Newbie Scanner Antenna Questions

Newbie Scanner Antenna Questions

Post by daniel we » Fri, 06 Aug 1993 00:37:42

--
I recently bought a portable scanner that I would like to use in my
home with an external antenna rather than the short wick antenna it
came with.

Can anyone give me advice on antennas.  What are the advantages and
disadvantages of the different types.  Can I build my own?  Any
problems putting the antenna in my attic?  What cable to use - I've heard
RG-6/U is a good lower cost substitute for RG-8.  What about RG-58?

The frequencies I will listen to are 30 to about 900 MHz.  Can this
be covered adequately with one antenna?

Thanks in advance,

-- Dan

----------------------------------------------------------------------------

              "My comments are my own, not my employer's"

 
 
 

Newbie Scanner Antenna Questions

Post by jeffrey.n.jon » Fri, 06 Aug 1993 01:50:24


I am trying to use Mininec and a Smith chart program to learn more
about my G5RV and antennas in general. The problem I am running into
is they both seem to want the resistance and reactance of the antenna
which is part of what I am trying to find out. I am reading through
the ARRL antenna book and it did have a small chart on dipoles up
to about 65% of a wavelength that showed the a resonant dipole to
be about 70+j28 (is the symbology right?). However I am trying to
find out what it would be for a 3/4 wave dipole or any other length
that I might want to try out. What is the best way to go about finding
out this information? Thanks and 73!

Jeff

--
 Jeff Jones  AB6MB         |  OPPOSE THE NORTH AMERICAN FREE TRADE AGREEMENT!

 Infolinc BBS 510-778-5929 |  Want to guess how many we'll lose to Mexico?

 
 
 

Newbie Scanner Antenna Questions

Post by Tom Bod » Fri, 06 Aug 1993 03:12:03

|>
|> --
|> I recently bought a portable scanner that I would like to use in my
|> home with an external antenna rather than the short wick antenna it
|> came with.
|>
|> Can anyone give me advice on antennas.  What are the advantages and
|> disadvantages of the different types.  Can I build my own?  Any
|> problems putting the antenna in my attic?  What cable to use - I've heard
|> RG-6/U is a good lower cost substitute for RG-8.  What about RG-58?
|>
|> The frequencies I will listen to are 30 to about 900 MHz.  Can this
|> be covered adequately with one antenna?
|>
|> Thanks in advance,
|>
|> -- Dan

--
A discone is a good wide coverage antenna.  The original design of the
discone lacked good coverage for 30-50 Mhz.  Grove (and others) sell a
version which has a "top hat" for 30-50 Mhz.  Radio Shack sells a discone
but I don't think it has the low band top hat.

Don't scrimp on cable to save money.  Pay the extra for RG8, particularly
if you expect to run over 25 ft or expect to listen above 400 Mhz...

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Tom Bodoh - Sr. systems software engineer, Hughes STX, N0Y?? (in the mail)  +
+ USGS/EROS Data Center, Sioux Falls, SD, USA   57198     (605) 594-6830      +

+       "Welcome back my friends to the show that never ends!" EL&P             +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 
 
 

Newbie Scanner Antenna Questions

Post by (Mikey Likes » Fri, 06 Aug 1993 06:03:42



>--
>I recently bought a portable scanner that I would like to use in my
>home with an external antenna rather than the short wick antenna it
>came with.

>Can anyone give me advice on antennas.  What are the advantages and
>disadvantages of the different types.  Can I build my own?  Any
>problems putting the antenna in my attic?

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^This sounds like a job for:
DISCONE....

I'm in a similar situation, just having aquired a R/S Pro-39, so I went
back through all my old QST's and '73's.  Score: QST nada, '73: BINGO!
I'd have to go back and look for the issue#, but it was built out of $20
in parts from the hardware store.  And the author was building it for his
attic.  The only catch was that his only goes from 144MHz to 1296MHz--not
down to 30MHz, as both you and I need.

Then I was looking through my 1991 Radio Works catalog (mostly baluns, and
wire ant. stuff...) and there it was: CAT # D-16 Discone Scanner Antenna,
for the sum total of $29.00...Still nor down to 30MHz, only 100MHz, but
claims to go up to 2.5GHz. (Radio Works is at 804-484-0140, fax only, or
BOX 6159 Portsmouth, VA 23703)

The only off-the-shelf discone that goes 30-1300MHz is the Diamond D130J,
which is apparently being discontinued.  The cheapest I found it for was ~
$76.95 at National Tower Co. (I don't have their #, but 800-555-1212 should,
and they advertise in QST.).
They said that they had a few left as of Monday, 8/2)....  What seems
to distinguish the Diamond discone from all the others I've seen is a vertical
element, on-axis, attached to the top of the disc--presumably this gives the
antenna the extended low-end?  And, a discone will give a good enough match
on all the amateur frequencies that it covers to allow acceptable xmit as well.

