[Antennas] 70 Mhz (4 meter) antenna (long)

Tue, 22 Jan 2002 17:41:47 +0000 (GMT)

Hello Frank et alia,

I am suprised no-one from the UK has replied to this already, but now 
I have some time, I will !

The 70MHz band has been available to hams in the UK since November 1956,
and as a result lots of designs have been published for gear for the
band. However, as it is only available to the UK, GJ, GU, GD, ZC4, ZB2
EI and recently S5 the market has been limited and therefore the amount
of kit produced commercially has also been small.

Modern designs for 70MHz gear are relatively sparse. I'll skip
radios/tvtrs etc as we are on an antennas list (!) and stick to the
questions posed.

The UK band is from 70.0 to 70.5 MHz. We are limited to 160w at the
antenna. I also will assume that people will want multielement designs
rather than gp antennas that are easily scaled.

In the commercial arena there are few UK manufacturers that produce
monoband 70Mhz yagis. Take a look at www.vinecom.co.uk or
www.moonrakerukltd.co.uk for an idea of those available (there are
others - try RADCOM for adverts). Aside from 50 to 144 MHz LPDAs, as
far as I know there are no directive antennas that cover 50 and 70Mhz,
although Jaybeam of Northampton used to produce a 4el trapped version
some years ago. Anecdotal evidence suggests that this wasn't a great
antenna though. 

On the homebrew front there are some designs around, although I'm not
sure how many have been through the strict computer testing that is now
available. I have built monoband yagi designs from the VHF/UHF dx book
(ed g3sek) which are computer optimised and seem to be OK for me in the
major contests. I can scan the pages and send these to anyone who
is interested. M1CCZ has an interesting design on his web pages that has
also been computer generated. See www.qsl.net/m1ccz for info. There is
plenty of software around that will help you roll your own if thats what
you fancy. There are also some interesting log-yag designs by g3fdw
that have great claims (published in RADCOM), but I am unsure how well
these work in practice. I am unaware of any modern quad designs for
70MHZ (anyone put me right ?).

Dual band homebrew designs are even more of a challenge to find. As far
as I can remember there aren't any new 50 and 70MHZ designs around with
NEC (or similar) optimisation. I have tried several antennas on my
*very* restricted London plot for both bands. These include two yagis on
the same boom (NBS design) with interlaced elements. Qualitatively I am
happy with this, but quantitatively I suspect it could do with some
work (design available if I can find it). However now I use a G3FDW
log-yag on a 5 ft boom. This is a 50-70Mhz log cell with 2 dir for 70MHz
and a single director for 50MHz. Again I am happy with it as it suits my
needs, but "could do better with more effort" as my teachers used to
say. This design was in RADCOM, and I cant put my hand on that design at
the moment, but if anyone wants it I can look harder. 

I havent seen a dual band quad around at all. Perhaps the nice people at
cubex could help there with a modern design (grin).

I think thats about all. All of that is from memory, so is hardly cast
in stone ! If you are interested in the 70MHz band, take a look at
www.70mhz.org. The site doesnt have much new info on it, but will help
anyone get started. There are plenty of G's with the 70MHz capability,
but the lack of DX means the band is under-used (like 220 Mhz in NA
?). For those who have wide band multimode scanners (or rig) and are
also enjoying the F2 on 50Mhz at the moment, I would urge you to knock
together a dipole / 2el of some description and call for x-band contacts
when 6m is belting towards the UK. I am told that an x-band G to VE
contact was made in 1979, so why not now ? Signals on six have been
amazing.

I hope this has been of some use, if anyone wants designs or info pse
get in touch. I look forward to hearing you on the air. Especially if I
am transmitting on 70MHz......

73 es GL
Steve
M0BPQ
Ps all typos and spelling errors are just to keep you awake. SB
-------------------------------------------------------------------
Dr Steve Bunting
Neural Damage and Repair,		Tel 0207 848 6268
Neuroscience Research Centre,		
King's College London
Hodgkin Building			[email protected]
Guys Campus
London Bridge
London
SE1 1UL
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On Tue, 15 Jan 2002, Frank, ZS1CM wrote:

> Greetings from the bottom end of the African Continent....
> 
> We have now access to this new band in ZS-land. Although we surely are not
> the only country with such privileges, I have seen no design info for
> antenna's or combined antenna's for 70 MHz.
> 
> OM Etienne ZS6Y recently asked for info on a 6/4 meter combo yagi, for me
> the most likely combination.
> 
> Any comments or suggestions ??
> 
>   From the desk of :
>   Frank DAELEMANS ZS1CM
>   P.O.Box 415
>   GREEN POINT
>   8051
>   South Africa
> 
>   tel/fax/voice mail +27 21 434-3698
>   SMS 0825117337
>   e-mail          [email protected]
>   ham e-mail only  [email protected]
> 
> 
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> 
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