advertisement


DIY FM Dipole - Trials and Tribulations

Hi,

In reply to some of the points raised above.

Regular coax would not be the cheap crappy coax, however that maybe an error on my part not specifying the type.

At the frequency given, the number of elements will have more of an effect than the boom length, however as a radio ham myself this is just as interesting a discussions as HIFi cables.

A more simple solution for the OP might be to find out where his local radio club is, when and where they meet, go along and have a chat, radio hams have a long record of helping people out with issues like this, you never know he might end up liking the hobby and becoming one.

I would agree that making a DIY antenna is a great idea, radio hams have been doing this for years, and often getting better results than mega expensive professional made antennas.

The most important part when placing an antenna outside is that the feedpoint, where the coax is connected to the antenna, is made fully waterproof, if done correctly the joint will remain watertight for many years, 10 to 20 years is not uncommon.

Cheers

John
 
G T Audio said:
Getting a few quotes for an aerial installation would be sensible to make sure you are not being ripped off. It might be that the price quoted is the going rate these days and it might not be a rip off! I would image that aerial installers these days must be a dying breed...

Just to clarify, no way on earth will a DIY or indoor aerial solution be as good as a proper set up roof mounted aerial.
Click to expand...
As I read it, no one on this thread has imagined that an indoor will equal a roof mounted, except, possibly...
 
"Equal" may depend on circumstances and how it is judged. Here an internal dipole works fine if placed with care. But we are up a hill with a decent line of sight to the TXs. And can use a decent FM tuner. Have a couple of home-made FM dipoles in the loft that I put where they got a high level, to feed two rooms.

Indoors DAB also works from damp string... if 'works' is confined to listening to some speech radio. Problem there isn't reception, of course. In this case I just wound some wire around a wooden stick to make the dipole. Then perched it on a cupboard.
 
The signal isnt string enough for the Leak Troughline, its borderline on old Rotels RX402/602/802. Seems to work ok on Nad 402, 412, 4155 and surprising well on the meridan 104 too. Works best on the Hitachi FT5500 digital thingy, but that is very sensitive. Thnk I might to revisit a rewire to the roof in the summer BUT this simple dipole is well worth a try if all you are using is a ribbon aerial or similar.
 
If you can't fit roof aerials, it's worth thinking about putting them in the loft. I live in a house with line of sight to the local relay transmitter abot 2 miles away. I've had success with 2 x UHF TV and 2 x VHF FM DIY installations in the loft space. They last forever. The FM aerials are about thirty years old. The only thing outside, also a DIY installation, is a Freesat satellite dish. Having said all that, I guess the Firestick renders the whole lot obsolete :)
 
Eyebroughty said:
At the frequency given, the number of elements will have more of an effect than the boom length
Click to expand...
Some of the extreme gain values claimed by the very complex Ron Smith Galaxies are questionable.
Making any high gain antenna broadband across the entire 88-108 MHz band is challenging.
Often "stacking" a couple of lower gain antennas is better

Lofts are good so long as you don't have a foil backed insulation up there
 
Last edited:
davidsrsb said:
I have no idea what the VK2ABQ is, but a Moxon is a well known compact antenna, rectangular with a gap on each side
https://www.qsl.net/dk7zb/Moxon/Moxon.htm
Click to expand...

Thanks for that. Makes me want a copy of his book as well! :) I have the books by Kraus which are excellent, but more academic than practical for DIY.

I'm still puzzled by the idea that inherently that gets "less man made noise". AIUI antennas can fiddle with the pattern, so you might get to put *specific* noise sources into a dip or null. But there is no magic way it can reduce overall noise from all the surroundings regardess of direction, yet get the signals without the same loss from those same directions. So its really a question of good matching/balance and how the noise background might vary with direction relative to the source direction when choosing an antenna pattern.

That tends to mean a long pole can move the antenna away from noise sources in houses below, so reducing their off-beam solid angle and thus noise input. Relying on the directionality to aid this.
 
A closed loop has no high impedance open ends to pick up some out of band interference sources, which might cause front end overload if you don't have a preselector. HiFi tuner front ends are very crude designs
 
There is some debate if the original idea is not Fred Caton's, VK2ABQ, however Les Moxon, G6XN in his book HF Antennas for All Locations descibes how you can modify the VK2ABQ by changing the spacing between the two elements to give a slight advantage over the original idea that used coat buttons.

However if you read what the title of his book is called, HF or High Frequency, I would suggest it would not be useful for VHF or Very High Frequency, which is of course where the FM frequency range is as it has very little gain over a dipole.

The antenna that uses a similar system at VHF and HF to the VK2ABQ is the Skeleton-Slot Antenna that has two yagi antenna connected to the slot, one above and one below the slot antenna radiator, similar to stacking yagis.

G R Jessop, G6JP describes the VHF version in his book VHF, UHF Manual.

This is not even taking into account the OP's location, issues of direct and reflected signal paths and what type of antenna at what height would be best suited for that location.

Some discussion in the links below, you can make your mind up on who came up with the any of the ideas first and if they are going to make any difference over whatever your preferred antenna is.

If you think HIFi can generate lots of debate wait until you get into radio!

http://on5au.be/content/a10/moxon/mox20.html

https://www.instructables.com/Skeleton-Slot-yagi-Stack/

https://groups.io/g/RSGB-Workshop/topic/78249334
 
eguth said:
I recently had a good Ron Smith aerial mounted high on the roof stolen in the middle of the night. Silently.
Click to expand...

Unbelievable. They must have been in their element !

I have enough elements from my G23 (spares I bought) in my loft to construct sth resembling an antenna; not that I'm likely to do so. I used to fill the connection box on the various aerials I've had with wax; seemed a good idea at the time! My coax is black computer cable or sth like that; 75 ohm but superior to the old brown stuff. Friend bought a 100 m drum a few years ago (as I was going to rewire) and I've still got 30 to 40 metres in my loft; shame, but never got round to it. 2 x h/d rotators and multi-core cable as well; a memory of my G23 days on Victorian chimney overlooking the channel in Ramsgate. Good old Ron (and son).

Unfortunately, my current 60s chimney can only manage a 6 element on a 12' mast but it still pulls in sufficient signal from the Xmitter 9 crows' miles away. I've had 8 element Antiference etc in a big loft but as G.T. says, there ain't any substitute for a high positioned exterior antenna.
 
[QUOTE="Mike Reed, post: 4815386, member: "Unbelievable. They must have been in their element !

Good one


Your best laugh yet.
Cheered me up.
Wonder what tuner u use? A GT one, roof mounted?
 
eguth said:
Your best laugh yet.
Click to expand...

You must've missed the others, then:D

eguth said:
Wonder what tuner u use? A GT one, roof mounted?
Click to expand...

Was NAT 101 when I had the G23. That wouldn't fit on my next house, which is a pity, because I upped it to an 01. Sold that to a Chinese national (for export) in '19, I think after it had been fully serviced. Bought a £25 NAD from eBay and started listening to radio more. Couldn't believe that a tuner, which cost 1025 less than my 01's sale, could equal it as a sum of the parts.

Maybe my 6 element wasn't good enough for the 01? Who knows but I listen to R3 and 2 on a regular basis, whereas I didn't with the 01.
 
You must log in or register to reply here.


advertisement


Back
Top