Directional antennas, angle of reception, and rotators

Hi all,

I’ve decided it’s time to try a directional antenna for my NAT02 and 03, replacing my MD ST-2, which is just ok.

However, I don’t want to go all the way to including a rotator - it’s just a bridge too far.

What I’m curious about is how wide an angle of optimal reception is in a directional antenna (recognizing maybe hard to generalize). I have a couple of broadcast antennas that are within about 20 degrees of each other - wondering if I aim the antenna midpoint between them, if I’ll still get top reception for the associated stations.

Any thoughts?

What are you intended to receive, normal commercial broadcasts or are you thinking about DXing.
I would avoid a ‘broadcast’ antenna, but that’s depending on type. Do you really mean you have reception antenna’s? Can you describe it please, brand and model would be good.
Normally all you need is a 3 element, or maybe more if you are far distant, horizontally mounted Yagi.
Where do you live and how far do you want to reach out.

A couple of typical FM broadcast band Yagi antennas within 20 degrees of each other with 3 or so elements or less (plus dipole) is roughly going to provide a good field strength of 40 degrees either side of the average direction between the two.(plus/minus 30 degrees per antenna)

I would only consider a rotator or alternate antennas if you wanted to receive optimally transmitters greater than 45 off the optimum direction.

To be more accurate and not finger in air you need to look at the antenna design, frequency/station, and height above obstacles/location… the maths is too much for this website … but there are some free field strength tools… but you need several input parameters to plot reasonably accurately.

Of course the general rule the higher the gain, that is the more elements, the more directional and the narrower the main gain lobe. By contrast a single dipole has a figure of eight gain pattern.

The Ron Smith Galaxie G-17 used to be recommended by Naim for its tuners, but supply has been erratic since the said Ron Smith decided to move to Spain, or somewhere. I have no idea what the current situation is.

They’re still going IIUC, still in Luton, check their website. Ron passed away, over 10 years ago IIUC, it is still run by the family now, also IIUC. There was a piece on their website about this I read a few weeks ago, but cannot find it there now.

Here’s my post, with the quote anyway:

There is some mumbo jumbo about broadcast VHF antennas at both ends of the scale - you really don’t need exotic metal work unless you are in extreme conditions - such as strong local side interference, lots of tall building/reflectors around you, you need a significant front to back ratio to filter out an interfering station from behind you or you are wanting to receive DX (70 mile plus) , your tuner front end is not particularly effective or your major stations of interest are at the extreme ends of the band and not in the middle.

So yes if you are hearing fading, obvious stereo distortion or birdies (high frequency warbling distortion) then yes you might need a more exotic antenna - otherwise a three or four element Yagi is going to be absolutely superb on a quality tuner for a transmitter up to 35 miles or so away - and in most urban environments a two element or single dipole can be fine. Remember FM is wonderfully resilient - its just it can get horrid in extreme conditions as above or occasionally when Ionospheric ducting or reflections extends (sporadic-E) the range significantly of stations and causes cross station interference. Some times there is nothing you can do to prevent distortion here - but is not common and most likely in spring and autumn.

However as with all antennas it needs to be fitted properly with a proper antenna rigger - perhaps not your average Digital TV aerial installer. It needs to be properly directionalised - and mounted sufficiently in the clear (ie away from chimney and roof top). If it’s within around 2 metres you are starting to compromise the performance of the antenna. Bear in mind the larger and more exotic the antenna the greater the wind loading so the bigger the aerial support structure. Standard Yagis are not too bad with wind loading.

The other important consideration is the downlink and a balanced to unbalanced converter if not built into the antenna. Compromises here throw signal away and also with regard to the Balun compromise the antenna field strength pattern, make the coax more lossy and susceptible to interference along its route from domestic electrical noise sources.

Again a qualified and proper aerial installer will/should know all about this. If some one says what’s a balun or it is not required and is not built into the antenna (and you are using coax) - get somebody else.

In the grand scheme of things none of this is difficult - but get it wrong and you are wasting your time using a well designed antenna… and yes I hold an Ofcom radio licence for antenna installation and operation.

Blake UK and Antiference do some effective and reasonably priced FM directional antennas with minimal wind loading

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