[R-390] SWL antenna

[Roy Morgan]

At 07:37 PM 11/6/2006, Dan Merz wrote:
... I've been
>wondering about the transmission...reading about losses when mismatch 
>exists and thought maybe RG8 might be worthwhile.  Or...
>cheap 300 ohm foam twin lead that I now use.


Dan,

Consider these points:

- transmission line impedance matching is not very important in 
receive-only situations
- for multi-frequency listening (SWL) feed-line matching is not practical
- loss in coax due to mis-matching at HF over 100 foot runs is negligible
- your biggest challenge, and opportunity for improvement may well be 
combating locally generated noise
- coax has many advantages in combating noise from local sources
- coax varies in cost from *very* expensive to cheap. The most cost 
effective may well be cable TV coax: RG-6, and it comes at cheap (bad) or 
moderate cost (much, much better).

Here are my suggestions about what to do:

1) Download, print and read this document.  It tells about choke baluns, 
why you need some, and how to make them:
"Common-Mode Chokes" by
Chuck Counselman, W1HIS
<http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf>

2) Buy enough "RG-6 Quad" coax to make the run(s) you have in mind, and buy 
enough extra to wind some choke baluns out of the coax.  Get a few good 
crimp-on connectors and whatever fittings/adapters you need.

3) Put up whatever wire you can as high as you can, as far away from the 
house as you can.  Number 14 or 16 single wire is nearly invisible if it's 
away from the road or other folks who might complain.  Use thick fishing 
line for the end tie/insulator: it is invisible in and near any tree or 
bush.  Run the feedline from the antenna to the radio via whatever route is 
easiest.  Put some sort of choke balun AT the antenna end, in the middle if 
you can, and at the receiver end.

4) You did not tell us whether you have an R-390 (of whichever sort) or 
not.  If you do, also get a couple or three TV Feedline baluns of different 
sorts.  Try them at the input to the R-390 to see if they improve 
reception.  Fool around with grounds and the grounding of the feed line to 
see what works best.

(The following are partly tongue in cheek and partly serious. Do them if 
you can!)

5) Take all but one of the computers in the house out to the curb where the 
junk collector will pick them up. Cut off all power cords and monitor 
cables and get every one of the ferrite choke cores off the wires. Put the 
choke cores on your feed line, receiver power cord and the like.  The 
remaining computer should be under your control and turned OFF and 
unplugged when you are listening to the radio.

6) Send an email to W1HIS to add more information to his article about 
sniffing out sources of noise. In the meantime, use your portable radio to 
ferret out from your house every source of offending noise. Either cure the 
source or throw it out.  Keep in mind that some sneaky gadgets make noise 
even if they are turned off, while they are still plugged in.



Some miscellaneous notes:

The worst RG-6 TV coax you can find is available at Radio Shack and seems 
to cost $50 per 100 foot lengths (with connectors already on).  It may be 
the 92 percent shielded kind, and likely will let in any and all noise from 
your house and the neighbors, too.

The best such coax you can find can be bought at The RF Connection 
http://users.erols.com/rfc/index1.htm , "RG-6/QUAD CATV", for $20 per 100 
feet.  DUHHH!!  You can also get very nice connectors for it and adapters 
with the money you save.  This kind of wire is 100 percent shielded, has 
extremely low loss, and will last a very long time even outside.  They will 
be glad to put a GOOD crimp connector on one end (or both ends)  of your 
wire for you.

Having a roll of coax sealing tape ("B SEALING TAPE,1" x .030" x 30ft. #44 
Neoprene weather-proofing tape $3.00") is a very good idea for any 
connection outside.  The RF Connection also has insulators of many kinds.

Number 14 THNN (?) solid house wire in light sky blue color can be had at 
about $15 per 500 foot role at your local home store.  You can use it for 
antennas, grounding wires, and balun transformers if you care to make 
them.  After a year or so in the sunlight, the clear outer covering comes 
off but the stuff will work fine just the same.

(Note, I am a happy, and local, customer of The RF Connection.)

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
Phone 540-822-5911   Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-975-6097
roy.morgan at nist.gov --