Antennas near one another?

[Pedro_The_Swift]

I plan to add an external GSM antenna on the rear of the caravan,, can I put a AM/FM antenna within say 300mm of it?

[Alex 110]

Can't see why not - the frequencies used are quite different.
I used to have a 27mHz cb antenna & HF tapped whip 10cm apart on my bullbar with no issues.

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[Lotz-A-Landies]

More importantly the GSM phone isn't putting out a lot of power.

I would think twice about putting a 100W HF very close to another antenna, just because of the potential RF energy being emitted.

[slug_burner]

If you can locate the antennas further apart it will be better. You will get a hole in your radiation pattern, the phone will have a weaker signal coming from/going to a direction, most likely that of the other antenna.

[Pedro_The_Swift]

I have very limited roof space available,,(behind the rear hatch, in between the two solar panels) if I can stretch it to 450 will that be better?

also, will a cable run of over 5metres be bad for the am aerial?

[Lotz-A-Landies]

If I understood correctly, the other one was a receiver only antenna, so shouldn't interfere greatly with the GSM antenna, in fact it would have minimal impact on the propagation of the phone signal.

[AndyG]

Should not be a problem, and 450 is better than 300. Just look at the array of high powered antennae on some Towers

[Alex 110]

5m cable run should be no problem at all assuming you will use a quality coaxial cable such as rg6. Installing terrestrial tv antennas & foxtel satellite installations I regularly run 20m+ of rg6 & the signal drop over that distance is mimimal (foxtel at dish signal strength 85, MER 14, at wall plate over 20m of cable signal strength 81, MER 13).
Sorry it I've got too technical.

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[md90]

300mm is an acceptable distance, general rule of thumb is to keep them at least 1/4 of a wavelength apart, which for the GSM (lowest band) is 35cm, so you're almost a full wavelength apart. If anything it may slightly reduce the performance of your FM/AM antenna but this will be negligible.


use a quality coaxial cable such as rg6.

Just to clarify, you don't want to use RG6 or RG59 or similar for the GSM antenna as the impedence is 75Ω for TV, you want to use low loss RG58 (foam coax) or LMR195 which has a 50Ω impedance and keep the run as short as possible. The RG6 is OK for the AM as stated.

[slug_burner]

If by AM you are referring to the broadcast band approx 530 to 1600 kHz then it will not matter what length or type of coax you use as the wave length is so long that the length of coax will appear very short, the antenna and receiver impedance are likely to look more like an open circuit than the characteristic impedance of 50 or 75 ohm coax.

The loss in cable increases the higher the frequency, the loss will be minimal in the cable at AM broadcast frequencies.

I will leave the spacing of antennas to the experts, with the information we have at the moment I am only prepared to say the further apart the better. I have seen many arrays with more than a 1/4 wave length spacing produce nulls (reduced gain) and gain peaks that is with both driven and parasitic elements.

[Pedro_The_Swift]

Thanks everyone:clap2::BigThumb:

The cable from the GSM will have to run less than a metre, most of that downwards. The wireless modem it connects to will be mounted inside the rear of the van.