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Does height matter?


#1

In an effort to answer this vexing question, I carried out an extensive single test with Colin G8JSM this afternoon. Raising the antenna from 1 metre to 3 metres gave a noticable improvement on 2m FM from Easington Fell. On the basis of this single data point, the case is proven beyond reasonable doubt.

73

Richard
G3CWI


#2

In reply to G3CWI:

Hi Rich,

I’m going to do the same from an array of summits over the coming months… I’ll report back.

All the best,

Rob G7LAS


#3

In reply to G3CWI:

Which type of antenna did you use?

Heinz


#4

In reply to G3CWI

As a matter of interest although it could have been due to my location.
When I lived on Pye Green, Cannock (which I wish I still did)I could not hear the Cornish Beacon on 2m but by raising the antenna which was on the apex of the house by another three feet I was able to.

73 Graham G4JZF


#5

In reply to G3CWI:

The real question is not “does height matter”, it is “at what height does small further increases stop making a significant improvement?” Raising the antenna from one to three metres must make a significant difference, raising it from three to five metres will probably make less difference and five to seven metres will likely make a negligable difference.

73

Brian G8ADD


#6

In reply to G8ADD:

I’m 5’ 8"

I’ve never really found it a problem.

73 es Happy Easter.

Mark G0VOF


#7

In reply to G0VOF:

But were you wearing flat,s or platforms ,it does matter as you might fall.

Those extra 3 inches could make all the difference…!!!


#8

In reply to M6EPW:

It says that G4UXH wasn’t receiving a direct signal but a reflection.

It should be noted that with a J-poles main lobe being 16 degrees above horizontal, better performance can be had by activators by mounting the J-pole upside down on their support. But only if they are situated at a suitable elevation ASL in the first place.

Or probably more easily achieved is tilting the support to 16 degrees off vertical and then rotating the tilt to the direction of the chaser.

Andy
MM0FMF


#9

In reply to MM0FMF:

It should be noted that with a J-poles main lobe being 16 degrees
above horizontal, better performance can be had by activators by
mounting the J-pole upside down on their support.

ROTFL


#10

In reply to G3CWI:

ROTFL

You mean it should be mounted horizontally and rotated about its axis? :o)


#11

In reply to G4AZS:

Of course that raises another issue: has anyone tried using a slim jim horizontally?

Anyway, in respect of the original findings, raising a 144MHz antenna from 1m to 3m will have a significant effect as it takes it beyond a wavelength above ground. Thereafter the law of diminishing returns comes into effect. Interestingly though, at 1297MHz, holding the antenna at arms length above head height rather than just in front of me does make a significant difference, though I suspect the result is enhanced by the fact that the antenna is further away from my body mass.

73, Gerald G4OIG


#12

In reply to G4OIG:

But where is ‘ground’? On a rocky summit it’s probably not where your feet are.


#13

In reply to G4OIG:

has anyone tried using a slim jim horizontally?

Doesn’t that make it a short fat Jim?

73 de Les


#14

In reply to G4OIG:

In reply to G4AZS:

Of course that raises another issue: has anyone tried using a slim jim
horizontally?

=)


#15

In reply to G3CWI:

Coincidentally, I have spent a few hours yesterday and today experimenting with a slim jim - made with 4mm stranded copper wire, taped onto a length of plastic trunking. The final dimensions are close to published designs, and I am reasonably confident that it is resonant. The SWR is fairly flat across 2m, lowest around the middle of the band.

Now to compare it with my basic ground plane, made by soldering a quarter wave length of cadmium copper wire to the centre of an SO239 socket, and 3 radials to the outer. SWR adjusted by altering the angle of the radials. I’ve used this on all my activations so far.

With the base of the antenna about 2m above ground in each case, the ground plane gets me into the Stoke repeater (from Shrewsbury) with 2 bars of signal strength showing on the rig. The slim jim does not hear the repeater.

Raising them each in turn on a 5m fishing pole - the ground plane now hears the repeater with 5 bars on the display, and so does the slim jim, also showing 5 bars. For comparison, my commercial colinear five eighths over five eighths, at the same height, displays 8 bars.

In a garden environment with trees and houses around, the slim jim seems to respond to a change in height in a more complex way than the ground plane. I have no means of getting them any higher, but I may tidy up the slim jim and test them in more open surroundings.

In the absence of any 450 ohm feeder, my plan was to sandwich a wire slim jim in between two layers of duck tape, but I haven’t tried that bit yet…

Adrian
G4AZS


#16

Well, here’s my 2¢ worth…

Does hight matter? Well, I certainly don’t drag 15ft of poles up a summit for the fun of it… I don’t think antenna height is an option on a summit, I think it’s essential.

For SOTA activations and for a some extra effort, (this is purely my own opinion,) a half decent collinear will blow a J Pole out of the water.

Of course, YMMV…

I’ve just spent 1hr 40mins on a cold, wet and miserable G/SP-011 Freeholds Top, after handballing my Colliner and poles on a fairly long walk.

This is a difficult VHF summit, where the take-off leaves a lot to be desired.
However, I managed 35 contacts on a very quiet day with the collinear, 15ft of poles and a Hand Held, the best contact being about 110 miles, with Dave G7CNM/P in Lincolnshire.

73 Mike
2E0YYY


#17

In reply to 2E0YYY:
Hi,Mike pleased all the effort you put into the activation payed off you really were a strong signal on the Lincolnshire Wolds look forward to working you again soon. 73 Dave
G7CNM


#18

In reply to 2E0YYY:
Hi,Mike pleased all the effort you put into the activation payed off
you really were a strong signal on the Lincolnshire Wolds look forward
to working you again soon.

Hi Dave,

To say I was surpised to here you must be an understatement! Very restricted summit as far as VHF take-off goes. Excellent contact.

Best 73
Mike 2E0YYY


#19

In reply to G7CNM:

Yeah… good to work you today Dave from Black Hill.

Unfortunately you were my only contact despite the 10 mile walk in hideous conditions! Activation failed!

Rob G7LAS


#20

In reply to G7LAS:

Yeah… good to work you today Dave from Black Hill.

Unfortunately you were my only contact despite the 10 mile walk in
hideous conditions! Activation failed!

Black Hill has a lousy reputation for VHF take-off Rob and you get a really depressing walk thrown in.

Only just qualified it the first time I activated it (broken feeder) :frowning:

73 Mike
2E0YYY