Advice please on installing the Bob Archer antenna Model 6

[Richard Mole]

I have had good experience with one of these in my D18 for many years.
So now I'm trying to develop a scheme for fitting one into a much smaller rear fuselage.

The instructions with the antenna state that it may be bonded onto the curved internal surface of a rear fuselage. But I wonder what the limits on the degree of curvature might be?

The lower 55% of the antenna would not be curved in any way. But the upper 45% is curved progressively more and more steeply so that the top of the antenna is as good as horizontal.

The height of the antenna when straight is about 683mm and this reduces to a projected height of 603mm for my scheme.

All I know for sure is that the model 6 is described as a 'folded up' dipole to minimise the vertical dimension for vertical polarity. Will the thing still resonate as intended if the projected height is 88% of its length?

A counsel of perfection would be to install it and then test !

Failing that, are there any knowledgeable antenna specialists out there who would hazard an opinion please?

[ColinC]

Hi Richard,

For entirely different reasons I have been reading Bob Nuckold's book. "the AeroElectric Connection" which I suspect you are already aware of. That has a chapter an antenna design and I found it made a lot of sense to me.

He seemed to suggest that a dipole can have its ends folded quite drastically without great detriment and I think gives an example of one in his loft. You may gain some reassurance from reading that chapter.

I can't add anything as my only experience with radio was at the Grammar School Radio Club (G3KZA) using old ex RAF R1155's and similar valve jobbies with a great long wire aerial.

Anyway, here's a link to the book in PDF form which I think is a great read for any home builder: http://www.aeroelectric.com/Book/AEC_R12A.pdf

Regards,

Colin

[tnowak]

Some old style metal VHF whip antennas are bent back at angles of 45 deg or more (sometimes a bit of the antenna is near horizontal) and they still work okay.
No guarantees offered of course (!) but I would think your Model 6 antenna will still work okay in the orientation described.
Tony Nowak

[Richard Mole]

Thanks to you Colin and Tony for your replies.

The Bob Nuckold book is a useful resource which I hadn't seen before. If I remember right it used to sell at a fairly high price (before the internet really changed the business model perhaps).

And Bob Archer's own 'tenna tips is helpful too.
http://www.aeroelectric.com/articles/An ... rcraft.pdf

But some of the underlying technologies are going to remain a closed book for me at any rate
https://sportcraftantennas.wordpress.co ... -antennas/

I think it is worth going ahead as planned for the reasons you both gave. Its also perhaps a case of the dog that didn't bark - nobody has come back to say that they had tried something similar and had a bad experience.

[Frank Parker]

Richard, your comments about inside a fuselage obviously cannot apply to a metal airframe, or even carbon fiber, perhaps. I cannot see how the curvature can have an effect if the antenna is mounted in what is essentially a non-conductive enclosure.

[mcfadyeanda]

The full length of the aerial is only needed to tune it to the frequency (band). The lower c.1/3 to 1/2 of the arm of the aerial does most of the radio energy transmission, so that bit needs to be vertical (+/- 15 deg) in order to provide the required vertically polarised signal, the rest can be folded.
I have a Bob Archer in a curved fibreglass rear fuselage (not so tightly curved as Richard's, it sounds) and SWR's are less than 2. Reception of transmissions are not an issue at 1.5W power (except occasionally straightahead where engine/crew attenuate radiation.

Duncan Mcf

[Richard Mole]

Frank,
you are absolutely right; it will be mounted in a ply-covered wooden fuselage so in effect a non-conducting enclosure. Glad to hear you are going strong. I have a vivid memory of watching you hand-propping a very reluctant VW in a single-seat a/c (unsure what) at Fairoaks, I think, in the early 60's !

Duncan,
thanks for the input and clarification. Its good to hear that you obtained an excellent result.

So I'll stop agonising over technical matters that I don't really understand and install the antenna paying careful attention to the detail like supporting the coax properly and in-line with the feed point.

As a last request for advice, could I ask what to use by way of preventing moisture from eventually corroding the feed-point attachment? What would you recommend ? I guess there is some non-setting compound or other I could get from say Maplins?

[Frank Parker]

Richard, had to be my Turbulent. My present ride is an AA5 with a Skytech starter that fires up with no effort on my part in the hot Florida weather!