Absolutely, Shawn, I'm 100% with you. Simplest is best and cheapest.
Have a reasonably long wire antenna of indeterminate length but with a
good earth (not ground) and you won't go wrong. You may be a few dB
lower than a dipole, depending on the orientation of the directional
dipole. Now for the good earth: you should dig a hole, say 1 x 1 x 1 m
in your garden, away from the eaves of the house. Buy a copper sheet,
say, 75 x 75 cm and 3-5 mm thick. Fix to one corner some 19-20 mm wide
copper braiding with a M8 brass nut and bolt, clamping well between
copper washers. You can even solder the braiding to the sheet, as well,
if you have enough horse power to take that lot up to ~200°C. Protect
the connection against corrosion with a good varnish (electrical
characteristics are not important). Lay the sheet in your hole and
refill with soil. Traditionally, you then piss on it. Run the copper
braiding BY THE SHORTEST POSSIBLE PATH up to the earth connection on
your Rx. Do not use power ground as an earth. An alternative to the
copper plate is an earth spike; this is a 2-3 m long copper (alloy?)
spike, about 30 mm diam but with a star profile (max surface area) that
you simply hammer in. Easier, but the sheet is better.
Such a system will give you excellent results at all frequencies,
especially if one end of your long wire is a few m higher or lower than
t'other end..
Remember dipoles have a cardioid directionality and you will get zero
reception along the axis of the wire, yes, zero.
Brian
On 28/02/2011 21:55, Upton, Shawn wrote:
> If I'm following the thread correctly, this is a receiver. If so, then
> just hook up wire--as a receiver it will not care so much about
> resonance and such. A dipole would work better, but really, a long wire
> and a good ground--or another wire acting as a ground--should allow
> reception. If you're not sure if the rig is working, I'd just hook wire
> up directly to it, get it receiving, then start worrying about better
> antennas--but quite a bit can be received on a simple few meters of
> wire.
>
> Multi-band dipoles do work, although the 40m antenna should work
> reasonably well for the 15m element, due to harmonic relationship. I
> believe 80 and 20 will do likewise. But I have done this sort of thing,
> but with inverted L's not dipoles. Just make sure to fan the legs out
> (look up "fan dipole" as this is what you are proposing to build). For
> straight receive I probably would not use a 1:1 balun, I like choke
> baluns better for feeding coax, especially for broadband unspecified
> impedance.
>
> Shawn Upton, KB1CKT
> Test Engineer
> Allegro MicroSystems, Inc
> [log in to unmask]
> 603.626.2429/fax: 603.641.5336
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Monday, February 28, 2011 2:41 PM
> To: [log in to unmask]
> Subject: Re: [TN] NTC: GEC BRT 400S
>
> Thanks all for help.
> I'm making a spider antenna (Rothammel), 6 beams
> 10 m = 2x2.5
> 15 m = 2x2.38
> 20 m = 2x5.05
> 40 m = 2x10.1
> 80 m = 2x19.8 m
> Will rig it in the attic with a 1:1 balun and RG-82 double shield down
> to
> the input and north-south direction. A multiband dipol with other words.
> What do you think? I've no idea about the Q and VSWR, nor Za
>
> Inge
>
>
>
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