Most RF hobbyists know the Nyquist‑Shannon sampling theorem: sample at least twice the highest frequency to avoid aliasing. But few realize that the same principle applies to your choice of coaxial cable – especially when you work with 4G, 5G, or LoRa at 868/915MHz.
Let’s connect sampling theory, cable attenuation, and real‑world field performance.
A quick refresher on Nyquist (the right way)
For a band‑limited signal, the minimum sampling frequency is:
f_s > 2 * f_max
If you violate this, high‑frequency components “fold” back into the passband – that’s aliasing. A 100MHz signal might appear as 10MHz, and the damage is irreversible.
Now think of your coax as a “sampler” in the frequency domain. It doesn’t sample in time, but it attenuates higher frequencies more than lower ones. That’s the skin effect: as frequency goes up, current crowds toward the conductor surface, increasing effective resistance.
The attenuation formula every RF guy should know
Cable attenuation (dB per 100ft) is roughly proportional to √f and √(resistivity). In practical terms:
Attenuation (dB) = k * √f * length
At 100MHz, a typical RG174 loses about 10dB per 100ft. At 915MHz (LoRa, Helium), that jumps to over 30dB per 100ft. At 2.4GHz (WiFi), it’s even worse.
If you run 30ft of RG174 from your Bobcat miner to a rooftop antenna, you lose nearly 90% of your signal power before it reaches the air – equivalent to turning a 5.8dBi antenna into a negative‑gain dummy load.
Why cheap cables “alias” your signal
When a cable attenuates high‑frequency components much more than low‑frequency ones, the received spectrum gets distorted. It’s not true frequency folding, but the effect is similar: fast edges are smeared, modulation quality (EVM) degrades, and your SNR collapses.
This is why your Helium miner’s witness count drops from 30 to 12 after switching to a long, thin cable. The high‑frequency content of the LoRa chirps never makes it to the antenna.
The solution: low‑loss coax + proper length management
For sub‑1GHz bands (LoRa, Helium, GMRS), you need a low‑loss cable. BOOBRIE’s LMR200‑equivalent upgraded cable features triple shielding and a larger center conductor than RG58. It achieves a velocity of propagation of 83% (RG58 is only 66%). At 915MHz, its attenuation is only ~0.8 dB/10ft – far better than RG174 (2.5 dB/10ft) or RG58 (1.3 dB/10ft).
Here’s how they compare:
| Cable Type | Attenuation (dB/10ft @ 915MHz) | Max length for <3dB loss |
|---|---|---|
| RG174 | ~2.5 dB | 12 ft |
| RG58 | ~1.3 dB | 23 ft |
| BOOBRIE LMR200‑equivalent | ~0.8 dB | 37 ft |
For most homes or small farms, 37ft is enough to go from an indoor gateway to a roof antenna. If you need longer runs, you can compensate with a higher‑gain antenna or a low‑noise amplifier – measure your path loss first.
Don’t forget connectors and adapters
A poor connector adds insertion loss and increases VSWR. BOOBRIE’s full‑copper gold‑plated SMA↔TS9 precision adapters are made for hotspots that come with TS9 ports (like Netgear Nighthawk M5/M6, Cudy P5). Even if your router uses a non‑standard interface, our adapters make it work with our LMR200 cables.
Real‑world example
A Helium miner was using 25ft of cheap RG174 to connect his rooftop 915MHz antenna. His witness count stayed between 8 and 12. After switching to BOOBRIE LMR200‑equivalent cable + an SMA‑to‑TS9 adapter, his received signal strength went up by 6 dB. Within three days his witness count climbed to 24. He saved the cost of a new miner.
Your action checklist
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Measure your cable run – include vertical rise and horizontal distance.
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If the run exceeds 15ft, ditch RG174 – go with LMR200 or better.
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Check your router’s antenna ports – if they’re TS9, get an adapter beforehand.
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Keep both MIMO cables the same length – avoid phase mismatch.
🔌 Ready to upgrade your coax?
BOOBRIE offers LMR200‑equivalent low‑loss cables with SMA male or female connectors, available in custom lengths. We also carry SMA↔TS9 precision adapters to solve interface mismatches.
📡 Not sure how much cable you need? Contact our support – tell us your equipment distance and frequency band, and we’ll help you calculate the link budget.
