# Can I mount my RX and VTX antennae next to one another?

I've heard that it is bad practice to mount a 2.4 GHz RC receiver antenna next to a 5.8 GHz FPV VTX antenna because the transmitting antenna will negatively impact the receiving antenna's reception. For example, this is said to be true in this Rotor Riot video at 1:40.

Is this true? If so, how close is too close and how can I mount the two antennae to minimize the interference between the antennae?

The distance is dependent on the wavelength of the lowest frequency. You can calculate the wavelength $$\lambda$$ (m) from $$\lambda = c \div f$$, where $$c$$ is the speed of light in a vacuum (ms-1) and $$f$$ is the frequency (Hz.) Taking the centre frequencies of the ISM bands we get:

2.4 GHz: $$\frac{299 792 458 }{ 2 450 000 000 } ≈ 0.12 = 12 cm$$
5.8 GHz: $$\frac{299 792 458 }{ 5 800 000 000 } ≈ 0.05 = 5 cm$$
(Quick 'sanity check' tip: 5.8 GHz is about twice 2.4 GHz, so we expect the wavelength to be about half; looks good.)

The smallest separation is usually recommended as a quarter of the longest wavelength, which for 2.4 GHz is only 3cm - quite manageable. That said, greater separation helps so put them as far apart as your frame practically allows.

• Perfect! Do you have any resources to cite for your 1/4 λ figure?
– ifconfig
Jun 7 '20 at 16:35
• 1/4 λ is what I learned reading/studying for HAM test. I think it is common knowledge in the radio world. Aug 24 '20 at 15:10
• That's for not screwing up the radiation pattern, though. I'm rather skeptical about it working to reduce RFI. Jan 4 at 0:08