If someone has/knows of plans for a discone that has the bandwidth of the
Diamond D130J, I'd like to know about it--please.
(just my $00.02...)

Quote:>What cable to use - I've heard
>RG-6/U is a good lower cost substitute for RG-8.  What about RG-58?

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^How about RG-8x (mini-8)?

>The frequencies I will listen to are 30 to about 900 MHz.  Can this
>be covered adequately with one antenna?

>Thanks in advance,

>-- Dan

>----------------------------------------------------------------------------

>              "My comments are my own, not my employer's"

--
Michael Dahl/KC6UFR
 
 
 

Newbie Scanner Antenna Questions

Post by Dave Roge » Fri, 06 Aug 1993 20:49:05


|>
|> The only off-the-shelf discone that goes 30-1300MHz is the Diamond D130J,
|> which is apparently being discontinued.  The cheapest I found it for was ~
|> $76.95 at National Tower Co. (I don't have their #, but 800-555-1212 should,
|> and they advertise in QST.).
|> They said that they had a few left as of Monday, 8/2)....  What seems
|> to distinguish the Diamond discone from all the others I've seen is a vertical
|> element, on-axis, attached to the top of the disc--presumably this gives the
|> antenna the extended low-end?  And, a discone will give a good enough match
|> on all the amateur frequencies that it covers to allow acceptable xmit as well.
|>
|> If someone has/knows of plans for a discone that has the bandwidth of the
|> Diamond D130J, I'd like to know about it--please.
|> (just my $00.02...)

Grove and Universal catalogs both have discones with the vertical
element for extended response down to 30 MHz.  (~$80)

Radio Shack sells a good one to which the vertical can be added.  (~$60)

|>
|> >What cable to use - I've heard
|> >RG-6/U is a good lower cost substitute for RG-8.  What about RG-58?
|> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^How about RG-8x (mini-8)?

Use RG-8X.  Low loss.  Easy to work with (~ same diameter as RG-58; no
need for F connectors).  Cheaper than RG-8.  I use marine grade RG-8X
since the summers destroy the *** (or plastic?) coating on coax down
here in Texas.

===============================================================================
Dave Rogers                                            
M & R Software, Inc.

On contract to: NEC America, Radio Software Dept

If you can't see the sky from where you work it's time to change jobs.

 
 
 

Newbie Scanner Antenna Questions

Post by Tom Bod » Fri, 06 Aug 1993 21:30:00




|> >...
|> >Can anyone give me advice on antennas.  What are the advantages and
|> >disadvantages of the different types.  Can I build my own?  Any
|> >problems putting the antenna in my attic?
|> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^This sounds like a job for:
|> DISCONE....
|>...
|>
|> The only off-the-shelf discone that goes 30-1300MHz is the Diamond D130J,
|> which is apparently being discontinued.  The cheapest I found it for was ~
|> $76.95 at National Tower Co. (I don't have their #, but 800-555-1212 should,
|> and they advertise in QST.).
|> They said that they had a few left as of Monday, 8/2)....  What seems
|> to distinguish the Diamond discone from all the others I've seen is a vertical
|> element, on-axis, attached to the top of the disc--presumably this gives the
|> antenna the extended low-end?  And, a discone will give a good enough match
|> on all the amateur frequencies that it covers to allow acceptable xmit as well.
|>
|> If someone has/knows of plans for a discone that has the bandwidth of the
|> Diamond D130J, I'd like to know about it--please.
|> (just my $00.02...)

The discone that Grove (1-800-438-8155) sells for $80 has a top hat to give
it 30-50 coverage...

--
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Tom Bodoh - Sr. systems software engineer, Hughes STX, N0Y?? (in the mail)  +
+ USGS/EROS Data Center, Sioux Falls, SD, USA   57198     (605) 594-6830      +

+       "Welcome back my friends to the show that never ends!" EL&P             +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 
 
 

Newbie Scanner Antenna Questions

Post by David Hor » Sat, 07 Aug 1993 00:07:42


Quote:>DISCONE....
>attic.  The only catch was that his only goes from 144MHz to 1296MHz--not
>down to 30MHz, as both you and I need.
>If someone has/knows of plans for a discone that has the bandwidth of the
>Diamond D130J, I'd like to know about it--please.

