FM Aerial Configuration - Advice Needed

[Bartman]

I recently bought an 8 element Blake aerial to feed my NAT01 (a Ron Smith would be unacceptable to Mrs B, this tested her tolerance!). The signal strength is improved but I just want to check I’ve assembled it correctly - there were no instructions and website questions have remained unanswered.

The aerial came with 7 elements to screw into the chassis to make up the dipole, 2 of which are reflectors. They all look the same but 2 of the elements are slightly longer. Using the photograph from the web page I put the longest at the front and back of the main element, but is this right? Perhaps the 2 longer ones should form the reflector. I’d be grateful for advice from any Fishermen who understand aerial design.

 

[hifinutt]

put some pics up on here

 

[boon]

I recently bought an 8 element Blake aerial to feed my NAT01 (a Ron Smith would be unacceptable to Mrs B, this tested her tolerance!). The signal strength is improved but I just want to check I’ve assembled it correctly - there were no instructions and website questions have remained unanswered.

The aerial came with 7 elements to screw into the chassis to make up the dipole, 2 of which are reflectors. They all look the same but 2 of the elements are slightly longer. Using the photograph from the web page I put the longest at the front and back of the main element, but is this right? Perhaps the 2 longer ones should form the reflector. I’d be grateful for advice from any Fishermen who understand aerial design.

Is it an FM8, or ABM8?

 

[Bartman]

 

[Bartman]

Is it an FM8, or ABM8?

An FM8.

 

[Al M]

Looks wrong to me. From my distant memory of FM antenna theory, the two longest elements are the reflector and should go behind the dipole, then the shorter elements in reducing length order to the end of the antenna. Someone may correct me if I'm wrong!

 

[boon]

An FM8.

Not sure, but looking at Blake website photos I would have thought that from the left of your photo as fitted, elements 4&5 need swapping over. Their instruction manual is quite crap for the 8

 

[colasblue]

The two longer bits should be in the H shaped reflector at the back I'd have thought, but the picture suggests they should be the first two elements in front of the dipole.

 

[Bartman]

The website photo isn’t very helpful, my memory not without fault (as boon stays I had elements 4&5 the wrong way round) but logic suggests the 2 longer ones should be the reflectors so I’ve swapped them round and will report back once the tuner settles down. Still open to suggestions. I’m not far from the main mast or the local booster, but have trees in gardens around me so went for a more powerful aerial to improve the signal. My main station is R3 which I could receive quite well, but now the signal is better and other stations illuminate both triangles on the NAT01.

 

[Big John]

Best internet photo I could find, of a similar aerial.

 

[seagullsnacker]

Nope

The two longest should those on the reflector at the right hand side of the pic.

So from the right hand side H as it were longest (the reflectors), then the folded one (driven element) then progressively shorter as it goes to the left hand side (directors)

It looks from the pic like you have (from the left hand side) the two Reflectors elements at points 1 and 5...they should be at the end on the right hand side.

Measure them to ensure you end up shortest through to Driven Element then longest at the reflector side

Hope that helps.

Paul

 

[Bartman]

Just heard back from Blake and they said the configuration seagullsnacker and colasblue suggested is correct. Why they couldn’t include a simple diagram is bewildering, but many thanks to all who replied with advice.​

 

[boon]

Just heard back from Blake and they said the configuration seagullsnacker and colasblue suggested is correct. Why they couldn’t include a simple diagram is bewildering, but many thanks to all who replied with advice.​

Would have been good if an engineer had assembled the one on their website instead of getting the cleaner to do it.
Glad you got it sorted though.

 

[seagullsnacker]

The weird thing is anyone with any familiarity with beam antennas should know - I would expect manufacturers too but not necessarily your average HiFi enthusiast - I only know cos I’m a Radio Ham as well

 

[2ManyBoxes]

As well as what's in front of the aerial when pointing at the main transmission mast, don't forget what's behind

Reflections can be a big factor. As an extreme example, my bungalow is right next to a 2 storey house which is also slightly upslope from me. Unfortunately the transmitter is directly in the opposite direction.

Even with a Ron Smith aerial taller than me with a huge spread of a tail, I got more birdies than a turkey farm from the signal bouncing straight back off next-doors wall. Had to abandon the idea in the end.

 

[seagullsnacker]

Beams can be designed for maximised gain, or front to back rejection - often it’s the former over the latter but it’s always a compromise between the two..also gain is a function of boom length rather than elements but it’s all physics rather than foo

 

[Bartman]

I’m amazed the difference it makes to the SQ (not just lack of hiss, birdies etc). More richness to the tone, depth and lateral separation. Cheapest upgrade I’ve had in a while!

 

[davidsrsb]

As well as what's in front of the aerial when pointing at the main transmission mast, don't forget what's behind

Reflections can be a big factor. As an extreme example, my bungalow is right next to a 2 storey house which is also slightly upslope from me. Unfortunately the transmitter is directly in the opposite direction.

Even with a Ron Smith aerial taller than me with a huge spread of a tail, I got more birdies than a turkey farm from the signal bouncing straight back off next-doors wall. Had to abandon the idea in the end.

I have had stronger reflected signal than direct - it can happen, especially at UHF rather than VHF.
Reflector panel antennas are better than Yagis when you want good front to back

 

[Craig B]

Here's the 'Assembly and Fitting Guide' that Farnell has up for the Blake range.

https://www.farnell.com/datasheets/3670015.pdf​

 

[Mike Reed]

Bit late to this thread and the assembly conundrum has been solved (longer reflectors at the back of course) but does this mean you have to bring the array etc. down to correctly assemble it and would this be you or a (costly) aerial rigger?

Had an Antiference 8 element in my college days and that was the only time I've (or, rather, my Pioneer TX tuner) suffered from birdies. My R.S. Galaxie 23 didn't manage the move from big Victorian house with 5 lovely chimneys to a '60s house which was built with sand instead of cement. Still got a load of (new, spare) elements in my loft !

O.P., wonder why you didn't use a 12' thick-wall alley or steel mast to boost height (as I have here with a 6 element antenna; erected for previous 01). Maybe chimney not quite man enough? Not sure mine (another 60s house) is here, t.b.h.