Featured: DX Engineering 400MAX Low-Loss Coax Assemblies at DX Engineering.
This is an affiliate link: Hood's Finds may earn a commission from DX Engineering at no extra cost to you. We have not tested this product; the specifics below come from the product listing.
Builders spend a lot of effort squeezing clean power out of an amplifier, then hand it to a feedline that quietly turns part of it into heat. The more power you run, the more that loss matters in real terms, and the more a poor connector or tired cable can fail. The DX Engineering 400MAX PL-259 coax assemblies are low-loss, dual-shield cables sold with connectors already installed and tested.
Where feedline loss comes from
Coax loses power in two main ways: resistance in the conductors, and energy absorbed by the insulation between them. Both get worse as frequency rises and as the cable gets longer. Loss is quoted in decibels per length at a given frequency, and DX Engineering lists 400MAX at 0.8 dB per 100 ft at 30 MHz.
Because a decibel figure is a ratio, the power lost scales with the power you feed in. A small loss figure is a small fraction, but at amplifier power levels that fraction is real heat in the cable and real power that never reaches the antenna.
What the construction does
- Center conductor. A 10 AWG stranded bare copper conductor offers less resistance than thinner cable, which cuts conductor loss.
- Foam dielectric. The gas injected foam polyethylene insulation is partly gas, so it absorbs less energy than solid plastic. It also gives the cable a higher velocity factor, listed at 84 percent, meaning signals travel through it faster than through solid polyethylene cable.
- Dual shield. A bonded aluminum tape shield with 100 percent coverage sits under a tinned copper braid with 95-96 percent coverage. Better shielding keeps RF on the inside of the cable and outside noise out, which helps with RF getting into station equipment.
- Jacket. The UV-resistant PE Type III jacket is listed as suitable for direct burial.
Why a pre-made assembly makes sense
Double-shield cable with a foil layer is more demanding to terminate than ordinary single-braid coax. Connectors meant for soldering to a simple braid are the wrong choice for it, and a badly installed connector can undo the benefit of good cable. These assemblies come with silver-plated brass PL-259 connectors installed, and DX Engineering states that every assembly is continuity and Hi-Pot tested, then weather-sealed with heat shrink. They are sold in multiple lengths, so you can buy the run you need.
Stated limits
The listing is clear about two uses to avoid: 400MAX is not recommended for VHF/UHF duplex repeater applications or for a beam antenna rotator loop. If either applies to your station, choose a cable designed for that job.
A note on power and legality
Low-loss feedline matters most for licensed amateur stations running amplifiers within their legal limits, which top out at 1500 watts PEP under FCC Part 97 and are lower on some bands and license classes. External linear amplifiers are not legal for use on CB radio. Good cable is worth having at any power level, but it does not change those rules.
Where to get it
Check current price and availability: DX Engineering 400MAX Low-Loss Coax Assemblies at DX Engineering.
This is an affiliate link: Hood's Finds may earn a commission from DX Engineering at no extra cost to you. More picks on the gear page.
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