Problem with DISCONE antenna
Matthew Volkmer
Ive got a problem with my discone antenna.
It picks up VERY well on VHF freqs but not very good on UHF freqs.
(around 460mhz) Quite often my rubber ducky antenna is better!
Im using rg58u type coax (about 10 metres) Someone once told me that the
coax didnt have the best shielding or something like that but it was
tested with a multimeter and was ok.
Any ideas? Should I buy new coax?
Many Thanks
Matthew
PS I live in a big city so signal strength is not a problem.
Bill Cheek
mat...@adelaide.DIALix.oz.au (Matthew Volkmer) wrote:
>Ive got a problem with my discone antenna.
>
>It picks up VERY well on VHF freqs but not very good on UHF freqs.
>(around 460mhz) Quite often my rubber ducky antenna is better!
>
>Im using rg58u type coax (about 10 metres) Someone once told me that the
>coax didnt have the best shielding or something like that but it was
>tested with a multimeter and was ok.
>
>Any ideas? Should I buy new coax?
RG-58 is grossly inferior at frequencies above 20 MHz. It should never be
used for scanners, and especially for UHF reception.
RG-6 satellite cable is an excellent alternative. You'll need to put gold
plated "F" connectors on each end, and then at the scanner end, use an
F-to-BNC adapter to mate with the antenna jack. At the antenna end, get an
adapter for whatever it takes to mate the F connector to the antenna
connector.
Bill Cheek
COMMtronics Engineering
Bill Cheek
dd...@atl.mindspring.com wrote:
>>RG-58 is grossly inferior at frequencies above 20 MHz. It should never be
>>used for scanners, and especially for UHF reception.
>>
>>RG-6 satellite cable is an excellent alternative. You'll need to put gold
>>plated "F" connectors on each end, and then at the scanner end, use an
>>F-to-BNC adapter to mate with the antenna jack. At the antenna end, get an
>>adapter for whatever it takes to mate the F connector to the antenna
>>connector.
>>
>>Bill Cheek
>>COMMtronics Engineering
>I have RG-58 cable and am considering switching to RG-8 or RG-6 cable.
>Is it worth spending the money on RG-8?
No, no, no, for the luva Pete, no! RG-8 in most of its forms and styles, is
very lossy, too. Avoid it like the plague for VHF-UHF applications.
> Or would I notice a difference on switching to RG-6 on a 50' run?
You would note a difference, especially at UHF and up.
> The reason I haven't decided yet was RG-8's being somewhat inflexable.
It's flexible enough. That ain't the problem. RG-8 is lossy at VHF and UHF
frequencies.
> How does most people mount rg8 to handheld from antenna on roof?
There are a zillion adapters available for any need and purpose. For VHF
and UHF in RG-8 sized cables, it's best to install Type N connectors on each
end, and then get a set of adapters to fit whatever is at each end. BNC
adapters are common.
But there is only one RG-8 sized cable worthy of a scannists' attention,
and that's Belden 9913.....and heliax cable, of course. Otherwise, RG-6
satellite cable offers a lot of bang for the buck.
> Do most people run RG-8 from antenna on roof to a wall jack using
> BNC quick disconect male and then run a short piece of RG-59 from
> wall to handheld or base scanner?
A serious scannist won't do anything like that. No serious radioist would
do that. Instead you can get right-angle adapters and a host of things to
uncomplicate your situation. But never mix/match coax cables, and never
splice coax cable, either.
Bill Cheek
COMMtronics Engineering
dd...@atl.mindspring.com
bch...@cts.com (Bill Cheek) wrote:
>mat...@adelaide.DIALix.oz.au (Matthew Volkmer) wrote:
>
>>Ive got a problem with my discone antenna.
>>
>>It picks up VERY well on VHF freqs but not very good on UHF freqs.
>>(around 460mhz) Quite often my rubber ducky antenna is better!
>>
>>Im using rg58u type coax (about 10 metres) Someone once told me that the
>>coax didnt have the best shielding or something like that but it was
>>tested with a multimeter and was ok.
