Re: antennas

--- In [email protected], Dave Martindale <dave.martindale@s...> 
wrote:
> 
> >  From: Dan Jacobson <[email protected]>
> >Subject: rubber ducky antenna not good enough for shortwave
> >
> >Apparently the stock rubber ducky antenna is OK for 144 and 490 
Mkz,
> >but wanting to hear the shortwave and AM broadcast bands, not up to
> >par.
> 
> It's designed to work well on the 144 and 440 MHz ham bands (the 
same 
> antenna is used on the IC-Q7).  If it works at any other 
frequencies, it's 
> just an accident.  In fact, the R2 antenna *does* pick up AM 
broadcast 
> signals at around 1 MHz well enough to listen to local stations, 
which is 
> amazing.  My other amateur dual-band antennas are absolutely 
totally deaf at 
> that frequency.
> 
> >So, what shall I connect up in its stead?  On condition though, say
> >that you are determined to use household items to construct it and 
not
> >buy it ready made.
> 
> For shortwave, the simplest antenna is a long piece of wire.
> 
> >BTW, Though I have managed to cobble together a SNA to coax 
connector,
> >slipping a metal tube over the rubber ducky seems like a way to
> >"connect another antenna" without removing the rubber ducky.
> 
> Poor idea.  Slipping a tube over the rubber antenna will 
capacitively couple 
> some signal into the antenna element.  But the rubber antenna isn't 
just a 
> piece of wire; there is almost certainly a matching network in the 
base of 
> the antenna (that's why it's larger in diameter).  That matching 
network 
> isn't designed to pass signals at shortwave frequencies, so it 
probably 
> won't pass much of the signal.  Just take the rubber antenna off.
> 
> >Another idea for connecting antennas on the fly to enhance the 
rubber
> >ducky would be to whittle off the rubber at the tip of the ducky 
until
> >one reaches the coil, and then alligator clip various things to 
that.
> >However this is probably a road to ruin.
> 
> Same problem as above.  The antenna is not just a wire.
> 
>         Dave


I agree that the idea of whittling off the antenna top isn't a great 
one, though its possible the R2 antenna is just a basic loaded coil. 
I have disassembled, built and rebuilt lots of ducks for scanners, 
h/t's etc, many with oversized bases are built like that just to 
accomodate the hardware that hooks them to the radio (i.e., the 
connector). But you still run the risk of having whatever inductive 
load the duck consists of cause signal strength nulls throughout the 
frequency spectrum. You could likely map the nulls with a grid-dip 
meter to see if they were in undesirable areas of the spectrum, by 
why go to the trouble?

A much simpler, sensible idea is to connect a longwire antenna to the 
antenna jack, the same as any shortwave reciever would use. I use the 
same one I built for my shortwave radio (which does a much better job 
than the R2, but I often do reception comparisons as an equipment 
check). You need only feed the wire to a center conductor of an SMA 
connector and connect it to the R2 directly (with the duck removed). 
In my case, since I have the wire fed to a UHF coax connector, and I 
have a UHF-female to BNC-male adapter connected to the SMA to BNC 
adapter I bought from Grove Enterprises for the R2. I connect the 
shield side of the coax to a water pipe as a noise ground, but have 
found it works prettly well even if you use only the center feed.
Works great for me, with signal reception comparable on the SW bands 
to my shortwave radio in AM mode (though having SSB mode on the 
shortwave makes it my reciever of choice for this band, obviously).

A side note: since the pickup area on a longwire is much larger than 
the duck, you can have two problems from using one with the R2: 
signal overload/harmonics from nearby stations, and static discharge 
damage from nearby lightning strikes. In the first case, you can use 
the attenuator to help, but you obviously will reduce the signal you 
wanted to hear as well as the problem signal, which defeats the 
purpose of using the bigger antenna. Using a shorter wire as a 
compromise may alleviate this. The second issue, static damage, is 
common with sensitive recievers built today. You don't have to have 
your antenna actually hit by lightning to detroy your radio's front 
end circuitry; lightning within a few miles will do just fine. You 
can buy lightning and static protectors to mitigate this, but they 
are not always reliable, so the best idea is to never connect the R2 
during a storm to a longwire. Also, always ground the antenna for a 
moment before connecting to the R2, in case of any capacitive buildup 
on the wire.






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