OFDM is a strong signal mode for fast keyboard to keyboard communications and contrary to what we have been taught about digital modes we want o crank this one. With the very short transmit times you don’t need to worry about cooking your radio.
Across the front Range we will be using {14X.XXMhz} in Upper Side Band.
During Field Day 2025 on June 28th from 1400 to 1500 Mountain Time we will doing OFDM750F.
OFDM750F uses 750Hz of bandwidth. We are using USB instead of FM because in SSB you can recieve more than one signal at a time.
This is a joint effort between Colorado Digital, PRA and CRRG with SME support from W0SUN.
Currently only FLdidgi supports OFDM but before that you maybe even asking what is OFDM and that is a a very valid question. Without going into great detail about it here the short answer is it is Orthogonal Frequency Division Multiplexing. Well that didn’t help much lol read about it here and here. Basically we get to send messages very fast like less than 10 seconds fast.
So get your radios ready and prep for field day.
Check back here often for more updates and more information as it is added.
A comparison between Digital Modes and OFDM:
| Mode | Bits per Second | Time to Transmit the Phrase (S) |
| FT8 | 6 | 435 |
| JS8Call (fast) | 40 | 180 |
| PSK 125 | 125 | 7 |
| OFDM 750F | 1,125 | 3 |
| OFDM 3500 (9600 baud input only, SSB or FM 70CM minimum) | 5,250 | 1 |
The phrase is “the quick brown fox jumps over three lazy dogs” which is 376 bits, remember in FT8 and JS8 you only transmit for 12 seconds at a time, then recieve for 3 seconds.
yep it’s that fast.
Some tips on setting up FLdigi:
TX/RXid should be on
Phase should be 100%
Transmit should be centered on 1500Hz
When you “Tune” the ALC on your radio it should be between 7 and 8
Since you will be using full power be sure your antenna is tuned as good as you can get it, below 1.5 is ideal and using the highest gain antenna will also yield the best results. To reiterate this is not a weak signal mode. You need to squeeze all the efficiency out of your system at 2M.