>>
>>Any ideas? Should I buy new coax?
>
>RG-58 is grossly inferior at frequencies above 20 MHz. It should never be
>used for scanners, and especially for UHF reception.
>
>RG-6 satellite cable is an excellent alternative. You'll need to put gold
>plated "F" connectors on each end, and then at the scanner end, use an
>F-to-BNC adapter to mate with the antenna jack. At the antenna end, get an
>adapter for whatever it takes to mate the F connector to the antenna
>connector.
>
>Bill Cheek
>COMMtronics Engineering
>
I have RG-58 cable and am considering switching to RG-8 or RG-6 cable.
Is it worth spending the money on RG-8? Or would I notice a difference
on switching to RG-6 on a 50' run? The reason I haven't decided yet
was RG-8's being somewhat inflexable. How does most people mount
rg8 to handheld from antenna on roof? Do most people run RG-8 from
W.R. Crabtree
It's not as bad as everyone is making it out to be.
YES they are better one's to be had.
First take advantage of what you have and mount it as high as you can.
DO NOT USE RG58 coax. The higher you go in freq. the better the coax you
need.
The biggest problem with the coax is what you need is to BIG and to
EXPENSIVE.
ie: 9913 coax.
I have found that a good quality RG6u quad shield cable is a good
compromise.
I use a Grove Pre-amp ($79.95) with the amp at the antenna end and the
control head at the radio.
I also have had very good luck with the Radio Shack ($29.95) in line amp
used for sat.dish installations.
The RS unit will pass thru any thing below 45o MHz aprox (I use this
mobile).
You can screw a low band stinger antenna on top of the RS DISCONE, it
should help.
Just changing your coax should make the biggest difference.
Don't worry about to impedance difference in the cable, from the receiver.
It won't any difference. It's so slight and your asking the receiver to
cover a extremely large freq.range. No antenna and cable would be in the
complete band spread.
Good Luck
dd...@atl.mindspring.com wrote in article
<32d62510...@news.atl.mindspring.com>...
Larry Levy
Hi, Matthew:
The problem is most likely the cable. RG-58 is very lossy cable at UHF
and 800 Mhz frequencies. Its ok for short cable runs, but there is
just too much signal loss for anything longer.
-Larry
mat...@adelaide.DIALix.oz.au (Matthew Volkmer) wrote:
>Ive got a problem with my discone antenna.
>
>It picks up VERY well on VHF freqs but not very good on UHF freqs.
>(around 460mhz) Quite often my rubber ducky antenna is better!
>
>Im using rg58u type coax (about 10 metres) Someone once told me that the
>coax didnt have the best shielding or something like that but it was
>tested with a multimeter and was ok.
>
>Any ideas? Should I buy new coax?
>
Norvin Adams III
I use about 70 feet of RG-8X. It is some kind of new cable that came out
awhile ago. I got mine at a CB shop. If I recall correctly, it does
everything RG-8 does which is very thick, but is thinner than 58. If I am
wrong don't shot me. I got my length for about $30. I highly recommend
it.
Norvin Adams III
Matthew Volkmer <mat...@adelaide.DIALix.oz.au> wrote in article
<5b480o$rak$1...@adelaide.DIALix.oz.au>...
Paul
Matthew Volkmer wrote:
>
> Ive got a problem with my discone antenna.
>
> It picks up VERY well on VHF freqs but not very good on UHF freqs.
> (around 460mhz) Quite often my rubber ducky antenna is better!
>
> Im using rg58u type coax (about 10 metres) Someone once told me that the
> coax didnt have the best shielding or something like that but it was
> tested with a multimeter and was ok.
>
> Any ideas? Should I buy new coax?
>
> Many Thanks
>
> Matthew
>
> PS I live in a big city so signal strength is not a problem.
coax is bad as the freq goes up the signal goes down.
Paul
Matthew Volkmer wrote:
>
> Ive got a problem with my discone antenna.
>
> It picks up VERY well on VHF freqs but not very good on UHF freqs.
