Planning Regs

[surefm]

Question: Is there anyway that a FM broadcast antenna be built to be within planning regulations of being up to a metre in length ?
Is this even possible ?
Thanks Mick

[Albert H]

Not really.

The minimum size for any kind of effective aerial is going to be a quarter-wavelength (about 75cm at 100 MHz), and that would require either a counterpoise of the same length (making it into a dipole) around 150cm long or it would need a ground plane, ideally tilted away from the ¼-wave vertical, and an absolute minimum of 75cm all 'round.....

Theoretically, you could make a 3/16ths vertical, but the match would be horrible, and you'd still need a counterpoise or a ground plane.

A friend of mine concealed a ⅞-wave vertical with a loading coil, coax balun and a ¼-wave counterpoise inside a 6cm diameter flagpole! It was installed on top of a department store, six (nearly seven) floors above the street, with the rig and link receiver concealed in a fire hydrant box with a false bottom on the roof below. The builders who installed it for him buried the coax in the asphalt, and the link receive aerial was an ordinary Band IV TV Yagi. That set-up was used very successfully at weekends for a few years and gave pretty good coverage over the city and the very flat surrounding countryside. The rig was discovered when the company that owned the store were doing a power usage audit and couldn't understand why there was about 400 Watts unaccounted for!

[yellowbeard]

Antennas like the pentrator, cycloid or rototiller are all 800-900mm tall but I don't reckon you could mount them on such a short length of mast. Your real problem with such a limited space is getting the antenna away from the roof and mast - a long boom might help but it would make the antenna want to twist around the mounting pole in strong winds. If I had your problem I would probably build a (horizontally polarized) halo antenna and stick it right at the top of my 1 Metre pole - it's not ideal but it might be worth a try. You could knock a test version up out of stiff wire and hook a low power transmitter to it to see how it gets out and if the SWR is manageable.
https://en.wikipedia.org/wiki/Halo_antenna
The amateur radio sites are full of how to build this antenna for their frequency bands, they also have plans for a square version that is easier to build called a "squalo" - google it and see.
Seeing as we are talking ham radio and planning permission, years ago in practical wireless a ham wrote in a letter saying that he had been refused planning permission for a mast - his neighbour was a witch and the mast interfered with her flight path to Salisbury plain...

[SundayGroover]

Planning permission?? Has been a nightmare lately - our (legal) station has been granted a second FM frequency and do you think we can get permission to put the kit anywhere? Planning and conservation officers thwarting every poxy move we make!

[surefm]

I have issues with my next door neighbour, at the moment I've been raising and lower my mast so it's not at full height at all times, when I told the planning people about this they said she would look into this, this was before this covid 19 started, looking at the regs it said no more than 2 antennas or dishes to one property, and no more that a meter in height or width/ length for each antenna without planning permission , overall height including masts not to be I think 400mm above ridge or chimney whatever highest, if I read it right, I've been using a 5/8 wave at 87.7, which in itself is a no go

[surefm]

I like the reply about the flagpole antenna from albert, might put a jolly roger on it, but thank you for all replies, will investigate it further . Mick

[surefm]

I like the reply about the flagpole antenna from albert, might put a jolly roger on it, but thank you for all replies, will investigate it further . Mick