Field Day site.



Step 9: Enable N3FJP TCP networking

On the server:

Open the N3FJP networking settings.



Select TCP mode.

Enable status/chat functions if you want the operators to see station status and messages.

Set the server/station name clearly and press Done.

On each client laptop:

Connect to the Field Day LAN.

Open N3FJP.

Go to the network settings.





Select TCP mode.

Enter the server IP or server name:

FD-Log-Server or 192.168.73.10

Give each client a unique station name, such as:

Station 1, Station 2, etc

or

CW

PHONE-1

PHONE-2

DIGITAL

GOTA

VHF

Log a test contact from each client.

Confirm the contact appears on the server and on the other clients.





Set the N3FJP server software to start on bootup. You do this by typing “run” into the Windows search box, then type shell:startup/click OK and placing a shortcut of the N3FJP program into the window.

Step 10: Keep the server and network on a UPS

This is NOT optional in my book.

Put the following equipment on a UPS:

N3FJP server PC.

Ethernet switch.

Field Day power is messy. Generators get refueled. Extension cords get kicked. Batteries sag. Someone unplugs the wrong thing by mistake. We all know what happens. 

A UPS gives the logging system a buffer. Even a small UPS can prevent the most annoying failure mode: the entire logging network rebooting because of a five-second power interruption.

Recommended physical layout

A sample Field Day layout:

                 GPS Receiver

                      |

                  USB / Serial

                      |

                [N3FJP Server Computer]

                192.168.73.10

                      |                      |

                Ethernet Switch

                 /     |      \

         CW PC   Digital PC

              /        Phone PC   GOTA PC

        Client laptops via DHCP

The server and client laptops should all be hardwired into the switch. 


Windows firewall notes

On the server, allow N3FJP and DHCP through Windows Firewall.



You can just turn the firewall off for all the networks since nothing will have internet access, unless you feel comfortable setting firewall exception rules.

For N3FJP clients, make sure to test BEFORE you get to the FD site. If clients cannot connect:

Temporarily disable Windows Firewall for the private network profile as a test.

If that fixes it, re-enable the firewall and create explicit allow rules. (or you can just leave it off for FD if you want).

Make sure all Field Day laptops are on the same network profile, preferably Private, not Public.

Do not wait until Saturday morning to discover that Windows thinks your Field Day LAN is a coffee shop.


Pre-Field Day test checklist

Do this at least a week before Field Day.

[ ] Server has static IP 192.168.73.10

[ ] DHCP service starts automatically

[ ] Client laptops receive DHCP addresses

[ ] Clients can ping 192.168.73.10

[ ] N3FJP server starts cleanly

[ ] N3FJP clients connect in TCP mode

[ ] Each station has a unique name

[ ] Test QSOs appear on all stations

[ ] GPSTime sees the GPS receiver

[ ] Server clock updates from GPS

[ ] UPS powers server and switch

[ ] Log backup process tested

[ ] Firewall rules tested

[ ] Spare Ethernet cables packed

[ ] Spare switch packed if available


During Field Day

Turn on the UPS.

Plug-in the switch.

Start the server.

Confirm GPS lock and correct time.

Confirm DHCP is running.

Start N3FJP on the server (if not set to auto start at boot).

Connect clients one at a time.

Log a test QSO from each station.

Clear your log for the event.

Back up the log periodically.


I would also create a simple paper sign near the server:

DO NOT POWER OFF

DO NOT CLOSE N3FJP

DO NOT UNPLUG NETWORK

SERVER IP: 192.168.73.10

It sounds silly until someone “cleans up” the operating table.


Backup strategy

At least once per every 3-4 hours:

Copy the N3FJP log file to a USB stick.

Copy it to another laptop.

Optionally export ADIF/Cabrillo during longer breaks.

Even if TCP networking is stable, backups are cheap insurance.

A good pattern:

C:\FieldDay2026\Backups\

  Club_Call-FD-2026-1200.mdb

  Club_Call-FD-2026-1600.mdb

  Club_Call-FD-2026-2000.mdb

Do NOT overwrite the same backup file all day. Use timestamps.


Troubleshooting quick hints


Client did not get an IP

Run:

ipconfig /renew

Check that:

Client Ethernet cable is plugged into the switch and you see network activity.

The DHCP service on the server is running.


Client gets an IP but cannot connect to N3FJP

Try:

ping 192.168.73.10

If ping works, check:

N3FJP TCP mode.

Server IP entered correctly.

Windows Firewall.

Is N3FJP running on the server?


Time is wrong

Check:

GPS dongle has a good sky view.

Correct COM port selected in GPSTime.

GPSTime is running in update mode.


Everything worked at home but not on site

Suspect:

Windows network profile changed to Public.

Firewall rule tied to the wrong interface.

Server not on its static IP.

DHCP server bound to the wrong adapter.

RF noise getting into the computer through the Ehternet cables (add toroids)

Someone plugged the LAN into another router that is also serving DHCP.


Final thoughts

A central N3FJP Field Day server does not need to be complicated. The key is to make the logging network boring, predictable and independent of the internet. You want operators focusing on making contacts instead of chasing IP addresses, messing with Windows time or wondering why the logging server disappeared when the generator hiccupped.

Treat the log server like a core service. Put it on clean power, label everything, test it before the event and do not let anyone “just reboot it real quick” unless the logging captain says so.

73 and Happy Field Day

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