> (around 460mhz) Quite often my rubber ducky antenna is better!
>
> Im using rg58u type coax (about 10 metres) Someone once told me that the
> coax didnt have the best shielding or something like that but it was
> tested with a multimeter and was ok.
>
> Any ideas? Should I buy new coax?
>
> Many Thanks
>
> Matthew
>
> PS I live in a big city so signal strength is not a problem.
Tony Langdon
It's 10 Jan 97 22:03:04,
We'll return to mat...@adelaide.DIALix.oz.au and All's
discussion of Problem with DISCONE antenna
ma> It picks up VERY well on VHF freqs but not very good on UHF freqs.
ma> (around 460mhz) Quite often my rubber ducky antenna is better!
ma> Im using rg58u type coax (about 10 metres) Someone once told me that
^^^^^
This is your problem. This stuff is about as good as wet string at UHF
(except for very short runs). Go out and buy (as a minimum) some 213
coax, or if you can afford it, 9913. :-)
ma> Any ideas? Should I buy new coax?
Definitely. You won't know yourself. :-)
213 should be fine for a strong signal area.
As a case study, I had a friend on UHF CB. He put up an antenna and ran
over 10m of RG-58 coax. His signal into the local repeater (15-20 km
away, and staring him in the face) was barely readable. Yet, when I
pulled up in the car in his driveway, the repeater would peg the needle
on my set. His radio checked out fine (power, etc).
At some stage, he changed to 213 coax, and put one hell of a signal into
that repeater. :)
As I said, spend some money and buy some coax. You won't know it's the
same old discone. :)
... TechnoBabble - Requires BS to understand!
--
| Fidonet: Tony Langdon 3:632/367.2
| Internet: tl...@freeway.DIALix.oz.au
|
| Freeway Internet Gateway, Melbourne, Australia. For information about
| our services and conditions of use, e-mail:
| in...@freeway.DIALix.oz.au, to receive a copy of the FAQ.
David Jerome
Paul <kell...@tiac.net> wrote in article <32D9A2...@tiac.net>...
> Matthew Volkmer wrote:
> >
> > Ive got a problem with my discone antenna.
> >
> > It picks up VERY well on VHF freqs but not very good on UHF freqs.
> > (around 460mhz) Quite often my rubber ducky antenna is better!
> >
> > Im using rg58u type coax (about 10 metres) Someone once told me that
the
> > coax didnt have the best shielding or something like that but it was
> > tested with a multimeter and was ok.
> >
> > Any ideas? Should I buy new coax?
> >
> > Many Thanks
> >
> > Matthew
> >
> > PS I live in a big city so signal strength is not a problem.
> Oh forgot to say you should use 9913 coax for tha !!!!!
>
Just a quick idea,
Try using thick ethernet co-ax for feeder cable. It's only 1/3 the cost of
9913, with better high frequency characteristics. (Using thin ethernet
cable instead of RG58U cable also works well - same cost savings for 6dB
less loss at 1000 MHz!)
BTW - use crimp type connectors rather than solder type, as the heat from
the soldering iron damages the foam dielectric and aviod walking over or
crimping the cable - that will ruin it!
Also, you may wish to make up a collet to slip over the braid, as both
ethernet cables are thinner than the RF equivalents.
This trick has worked well up in Queensland in a number of UHF repeaters
set up by my radio club.
Bill Cheek
"Norvin Adams III" <nad...@wincoinet.com> wrote:
>I use about 70 feet of RG-8X. It is some kind of new cable that came out
>awhile ago. I got mine at a CB shop. If I recall correctly, it does
>everything RG-8 does which is very thick, but is thinner than 58. If I am
>wrong don't shot me. I got my length for about $30. I highly recommend it.
No shooting, then, but the truth is that RG-8x is as old as the hills. It
isn't as good as RG-8, so since RG-8 is not a good choice for scanners,
RG-8x is even worse, though it may be a little better than RG-58. CB shops
are famous for reinventing the wheel every few years, and for perpetrating
some of the most goshawful fiction imagineable.