Here's what I did with my Radio Shack Discone.  I unscrewed one of the
top elements and took it down to Home Depot (a hardware/home repair
outlet) and looked for copper tubing.  I found some that fit snugly
around the element (took minor resistance to push the element into the
tubing) and bought about 10 feet of the stuff.  I took it home and cut
it in half.  I put a five foot section around two opposite ends of the
discone's top elements and it made a significant difference on the low
bands.  The discone looks like it has a big dipole on the top now.  It
is horizontally polarized but that doesn't seem to be a drawback.  The
copper tubing bends rather easily but I have only had to straighten it
out once after a really bad storm.  You could use 4 foot sections for
better stability.  I read about the mod to put a vertical whip on the
top section but I had trouble getting it to work.  My solution may not
be the best but it is cheap, easy and it works!  I noticed no
difference in the SWR on the ham bands while transmitting so I can
still use the discone for 2m and 440 ham stuff.

Later,
David

 
 
 

Newbie Scanner Antenna Questions

Post by Jim Kearm » Sat, 07 Aug 1993 05:21:59





>|> >...
>|> >Can anyone give me advice on antennas.  What are the advantages and
>|> >disadvantages of the different types.  Can I build my own?  Any
>|> >problems putting the antenna in my attic?
>|> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^This sounds like a job for:
>|> DISCONE....
>|>...

The discone is a good choice for a scanner antenna.
If you're going to put the antenna in the attic,
you don't need the strength and foul-weather
resistance of a commercial discone. The fact that
a discone is a very broadband antenna implies it
should be easy to build one that works well.

The discone is so named because it combines a disk
with a cone (clever, eh?) Scanner-type discone
antennas have disks made of rod stock so ice and
snow don't build up as easily, but you can use solid
aluminum, copper or copperclad PC-board material
instead. All dimensions refer to the _lowest_ frequency
of interest.

Wavelength = 984/Freq (MHz)

Make the disk diameter about 0.7 wavelength.
The length of the cone side and its maximum diameter
(L) are about 0.25 wavelength. Make the disk diameter
about 0.7L.

The coax shield goes to the skirt and the center
conductor goes to the disk. The disk and skirt
should be separated by about an inch, but this
dimension, like the others, is not critical.
Spacing between the rods at the bottom should be
about 0.02 wavelength at the lowest frequency.

A discone is vertically polarized. Some commericial
units I've seen have staggered disk-rod and cone-rod
lengths, which is perhaps how they achieve the
extreme bandwidth they quote. You could make the
whole antenna out of 12-ga solid wire. Use a
lower frequency of 150 MHz for the short rods and
30 or 50 MHz for the long ones. The 30-MHz rods
will be about 7.5 feet long, but if your attic is
high enough, why not? Just hang the antenna from
a***hook. As I said, the dimensions are not
critical. Typical frequency range is 4:1, so you
will have to stagger the rod lengths to get the
over-10:1 coverage of the commercial antennas.

The discone has a low angle of radiation; the
higher you can install it the better. I can
envision one outside, covered with a plastic
garbage can for protection from the elements!

This information is from the _ARRL Antenna Book_.
Any _Antenna Book_ published in the last 20 years
has this info; the discone has been around for at
least 25 years!

Here are the dimensions for a 50-225 MHz discone; you can
extrapolate dimensions for higher bands. To cover 50-1300
MHz, I'd use these dimensions for half the rods, and cut
another set for 250 MHz (just divide these dimensions by
5). That should work fine.

        Disk Diameter           3.44'  
        Cone Length/Dia         4.92'
        Spacing                 0.39'

Good listening.

Jim

--

 
 
 

Newbie Scanner Antenna Questions

Post by (Mikey Likes » Sat, 07 Aug 1993 13:29:49

If only Grove would answer their e-mail.
I saw Tom's original post mentioning that they had an extended range
discone just after posting my statement that the Diamond seemed to be
the only one...I stand corrected.

Any idea who really makes Groves stuff?

And again, any specific plans aroung for the top element (b/t/w, I thought
a "top hat" was synonymous w/a capacitance hat, which is different than a
vertical element.  How would one add a hat to a disk?)
--
Michael Dahl/KC6UFR

 
 
 

Newbie Scanner Antenna Questions

Post by Brett Borows » Fri, 06 Aug 1993 23:00:03

[...]

