Coax Cable Loss Testing - 21st January 2026
25m RG-213
15m Ultraflex 7
25m LDF4-50
Click any plot to enlarge
Measured using Signal Hound SA44B spectrum analyser, 10 MHz - 2 GHz sweep
Above are loss against frequency plots for three different bits of coax measured at the testing evening of the 21st January 2026. All the cables were close to the manufacturer's specifications; the only problem spotted was a high loss around 2.4 GHz for the LDF4-50, which proved to be an easy to correct problem with one of the plugs.
| Coax | Loss per 10m (dB) | Loss per 25m (dB) | ||||
|---|---|---|---|---|---|---|
| 144 MHz | 432 MHz | 1296 MHz | 144 MHz | 432 MHz | 1296 MHz | |
| RG-213 | 0.82 | 1.27 | 2.90 | 2.06 | 3.17 | 7.13 |
| Ultraflex 7 | 0.76 | 1.37 | 2.66 | 1.90 | 3.42 | 6.65 |
| LDF4-50 | 0.23 | 0.40 | 0.74 | 0.57 | 0.99 | 1.84 |
For a convenient calculator using the manufacturer's figures see The DX Shop Coax Loss Calculator.
How much loss is acceptable?
1 dB loss means 79.4% of the signal will get through. This loss relative to no loss at all will generally go unnoticed in most QSOs. Only in very marginal contacts, e.g. EME, could it make a difference.
However, 3 dB is a whole S-point on most rigs and so will be significant on any weak <S3 QSO, with half the signal lost in the feeder.
You should try to keep your feeder loss below 1 dB on all bands by using the appropriate coax. This means if you have 25 metres of feeder you are going to need LDF4-50 or better on 432 MHz.
So, what can you do if this is not practical? Fit a masthead preamp on RX and either increase TX power to compensate for the loss, or have a masthead power amp.