Bill Cheek
COMMtronics Engineering
fj...@enter.net
Bill, You say that RG-8 is not good for scanners, yet you recommend
RG-6. The loss for RG-6 is 2.2 dB @ 100 Mhz, and 4.4 dB @ 400 Mhz,
but the loss for RG-8 is 1.9 dB @ 100 Mhz and 4.1 dB @ 400Mhz. The
RG-6 is half the dia. of RG-8 and half the price, which is an
advantage, but as far as loss RG-8 is better. I got these figures
from the Radio Shack catalog. On another note in reinventing the
wheel Radio Shack sells RG-8/M and RG-8U as the same wire, is it
really. I went there to buy RG-8/M, but the wire I got was RG-8U.
The catalog number for the 8U was the same as the 8M.
Fred
James D. Cronin
In article <32d62510...@news.atl.mindspring.com>,
<dd...@atl.mindspring.com> wrote:
>
>I have RG-58 cable and am considering switching to RG-8 or RG-6 cable.
>Is it worth spending the money on RG-8? Or would I notice a difference
>on switching to RG-6 on a 50' run? The reason I haven't decided yet
>was RG-8's being somewhat inflexable. How does most people mount
>rg8 to handheld from antenna on roof? Do most people run RG-8 from
>antenna on roof to a wall jack using BNC quick disconect male and
>then run a short piece of RG-59 from wall to handheld or base scanner?
RG-8 is worth it; look for "foam" RG-8, which has a little less loss
at about the same price. There's also RG-213, a nicer version with
a better shield. (Some of the RG-8 has a very sparse braid.)
You could also go for 9913, the "poor man's hardline." The difference
in price from one to another is about the cost of lunch at a fast food
joint.
I use a discone with 9913 and a short length of RG-58 to a handheld
scanner. Works for me.
73..Jim N2VNO
--
James D. Cronin,
Northern Telecom
j...@cci.com
jdcr...@nt.com (new email address thanks to the idiots at BNR)
Joe Leikhim
Take apart the upper half of the discone and make sure that water has
not collected inside of the coaxial assembly. Mine did, so i took it
apart, dried it off and fitted o-rings to the threaded pieces. Worked
much better with out all the water. By the way, the discone should be an
open circuit if measured with an ohmmeter, if you see a short or leakage
like a capacitor then some water got in.
--
Joe Leikhim
Jlei...@nettally.com
"tv dinner by the pool,
i'm so glad i finished school" -F.Zappa 1967
"The Revolution will NOT be televised" -Gil Scott Heron
Jon Meeks
In article <32da81aa...@news.enter.net>, fj...@enter.net says...
>Bill, You say that RG-8 is not good for scanners, yet you recommend
>RG-6. The loss for RG-6 is 2.2 dB @ 100 Mhz, and 4.4 dB @ 400 Mhz,
>but the loss for RG-8 is 1.9 dB @ 100 Mhz and 4.1 dB @ 400Mhz. The
>RG-6 is half the dia. of RG-8 and half the price, which is an
>advantage, but as far as loss RG-8 is better. I got these figures
>from the Radio Shack catalog. On another note in reinventing the
>wheel Radio Shack sells RG-8/M and RG-8U as the same wire, is it
>really. I went there to buy RG-8/M, but the wire I got was RG-8U.
>The catalog number for the 8U was the same as the 8M.
> Fred
Fred,
The big problem I see with your data is that your loss data stops at 400MHz.
At 800MHz or above, RG6 knocks the socks off RG8 or RG8x or RG58. As the Freq.
goes up the loss does also, and at the higher freq's you need all the signal
you can get. Spend the little extra and get the RG6. But then if you really
use a Radio Shack catalog for your cable specs.... maybe the RG8 is good
enough...
