El 05-05-13 13:57, Tom escribió:
Thanks for the advice.
The 2m 70cm old antenna someone gave me is a Diamond X200 I believe.
It is about 2.4 meters long with a connection in the middle. It was
full of water and for many years, I took it apart yesterday and
emptied the water and green stuff out and sanded the entier top part
of the element and coils. I will de-oxit it and put it back together
and seal it better. I cannot get the bottom length of antenna out of
the fiberglass shell so I will leave that greenish but I noticed there
was continuity between the outside shield of the S0239 connector and
the antenna and not continuity between the center of the Coax
connector and the antenna. I thought the center coax would connect
with the antenna and the shield would connect with the gnd planes. Is
that normal?
From the center of the SO239 connector on the antenna there is no
continuity between anything. Only continuity between the threads of
the SO239 and the antenna length. After I put it all together I will
use the AV600 meter to tests its SWR with the 2m70cm rig to see if it
is ok.
That bottom fiberglass piece looks glued in there pretty good I don't
want to break the seal , I think the water might be getting in from
that half way connector.
Can this antenna be modified for broader band scanner use? Most of my
interests in the scanning will be the marine bands (156 ish megs) and
VHF and UHF ham bands anyway.
Thanks gents for the advice,,,
73s
Hello Tom,
I don't know the internal construction of your antenna, but when SWR
turns out to be good on 2m and 70cm, the antenna is very likely good
and can be used for reception, but on 2m and 70 cm only. As Jeff also
said, these antenna are narrow band and performance on VHF marine band
will be well below that of a simple halve wave dipole tuned for VHF
marine. It does not mean it receives nothing, but you only hear
nearby stations on the 2m/70cm antenna when tuning your scanner to VHF
air or VHF marine.
If you want one antenna that fits all, go for the discone, or even
better, go for the biconical antenna. I fully agree with Jeff, the
biconical dipole has better radiation pattern for your application.
When you enter biconical cebik into a search engine you may find
useful info on biconical antennas if you plan to construct your own
antenna. As your VHF and UHF bands of interest have around 3:1 ratio,
VSWR will be good enough for reception.
Wim
PA3DJS
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"Ralph Mowery" wrote in message
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"Tom" wrote in message
...
Hi
I have the Realistic Programmable scanner with 200 programable
channels. A lot of range there like 6 m, 2 m, 70 cm, marine, etc
etc etc, wide range.
I want to put up an external antenna that I can hook it up to its
own BNC connection for external antenna. I believe the higher the
better.
Which is better to run a bare copper wire longest and highest to
connect it to the BNC center? Or should I use coax and splice the
center copper feed to
You will not receive much with a long bare copper wire.
Get some coax, rg8x is good, the rg 6 type is also good and usually
cheap. Don't worry about the 70 ohm impedance of the rg-6 as the
impedance is not going to be 50 ohms anyway over much of the
frequecny range. The lmr400 type is beter, but I doubt that you will
notice the differance if the length is around 100 feet or less. Not
worth the big price differance for a scanner in many cases. The only
problem with the rg6 may be the connectors as the shield is usually
aluminum or a material that will not take solder. The crimp
connectors are fine.
For the outside antenna, a discone type is often used. Really for a
broad band reception any ground plane or colinear will probably give
you good reception over a wide band. After all, the short antenna
that usually comes with the scanners often pick up many signals.
--
Wim
PA3DJS
www.tetech.nl
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