Coax Quest. ?
 

Hello:

Don't have a good feeling for the significance of this:

For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver,
is a loss of, e.g., 2.5 db "meaningful" ?

Specifics would be 100 feet of RG 58 at 30 MHz

Or is it worth the extra $ to go to a less lossy coax (application would
always be for receive only)

BTW: R/S Coax a decent quality ?

Thanks,
B.

Coax Quest. ?
 

"Robert11" wrote in message
. ..
Hello:

Don't have a good feeling for the significance of this:

For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver,
is a loss of, e.g., 2.5 db "meaningful" ?

Specifics would be 100 feet of RG 58 at 30 MHz

Or is it worth the extra $ to go to a less lossy coax (application would
always be for receive only)

BTW: R/S Coax a decent quality ?

Thanks,
B.



The answer is, maybe. If the signal level of the stations you wish to hear
are strong, then -2.5db will not mean anything as receivers have a lot of
gain, but if the signals are weak then -2.5db can mean the difference
between hearing or not hearing a signal. Be aware that the loss figures for
coax are for a matched system, that is 50 ohms in/out. If the load is not 50
ohms, then the loss of the cable will be higher and the worse the miss match
the higher the excess loss will be. It can be allot. I've seen for severe
miss match excess loss of up to 20db.
As for R/S coax is not known for being of high quality nor is it consistent
in its quality.


--
John Passaneau, W3JXP
Penn State University

Coax Quest. ?
 

Robert/Bob

In a receive application it is only important that the signal you want
to hear exceeds the level of total system noise by a desired amount. In
your case atmospheric noise is likely to be far above that of whatever
the receiver front end contributes.

Having said that my HF/6m TXCVR has a preamp that can be used on 10M
with a slight useful effect. I'd suspect that this is a design problem
as the same model w/out 6m doesnt have it.

My answer is no, the 2.5dB can be ignored. You may want to consider
though how you should site/feed the antenna to obtain a good s/n ratio
from the desired signals.

I personally wouldnt touch RS coax but I have no evidence to back up my
thought that it is technically inferior. Just that they tend to buy
things cheap and there is a lot of rubbishy coax around. I might go to
the "Wireman" or direct to a well known manufacturers (Belden S&H etc)
retailer.

Cheers Bob VK2YQA

Robert11 wrote:

For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver,
is a loss of, e.g., 2.5 db "meaningful" ?

BTW: R/S Coax a decent quality ?

Coax Quest. ?
 

On Mon, 23 Jan 2006 08:32:40 -0500, "Robert11"
wrote:

Hello:

Don't have a good feeling for the significance of this:

For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver,
is a loss of, e.g., 2.5 db "meaningful" ?

Specifics would be 100 feet of RG 58 at 30 MHz

Or is it worth the extra $ to go to a less lossy coax (application would
always be for receive only)

BTW: R/S Coax a decent quality ?

The last time I bought Radio Shack coax cable, the shield was so
thinly populated with wire, it was almost nonexistant.

You might try some of your local computer stores that deal with
networking installations. They frequently carry good quality coax with
brand names like Beldon. (One of my local computer stores has Beldon
RG-58U at 22 cents a foot.)

Good mail order places for coax would include Davis RF, The Wireman,
RadioWorks, Amateur Electronic Supply, HRO, etc...

bob
k5qwg

Thanks,
B.

Coax Quest. ?
 

Robert11 wrote:
For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver, is a loss of, e.g., 2.5 db "meaningful" ?

Modern receivers have such a wide dynamic range that 2.5 dB
of loss on a received signal is usually of no consequence
at HF frequencies. Some hams don't even worry about that
amount of signal loss on transmit, ~ half an S-unit.
--
73, Cecil http://www.qsl.net/w5dxp

Coax Quest. ?
 

Bob Miller wrote:

(One of my local computer stores has Beldon
RG-58U at 22 cents a foot.)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you're going to search the internet, you have to spell it right:

Belden.

Bill, W6WRT

Coax Quest. ?
 

Robert11 wrote:

For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver, is a loss of, e.g., 2.5 db
"meaningful" ?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The answer depends on the noise figure of your receiver. Most modern
receivers have very low internal noise and will work fine under the
conditions you describe. Older receivers, especially tube sets,
generate so much internal noise that it may be stronger than the signal
you are trying to receive and the 2.5 dB loss will render the signal
inaudible.

In other words, it depends. :-)

Bill, W6WRT

Coax Quest. ?
 

At 30 MHz, you're right at the border between HF and VHF. Below about 30
MHz, atmospheric noise dominates, and reducing the coax loss will make
no difference at all in your ability to hear signals. Above about 30
MHz, receiver noise dominates, and reducing the coax loss 2.5 dB will
make an improvement, the amount depending on the relationship between
the receiver noise figure and the atmospheric noise. But the boundary is
fuzzy, so right at 30 MHz it's probably a toss.

But here's a very simple test you can do which will give you a
definitive answer: Tune the receiver to a frequency where there's no
signal, and disable the squelch if it has one so you can hear the noise.
Then disconnect the antenna from the receiver. (With some receivers you
might have to replace the antenna with a dummy load rather than just
disconnecting it, but that isn't usually necessary.) If the noise level
drops when you disconnect the antenna, reducing coax loss or otherwise
improving antenna efficiency won't make any difference in your ability
to hear signals. If the noise doesn't drop, then efficiency improvements
will improve your ability to hear signals.

Roy Lewallen, W7EL

Robert11 wrote:
Hello:

Don't have a good feeling for the significance of this:

For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver,
is a loss of, e.g., 2.5 db "meaningful" ?

Specifics would be 100 feet of RG 58 at 30 MHz

Or is it worth the extra $ to go to a less lossy coax (application would
always be for receive only)

BTW: R/S Coax a decent quality ?

Thanks,
B.

Coax Quest. ?
 

"Robert11" wrote in message
. ..
Hello:

Don't have a good feeling for the significance of this:

For a receive only application, using coax from the Balun of a simple
outside antenna to the receiver,
is a loss of, e.g., 2.5 db "meaningful" ?

Specifics would be 100 feet of RG 58 at 30 MHz

Or is it worth the extra $ to go to a less lossy coax (application would
always be for receive only)

BTW: R/S Coax a decent quality ?

Thanks,
B.

Don't get the R/S coax. If you can handle the aluminum wire shielding of
the cable TV RG-6 coax , use that. Less loss and the 70 ohm vrs the 50 ohm
is nothing to worry about. I usually use the RG-8X coax for frequencies
below 30 mhz instead of the rg-58. Not that more expensive.