--
****************** E-Mail to jme...@wwnet.com *******************
**** Then visit my home page at http://www.wwnet.com/~jmeeks ****
Nafana
In article <32d62510...@news.atl.mindspring.com>,
>Is it worth spending the money on RG-8? Or would I notice a difference
>on switching to RG-6 on a 50' run? The reason I haven't decided yet
>was RG-8's being somewhat inflexable. How does most people mount
>rg8 to handheld from antenna on roof? Do most people run RG-8 from
>antenna on roof to a wall jack using BNC quick disconect male and
>then run a short piece of RG-59 from wall to handheld or base scanner?
RG-8 isn't really that good at VHF-UHF- it was designed decades ago for
HF-band operation. I would suggest using RG-6- it has good VHF-UHF
performance, is readily available and relatively cheap. Don't worry about
the fact its 75-ohms- it will work just fine.
Leonard Weldon
Ref: The Discone/cable issue...
I currently am using the discone in the attic and have
about 4 cables (50) ft. coming down to my basement
complex. Having run experiments with various cables
over the years, I have found that performance is a bit
better on the RG-8 when running into both a HF receiver
and a scanner. Sitting within 3 ft of my receivers is a
full tower PC with a 17inch NEC monitor...the coax
coming in, runs behind the monitor and very close to the
computer. Experimenting with some very cheap 75 ohm
stuff and some RG-6, I found that the RG-8 is better
shielded and is much quieter than the other cables in
terms of shielding out TV radiation interference, computer
monitor interference, etc. The NEC monitors, particularly
the "E"series are shielded extremely well...they exceed
the Government requirements in this regard. But, you'll
pay for it!
When you switch to the other cables on the HF receiver,
the local interference is very noticeable...one goes from
a fairly quiet background of atmospheric hiss and noise
to the obvious local radiation! The signal/noise ratio is
notably worse! I also note that I can back off the squelch
on my RS JRE 2035 scanner a bit...more signals are
present..I think a good broadband pre-amp at the
antenna is in order next! The quiet RG-8 would carry
more of the signal down to the receiver. Keep in
mind that a lower noise ratio is equivalent to an increase
in signal! Cable sensitivity looks better!
The bottom line is that the top of the line RG-8 presents
a quieter signal to the receivers...it is the best that I have
tried to this point...I am aware there is a very expensive
cable (can't remember the number) that has been discussed...
I'll try it a bit later...but at the present, I have RG-8 connected
to both the scanner and to a "sloper" antenna for HF and
the R-5000. I have a decent ground system in place also!
I think there are some double shielded varieties of RG-8 out
there...I think the older cable, that I have running to my HF
receiver is that type. All of the cable I have tried are by Belden.
I also have a belief that some of the less well shielded cable
also acts as a vertical antenna and adds to the signal along
with the noise. For those that are fighting the local noise
issue (computer, TV), there is an excellent device by
JPS, model ANC-4,..this is for the HF bands only..it works..
knocks out line noise very well...works on the RF level...
it picks up the local noise on a vertical antenna mounted
on the ANC-4 and subtracts this noise from the RF that
gets to your receiver..very sophisticated instrument!
Enough of this ramblin' on...hope this helps some of you out
there...
Leonard...
P.S. I just looked at one of the cables still coming down and it
is an old 72ohm cable TV piece. Junky stuff.
__________________________________________________________
On 16 Jan 1997 07:33:53 GMT, naf...@peganet.com (Nafana) wrote:
:In article <32d62510...@news.atl.mindspring.com>,
:
Brett Duane
In article <5bkll2$g...@andromeda.peganet.net>, naf...@peganet.com says...
>
>In article <32d62510...@news.atl.mindspring.com>,
>>I have RG-58 cable and am considering switching to RG-8 or RG-6 cable.
>>Is it worth spending the money on RG-8? Or would I notice a difference
>>on switching to RG-6 on a 50' run? The reason I haven't decided yet
>>was RG-8's being somewhat inflexable. How does most people mount
>>rg8 to handheld from antenna on roof? Do most people run RG-8 from
>>antenna on roof to a wall jack using BNC quick disconect male and
>>then run a short piece of RG-59 from wall to handheld or base scanner?
