Hello:

Will be putting up a new HF atnenna for Receive-Only, to be used from 30 MHz
on down

Trying to decide on a coax type for the radio to antenna run, about 150
feet.

As some will be buried in soil, want to have a PE jacket.

It appears that when factoring in the PE requirement, and certainly price, I
can
do better, apparently, by picking a 75 ohm coax than a 50 ohm one.

My receivers input is, of course, stamped 50 ohm.

In a practical sense, do you experts believe I would see any difference
between
50 or 75 ohm coax for a receive only situation at the 30 MHz and lower
listening freq's (150 foot coax run) ?

Thanks,
Bob

"Robert11" wrote in message
...
Hello:

Will be putting up a new HF atnenna for Receive-Only, to be used from 30
MHz
on down

Trying to decide on a coax type for the radio to antenna run, about 150
feet.

As some will be buried in soil, want to have a PE jacket.

It appears that when factoring in the PE requirement, and certainly price,
I
can
do better, apparently, by picking a 75 ohm coax than a 50 ohm one.

My receivers input is, of course, stamped 50 ohm.

In a practical sense, do you experts believe I would see any difference
between
50 or 75 ohm coax for a receive only situation at the 30 MHz and lower
listening freq's (150 foot coax run) ?


For receiving it will not make any differance. Even for transmitting it
will only mater if youare using a 50 ohm swr or power meter and want to read
it directly. Just use almost anyting but rg-58 or rg-59 is fine and those
are not too bad. If you could handle the connection of the noncopper
shield that most of the cable TV 70 ohm rg-6 has, that would probably be
your best bet. Don't even go to the real high grade of the quad shielded
stuff.

While the receiver says 50 ohms, it is doubtful that it is actually 50 ohms
except on a very few frequencies if even then.

Robert11 wrote:
It appears that when factoring in the PE requirement, and certainly price, I
can do better, apparently, by picking a 75 ohm coax than a 50 ohm one.

I use a lot of 75 ohm coax that I get for free from scrap
ends from the local cable TV company. Can't beat that price.
--
73, Cecil http://www.qsl.net/w5dxp

If you MUST use coax then prefer 75 ohms. Go for the greatest overall
75-ohm coaxial diameters. The greater the overall diameter the smaller
the attenuation in terms of dB per 100 feet.

There's no need to impedance match a 75ohm line to a 50-ohm receiver
for receiving purposes. The mismatch loss is quite small.

What matters is a severe mismatch between the antenna impedance and
the line impedance which will occur on some of the higher frequency
bands.
----
Reg.

On Sat, 25 Feb 2006 18:49:17 GMT, "Ralph Mowery"
wrote:


are not too bad. If you could handle the connection of the noncopper
shield that most of the cable TV 70 ohm rg-6 has, that would probably be
your best bet. Don't even go to the real high grade of the quad shielded
stuff.

In this part of the world, some types of quad shield, and even some
types of the dual sheild have one of the braids made from tinned
copper and are solderable, check out the specs or get a sample and
test it.

Additionally, crimp BNC(M) connectors, F(M) connectors and F(F)-BNC(M)
adapters are available.

Owen
--

Robert11 wrote:
. . .
In a practical sense, do you experts believe I would see any difference
between
50 or 75 ohm coax for a receive only situation at the 30 MHz and lower
listening freq's (150 foot coax run) ?

No.

Roy Lewallen, W7EL

I'd recommend a good grade RG-6 cable (70ohms) also. Regarding the
connectors, why not just use the standard TV F fittings all the way to the
Rx. You can put an F to whatever adapter on your Rx. TV cable and
fittings are not only cheap, but work quite well.



Ed K7AAT

On 25 Feb 2006 23:38:53 GMT, Ed
wrote:



I'd recommend a good grade RG-6 cable (70ohms) also. Regarding the
connectors, why not just use the standard TV F fittings all the way to the
Rx. You can put an F to whatever adapter on your Rx. TV cable and
fittings are not only cheap, but work quite well.

Agreed Ed.

I did see another post that suggested 50 ohms was better and to spend
the money.

The matched line loss of 150' of RG6 at 30MHz is 1.6dB. the MLL of
more expensive RG58C/U is 3.6dB, or the much more expensive RG213 is
1.6dB.

The antenna will not be matched over the whole range, so mismatch
losses will occur with both types of line, and there is no reason to
think that overall spending more money on RG213 with the attendent
loss of flexibility will actually be better.

In this rx only application, especially below 15MHz, even if the RG6
was a few dB worse than 50 ohm line, it would not be worth spending
the money on RG213.

Robert, if you want to bury the RG6, buy the standard grade and fit it
inside 13mm PE irrigation tube for better life.

Owen
--

Owen Duffy wrote:
. . .
In this rx only application, especially below 15MHz, even if the RG6
was a few dB worse than 50 ohm line, it would not be worth spending
the money on RG213.
. . .

I think Owen means, "even if the RG6 was a few dB *lossier*". In
receiving applications at HF, added loss (within reason) doesn't
translate to any reduction in signal/noise ratio. So one line can be
considerably lossier than another without making it even one little bit
worse in this application. There's no point in spending extra money on
line which won't make any improvement at all on your ability to receive
signals. It might, on the other hand, be worthwhile to pay extra for
line which will last longer or is more physically rugged. Or it might not.

Roy Lewallen, W7EL

On Sat, 25 Feb 2006 18:22:39 -0800, Roy Lewallen
wrote:

Owen Duffy wrote:
. . .
In this rx only application, especially below 15MHz, even if the RG6
was a few dB worse than 50 ohm line, it would not be worth spending
the money on RG213.
. . .

I think Owen means, "even if the RG6 was a few dB *lossier*". In
receiving applications at HF, added loss (within reason) doesn't
translate to any reduction in signal/noise ratio. So one line can be
considerably lossier than another without making it even one little bit
worse in this application. There's no point in spending extra money on
line which won't make any improvement at all on your ability to receive
signals. It might, on the other hand, be worthwhile to pay extra for
line which will last longer or is more physically rugged. Or it might not.

Quite.

The chart at http://www.vk1od.net/bpl/AreYouReady.htm shows that for a
good HF receiver, the ambient galactic noise is more than 10dB above
the rx noise floor. For an older receiver, the rx noise floor might be
10 to 15dB higher. The ambient noise due to man made and atmospheric
sources would be even higher than the galactic noise plotted in the
chart.

Owen
--