Quote:>Grove and Universal catalogs both have discones with the vertical
>element for extended response down to 30 MHz.  (~$80)

>Radio Shack sells a good one to which the vertical can be added.  (~$60)

Does one just***the vertical on the bolt stick up out of the center of
the RS discone?  How long should the vertical be?  Is there any way to
improve the reception in 800mhz?  Inquiring minds what to know!

I've got the RS Discone sitting on the floor of my attic and it certainly
works well for VHF-Hi and UHF but my ruber duck cell-phone antenne is much
better at pulling in the NJ State Police's trunked system.  Would it be
worth the time trying to add that duckie to the discone?  Or should I stick
a straighten out paper click on as a vertical?

Is there a good book on this stuff?

Thanks!
Brett
--

 
 
 

Newbie Scanner Antenna Questions

Post by (Mikey Likes » Sat, 07 Aug 1993 16:00:35

Instead of a $60 R/S or $80 Grove (or the $76.95 Diamond), I did
mention previously that Radio Works lists one in their '91-'92
catalog for $29, and claims 100MHz to 2.5GHz...put a whip on the top
of that.

Also, I found the '73 article: Aug. '91, issue #371...it's the one
with the Poor Man's Packet cover story.  The article begins on pg. 24,
and is by Phil Salas/AD5X...144 to 1296MHz, for $19.39 in parts.

(1) 1" dia. brass washer
(1) 30" 1/8IP all-thread steel lamp pipe
1 light fixture canopy kit
6 brass 1/8IP nuts
1 plastic 4" dia. electrical box cover 10' #12 Cu wire
8 Cu-plated steel welding rods
(1) 12"x24"x1" piece of wood
(1) 4 1/2" sq. single-sided PC board
(6) 3/8" solder lugs (R/S # 64-3040 x 3)
5' RG-8M (that's 8X)

Basically, the threaded lamp rod gets the nuts run up it different lenghts to
retain the PC board disk/1" dia. brass washer at the top (and short radial
pieces of the welding rod soldered to the PC board), and the (long) welding rods
just below that (bent at the end where they get clamped between the nuts, so
they angle outwards).  The plastic round elect. box cover goes 1/2 way up the
lamp rod, so the Cu welding rods are stabilized (hot glue) against it.  The
coax goes up the inside of the lamp rod, and the whole thing rests on the 12"
x 24" x 1" piece of wood.
It seems trivial to attach a whip to the top, and one could vary the lenght of tthe rods to increse the bandwidth--as has been pointed-out previously.

Go to the library and check it out!
--
Michael/KC6UFR

 
 
 

Newbie Scanner Antenna Questions

Post by Tom Bod » Sat, 07 Aug 1993 21:52:56


|>...
|> And again, any specific plans aroung for the top element (b/t/w, I thought
|> a "top hat" was synonymous w/a capacitance hat, which is different than a
|> vertical element.  How would one add a hat to a disk?)
|> --
|> Michael Dahl/KC6UFR
|>

You are probably right - I couldn't think of anything else to call it and
that came to mind...

--

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Tom Bodoh - Sr. systems software engineer, Hughes STX, N0Y?? (in the mail)  +
+ USGS/EROS Data Center, Sioux Falls, SD, USA   57198     (605) 594-6830      +

+       "Welcome back my friends to the show that never ends!" EL&P             +
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 
 
 

Newbie Scanner Antenna Questions

Post by Withhe » Sat, 07 Aug 1993 22:36:02

Be forewarned that the following is from fuzzy memory, and should be
verified before any purchases are made.

I had a Radio Shack discone for a brief time a couple of years ago. As
has been noted here, it's short on the low end of the spectrum, but
there is a plastic cap over the top which, if removed, reveals some sort
of threaded base. It APPEARS that this unit was designed to have a whip
attached to the top of it in order to increase the range of the discone
on the lower end. It seemed reasonable to assume that the unit was
designed to accomodate the low frequency top portion as an option, but
for whatever reason RS chose not to market that option. I didn't have the
discone long, so I never got the chance to investigate it further, but
assuming the above is correct, what sort of whip would be required? Would it
simply be a matter of taking, say, a CB antenna whip and machining it to
match the top of the discone?

--

"An Irishman is never drunk as long as he can hold onto one blade of grass and
not fall off the face of the earth."