>
> RG-8 isn't really that good at VHF-UHF- it was designed decades ago for
>HF-band operation. I would suggest using RG-6- it has good VHF-UHF
>performance, is readily available and relatively cheap. Don't worry
about
>the fact its 75-ohms- it will work just fine.
Sure, it'll work fine, IF you can live with the signal attentuation
caused by the 50/75 ohm mis-match between the antenna and coax, and again
from the coax to the radio. Is can be about the loss as RG-8 (which is 50
ohms.)
Better yet, use RG-213 or 9913.
And get rid of those "UHF" connectors. They also attentuate greatly above
30MHz. (They were invented in a time when 50MHz was considered about the
top of the usable spectrum.) Use BNC or N connectors.
--
These are just a few of my thoughts, but you can have them for only $3.95
----
Brett KA7CGB
E-mail: dd3...@goodnet.com
Home Page: http://www.goodnet.com/~dd37666
Nafana
In article <5br06j$r...@news.goodnet.com>, dd3...@goodnet.com says...
>
>In article <5bkll2$g...@andromeda.peganet.net>, naf...@peganet.com says...
>>
>>In article <32d62510...@news.atl.mindspring.com>,
>>>I have RG-58 cable and am considering switching to RG-8 or RG-6 cable.
>>>Is it worth spending the money on RG-8? Or would I notice a difference
>>>on switching to RG-6 on a 50' run? The reason I haven't decided yet
>>>was RG-8's being somewhat inflexable. How does most people mount
>>>rg8 to handheld from antenna on roof? Do most people run RG-8 from
>>>antenna on roof to a wall jack using BNC quick disconect male and
>>>then run a short piece of RG-59 from wall to handheld or base scanner?
>>
>> RG-8 isn't really that good at VHF-UHF- it was designed decades ago for
>>HF-band operation. I would suggest using RG-6- it has good VHF-UHF
>
>Sure, it'll work fine, IF you can live with the signal attentuation
>caused by the 50/75 ohm mis-match between the antenna and coax, and again
>from the coax to the radio. Is can be about the loss as RG-8 (which is 50
>ohms.)
>
>Better yet, use RG-213 or 9913.
>
>And get rid of those "UHF" connectors. They also attentuate greatly above
>30MHz. (They were invented in a time when 50MHz was considered about the
>top of the usable spectrum.) Use BNC or N connectors.
>
>
Well 9913 is fine- in fact it is what I use- but it is relatively expensive
and if he thought RG-8 was too stiff- he would surely think that of 9913! As
for the impedance mis-match- scanner-antennas operate over too wide a
frequency ranges to stay a flat 50-ohms anyway. Nor are scanners going to be
exactly 50-ohms at all frequencies. In-short- the loss caused by impedance
mis-match in scanner applications is trivial- and far less than that caused
by poor coax, or too many connectors.
An additional advantage of using RG6 is the large selection of inexpensive
switches, splitters and amps available for use with "F"-connectors.
-Naf
Per H. Nielsen
dd3...@goodnet.com (Brett Duane) writes:
>>the fact its 75-ohms- it will work just fine.
>Sure, it'll work fine, IF you can live with the signal attentuation
>caused by the 50/75 ohm mis-match between the antenna and coax, and again
>from the coax to the radio. Is can be about the loss as RG-8 (which is 50
>ohms.)
If we are speaking of discone antennas don't worry about cable impedance.
The impedance of discones vary with frequency and is nothing near
50 ohms over the entire range.
--
Per H. Nielsen Telephone: Int +45 42 84 50 11
Software Division Fax: Int +45 42 84 52 20
Dansk Data Elektronik A/S, Herlev, Denmark E-mail: p...@dde.dk
My Danish Scanner Pages: http://www.geocities.com/SiliconValley/9880
jfo...@ionet.net
Does not this only work when you have an impedeance mismatch? If the
VSWR is low (<1.3:1 +/-?) there is no reason to use antenna feed lines
that are in multiples of half wave lengths, besides is not this
method normally used in Tx work not in Rx work? If the VSWR is really
that bad you need to get a better antenna system.
jim