Is RG-8X the General Purpose Coaxial Cable?
While doing a presentation about choosing the right coaxial cable, someone suggested that RG-8X (also called “Mini 8”) might be the best general-purpose cable for amateur radio. There is a lot to like about RG-8X. It is about 1/4-inch in diameter, and is flexible and affordable. This comment made me realize that I default to a larger cable (LMR-400 or RG-8) for everyday use and consider RG-8X as the cable for lightweight, portable applications (such as SOTA and POTA). But perhaps I am underestimating the capabilities of RG-8X.
So let’s take a look at the specs on RG-8X, using the DXEngineering RG-8X datasheet. Other manufacturers of RG-8X will have similar specs.
Most general-purpose amateur radio operation occurs at power levels of up to 100 watts for frequencies of 3 MHz to 54 MHz and up to 50 watts from 144 MHz to 450 MHz. I am thinking in terms of a station that has a 100-watt radio for HF and 6m and a typical 50-watt FM dual-band radio for 2m and 70 cm.
These power levels are easily handled by RG-8X. In fact, the cable is spec’d for over 1 kW for all of the HF bands. At 50 MHz, the power rating drops to 900 watts and further reduces to 400 watts at 150 MHz. DX Engineering does not specify the power at 440 MHz, so I looked at other websites and found that the power rating drops off to about 100 watts. So power handling is not going to be an issue.
Signal loss may be a more significant limitation. How much loss are we going to be comfortable with? That is difficult to answer because each of us may make different tradeoffs to accomplish our radio operating objectives. As an upper bound, I hate to see the cable loss go as high as 3 dB, which corresponds to losing half the power in the cable! But living with 1 dB might be acceptable, which is 20% power loss. So let’s use that.
(Someone reading this is thinking: 3 dB is only half an S-unit, it won’t matter that much. To which I say: it won’t matter unless you are operating near the noise floor and 3 dB is enough loss to have your signal disappear.)
The table above shows the loss in dB per 100 feet. At 100 feet, the loss creeps up to 1.5 dB at 30 MHz. Let’s stretch our 1 dB rule of thumb to 1.5 dB, which means the loss is reasonable for all the HF bands using a 100-foot cable. At 50 MHz, the loss increases to 2.3 dB/100 feet, so to stay within 1 dB or so, we would need to limit our cable length to 50 feet. At 150 MHz, the loss rises to 3.8 dB/100 feet so we should keep our cable length less than about 25 feet. We don’t have a spec for the loss at 450 MHz but checking other websites reveals a typical loss of 6.6 dB/100 feet at 400 MHz. A 25-foot cable at 450 MHz will have a little over 1.6 dB loss.
So now the problem becomes clear: signal loss at high frequencies will be the limiting factor. (This is why I tend to grab a larger cable because I’m often operating above 50 MHz.)
So what can we conclude in very broad terms? Is RG-8X a good choice for a “general purpose” coaxial cable? I am going to say “Yes, But”. The key issue is signal loss and that is driven by the frequency being used and the length of the cable. So Yes, RG-8X is a good general-purpose coaxial cable but watch out for signal loss and cable length at high frequencies.
Here’s my Rules of Thumb for this cable:
For HF, RG-8X is great for all bands with cable lengths of 100 feet (maybe longer).
For 6m, RG-8X is good with a cable length of up to 50 feet.
For 2m and 70 cm, RG-8X is good with a cable length of up to 25 feet.
In all cases, checking the manufacturer’s specs and doing your own calculations is recommended. For a slightly deeper look at coaxial cables, see Hey, Which Coaxial Cable Should I Use?
73 Bob K0NR
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Power handling might not be a problem but the higher loss might be, especially in QRP.
Tnx for the skinny on the use of RG8X in the range of amateur operating frequencies. It makes logical sense for making decisions regarding permanent and emergent transmission line considerations. Line loss has always been a nemesis for all operators, especially with the worsening QRN from environmental sources.
TNX, Norm WB8AEO