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John Linsley Hood Quad FM Aerial for Troughline

Big John

Big John

pfm Member
After Mark the Ming (Mark Manwaring-White) improved my Leak/Paravicini Troughline stereo tuner I thought about the aerial.

I should explain my situation; I live in a top floor flat on a hill in North West London, there is no possibility of an external aerial, the communal one is OK but not for a Troughline which needs more signal,until now I have used a 5 element Antiference aerial in the loft. We have bought the loft and are going to add a couple of bedrooms etc, so it had to go.

I remembered an article By John Linsley Hood about a "Quad" aerial similar to those used by radio hams(apparently) I made the aerial from 4x 1' X 3' 1 MMM mild steel sheet with 1' cut off one of the panels as per the article shown at the end of his piece.

The JL hood aerial at 1 mm thick will fix flat to the woodwork of the roof under future insulation and wall board

I was charged £15 for the metal & £19 for cutting to size.

I put it together using heavy duty pop rivets with small PK screws for a 1/4" perspex panel to stiffen the 1" gap (see drawing in the article) I used 2 brass solder-less nipples soldered to either side of the gap to hold the WF 100 co-ax.

I have placed the aerial in the loft propped up for now it has not been optimised and already is an improvement by a margin for the carefully optimised 5 element aerial.

No hiss from the Troughline

http://www.mediafire.com/view/?sz8qxtc414666xu
 
Nicely done!

I have something very similar - a single loop of heavy gauge wire, about 82cm/side, on the edges of 3 shelves in one of my book cupboards for very similar reasons. It tapped the coax off one the corner to its effectively mixed polarisation. It's only abut 10degrees off axis for the notional line of sight to local 80w repeater and the reception is really good - well into full quieting via Onix BWD 1, even need to use the built-in attenuator on occasion.

It's also quite enough for my Quad FM1 or 3s too, which are rather less sensitive than the Onix. Cost of pennies, and very much more successful than other experiments with dipoles and copper j-poles in my location.
 
The neat thing about the JLH loop is that by using very wide conductors, it has a lower impedance than a wire loop of more conventional gauge, giving a better match to coax across the band, and hence another dB or two of performance.

It also has truly negligible self noise, which is nice, but not really useful because the noise floor in the FM band is way above the thermal floor.
 
Good point - I know the wire is not optimal, even a pretty bad match but fortunately I'm < c.2miles from the repeater. And I can reach through to get books out!

I'll have to try the 'plate' version...
 
Wasn't there a version that had ally foil strips, wallpaper pasted to a bit of hardboard? That would cost pennies.
 
You can make a loop with coax, calculate the length and connect the coax end core to the braid at the junction.

The loop can be circular or square, both work and are much less detuned by nearby material than a Yagi-Uda
 
stevec67 said:
Wasn't there a version that had ally foil strips, wallpaper pasted to a bit of hardboard? That would cost pennies.
Click to expand...

Yes JLH used a foil one in the article he states his later solid was better.

I have read of foil stuck to a plastic table cloth and simply hung where needed.
 
I recall that article from the first time around... I remember liking the fact that the capacitance in the overlap of the sheets meant that 'good' connections weren't essential.

Have to read it now...

Paul
 
I ran a foil one for years with good results until someone gave me a "proper" FM aerial can't say I noticed much difference.

Pete
 
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