Discone antenna?
 

I have made up my mind to buy this antenna, but I have found a few different
models and don't know which to get. I am using a BC796D scanner. This will
be an outside antenna.

I have having trouble picking up the 850-869 range. my pro 2006 picks
up signals easily but the 43 will not even blink. Other freq are
working as far as i can tell.

Thanks in advance

Bo Harris

On Mon, 25 Oct 2004 16:41:27 -0400, "Brent"
wrote:

I have made up my mind to buy this antenna, but I have found a few different
models and don't know which to get. I am using a BC796D scanner. This will
be an outside antenna.


Diamond Discone

Minimum of 9913Flex cable for the coax

Get a GOOD quality coax and connectors like 9913Flex
as a minimum, LMR400 is preferable.

On Mon, 25 Oct 2004 16:00:21 -0700, Trooperdude
wrote:

On Mon, 25 Oct 2004 16:41:27 -0400, "Brent"
wrote:

I have made up my mind to buy this antenna, but I have found a few different
models and don't know which to get. I am using a BC796D scanner. This will
be an outside antenna.


Diamond Discone

Minimum of 9913Flex cable for the coax

Get a GOOD quality coax and connectors like 9913Flex
as a minimum, LMR400 is preferable.

I have a Pro-2052 w/ about 70ft of RG58 going up into the attic to hit
an RS discone. Here's what I will say, is that even with the really
crummy cable, reception is much better than it was with the other
antennas I tried, along with their shorter, higher quality cable runs.

These other antennas (not counting the crummy telescopic it came with
of course) are both mobiles. The first was a glass mount that I
bought two of, one for the car and one inside mounted to a little
stand I made. Reception was "ok".

The second is their wideband dual loaded magnetic mount, which was
quite a bit better than the other one, but still not great.

The #1 rule is of course height.. there is no substitute for it. Even
with the 70ft run -- I didn't want to drill holes in my ceiling, so it
goes across the roof to a closet, in through the trapdoor, then into
the middle of the attic -- I pick up much more than I did with the
other antenna. Partly design -- the discone is just better than any
kind of whip, but also because of the height difference of about 10-15
feet (and lack of wiring to interfere).

I can hear the ground control at the local airport now, which I was
never able to pick up before, and that's with an estimated loss of
about 10dB from the RG58.

The better cabling is an option (I'm looking for a good deal on some
9913 myself) but makes much more of a difference at high frequencies
than at lower ones. Even "crappy" RG8 only has a loss of around 5db @
400mhz for a 100ft run. 5db is enough that you'd notice, but it's
about the smallest amount that you *could* notice.

This is all out the window if you ever intend to transmit over that
same antenna. Get the best cabling you can and keep the run as short
as possible.

-Allen

On Tue, 26 Oct 2004 00:19:28 GMT, asym said
in rec.radio.scanner:

than at lower ones. Even "crappy" RG8 only has a loss of around 5db @
400mhz for a 100ft run. 5db is enough that you'd notice, but it's
about the smallest amount that you *could* notice.

3db is 50%, or one "S" unit - easy enough to notice. Actually, the
receiver capture ratio is the smallest amount you'll notice, so the
better the receiver, the smaller the change it takes to make a big
difference.

(If the capture ratio is, say, 2db, if the signal increases from the
noise level to 2db above the noise level, what you hear changes from
quite noisy to dead full quieting - very noticeable. If the capture
ratio of the receiver is under 1db, it takes less than 1db change to
make the above difference.)

BTW, the advantage of a discone is that it's a good match at just
about all the frequencies we're interested in. It's not much of an
antenna - it's more of a matching device between the end of the cable
and space.

On Tue, 26 Oct 2004 01:34:13 GMT, Never anonymous Bud
wrote:

Trying to steal the thunder from Arnold, asym on Tue, 26 Oct 2004 00:19:28 GMT spoke:

I have a Pro-2052 w/ about 70ft of RG58 going up into the attic to hit
an RS discone. Here's what I will say, is that even with the really
crummy cable, reception is much better than it was with the other
antennas I tried, along with their shorter, higher quality cable runs.

But the better coax will get you 3 to 4 times more signal into your radio.
Stuff you never even KNEW was there will come in clean.

Oh I don't doubt that, I was just making the point that height matters
a lot more. If I put the discone back down of the attic on a 20ft run
instead of a 70ft run, I lose reception on some things.. especially
the UHF and higher bands, where attenuation in the RG58 is terrible.

Obviously, height *and* good cable is the best. But if you're in a
situation where it's one or the other, go for height first, replace
the cable later if you can.


The better cabling is an option (I'm looking for a good deal on some
9913 myself)

LRM400 UltraFlex will make running the line much easier.
Yes, it costs about 30% more, but it's worth it.

davisrf (www.davisrf.com) has 9913 that they claim is 2.6dB per 100ft
at 400MHz.. while they say LMR400 is around 2.1.

But the real clincher is.. $0.46/ft for 9913, or $0.64/ft for 9913
FLEXI-4XL. For a difference of about 0.4db for the length I'm
running, again at ~400mhz.

