For those who feel they really do need every last dB of signal (and most people don’t) we stock our highest gain FM antenna : the 6 element FM aerial. The aerial is similar to the 3 element version but has 3 more directors and is 6ft 10in long ! I would estimate that a 6 element FM aerial would give about 5 to 6dBd in gain.
Even if it were possible to obtain an FM aerial with more directors / gain it’s highly debatable whether the increased size and windloading of the aerial would be worth it in relation to any moderate increase in gain due to the law of diminishing returns.
Unfortunately FM6s are significantly bigger than just an FM dipoles which could be important in exposed locations. Furthermore the size / wind loading of multi element FM antennas can be problematic and they are not of the strongest construction either, particularly the directors and reflector. Lastly it is not generally practical to mount them vertically, though this is a bit irrelevant anyway because if fitting a multi element aerial then directivity is the whole point of the exercise *.
It should be remembered that whilst the 5 to 6dBd gain that a 6 element aerial gives you is certainly worthwhile in weak signal areas, it is the aerials’ directivity (i.e. its rejection of unwanted transmissions) that is possibly more worthwhile. These’s no escaping the fact that a 6 element antenna (particularly if it’s horizontally polarised * ) will give you a more reliable and consistent signal than any omni directional aerial. However directivity will obviously be a problem if you want to pickup more than one transmitter, and the vast majority of people don’t need a multi element FM (or DAB) aerial anyway.
* A vertically polarised aerial will be more susceptible to picking up off beam transmissions because to those broadcasts from the sides the antenna is effectively a vertical dipole. Or, put more simply, the aerial will be more directional if installed horizontally polarised.
Unfortunately a carrier length surcharge applies to this product.
We didn’t test the FM6 (we didn’t stock it when the tests were done ! ) , but I’d have thought its relative results for the table below would be :
FM directional performance – EXCELLENT plus
FM omni performance – Variable moderate to good
DAB directional performance – Moderate
DAB omni performance – Variable poor to moderate