Only quoting 400 all the time for two reasons.. one, it's in the
'middle' of the coverage of most broadband scanners/antenns.. second,
I transmit in that band, so it's a concern. ;)

On Tue, 26 Oct 2004 01:41:58 GMT, Al Klein wrote:

On Tue, 26 Oct 2004 00:19:28 GMT, asym said
in rec.radio.scanner:

than at lower ones. Even "crappy" RG8 only has a loss of around 5db @
400mhz for a 100ft run. 5db is enough that you'd notice, but it's
about the smallest amount that you *could* notice.

3db is 50%, or one "S" unit - easy enough to notice. Actually, the
receiver capture ratio is the smallest amount you'll notice, so the
better the receiver, the smaller the change it takes to make a big
difference.




(If the capture ratio is, say, 2db, if the signal increases from the
noise level to 2db above the noise level, what you hear changes from
quite noisy to dead full quieting - very noticeable. If the capture
ratio of the receiver is under 1db, it takes less than 1db change to
make the above difference.)

Yes, that's absolutely true. What I mean is basically, you're going
to be in the near field for a lot of transmission sources that create
a higher noise floor than is anywhere near optimal, most of the time..
so you'll never hear those weak stations. Low loss cable will not
help in this case, because the noise is attenuated as much as the
signal. If the S/N coming in is 3:1, then it will still be 3:1 after
the cable, it doesn't matter if the cable introduces 1dB or 10dB of
loss.

If your reciever sensitivity isn't up to snuff, then a lot of times it
doesn't matter how short or long your cable run is, or if it's high or
low quality.


BTW, the advantage of a discone is that it's a good match at just
about all the frequencies we're interested in. It's not much of an
antenna - it's more of a matching device between the end of the cable
and space.

Isn't that what an antenna is really all about anyway, any kind of
antenna? Some are designed to be directional and give you some amount
of gain, but in the end, they are there to capture waves -- to
interface the cable with space. ;)

Hi,

I'm no expert, but for whatever it's worth, I've tried
a R/S Disconne and also a Scantenna, side by side, in my attic.

The scantenna is better on all bands for my 780 Scanner.

Frankly, not by orders of magnitude better, but discernably "better".

Bob
---------------------
"asym" wrote in message
...
On Tue, 26 Oct 2004 01:41:58 GMT, Al Klein wrote:

On Tue, 26 Oct 2004 00:19:28 GMT, asym said
in rec.radio.scanner:

than at lower ones. Even "crappy" RG8 only has a loss of around 5db @
400mhz for a 100ft run. 5db is enough that you'd notice, but it's
about the smallest amount that you *could* notice.

3db is 50%, or one "S" unit - easy enough to notice. Actually, the
receiver capture ratio is the smallest amount you'll notice, so the
better the receiver, the smaller the change it takes to make a big
difference.




(If the capture ratio is, say, 2db, if the signal increases from the
noise level to 2db above the noise level, what you hear changes from
quite noisy to dead full quieting - very noticeable. If the capture
ratio of the receiver is under 1db, it takes less than 1db change to
make the above difference.)

Yes, that's absolutely true. What I mean is basically, you're going
to be in the near field for a lot of transmission sources that create
a higher noise floor than is anywhere near optimal, most of the time..
so you'll never hear those weak stations. Low loss cable will not
help in this case, because the noise is attenuated as much as the
signal. If the S/N coming in is 3:1, then it will still be 3:1 after
the cable, it doesn't matter if the cable introduces 1dB or 10dB of
loss.

If your reciever sensitivity isn't up to snuff, then a lot of times it
doesn't matter how short or long your cable run is, or if it's high or
low quality.


BTW, the advantage of a discone is that it's a good match at just
about all the frequencies we're interested in. It's not much of an
antenna - it's more of a matching device between the end of the cable
and space.

Isn't that what an antenna is really all about anyway, any kind of
antenna? Some are designed to be directional and give you some amount
of gain, but in the end, they are there to capture waves -- to
interface the cable with space. ;)

Al Klein schrieb:

3db is 50%, or one "S" unit - easy enough to notice. Actually, the
receiver capture ratio is the smallest amount you'll notice, so the
better the receiver, the smaller the change it takes to make a big
difference.



6 dB is the difference of one S-Unit. That's 25% of the Signal with one
more of S-Units.
For reception only purposes it's insiders knowledge to use _much_
cheaper lowloss tv-cable with 75 ohms runnig to a discone antenna. You
will hardly notice any loss for impedance mismatching as the impedance
curve of consumer grade scanners vary a lot from the 50 ohms.

Volker Tonn wrote:

Al Klein schrieb:

3db is 50%, or one "S" unit - easy enough to notice. Actually, the
receiver capture ratio is the smallest amount you'll notice, so the
better the receiver, the smaller the change it takes to make a big
difference.


6 dB is the difference of one S-Unit. That's 25% of the Signal with one
more of S-Units.
For reception only purposes it's insiders knowledge to use _much_
cheaper lowloss tv-cable with 75 ohms runnig to a discone antenna. You
will hardly notice any loss for impedance mismatching as the impedance
curve of consumer grade scanners vary a lot from the 50 ohms.

Use the very best 50 ohm coax you can afford.

dxAce
Michigan
USA