Hello,

Should have asked this also in my previous post re 50 or 75 ohm coax, but
I guess it is probably better to start a different thread.
New at this, so please pardon these very basic type of questions.

For a receiving only application, 30 MHz on down:
Putting up a new Inverted-L receiving antenna.

Radio, Balun, Lightning Arrestor use the 259 type of plug which I guess is
nominally for 50 ohm systems.

I can go with 75 ohm BNC connectors for the main coax run, but am pretty
well stuck with the
259 type for the already purchased units I noted above.

Intuitively, I guess I would like (all) 75 ohm connectors if I am using 75
ohm coax.

But, for 30 MHz and lower listening, would I even notice any difference,
probably ?

Is any received signal lost, or reflected back, at these 75-50 ohm junctions
?
If meaningful, any way around the problem ?

Thanks,
Bob

On Sat, 25 Feb 2006 15:33:11 -0500, "Robert11"
wrote:

Hello,

Should have asked this also in my previous post re 50 or 75 ohm coax, but
I guess it is probably better to start a different thread.
New at this, so please pardon these very basic type of questions.

For a receiving only application, 30 MHz on down:
Putting up a new Inverted-L receiving antenna.

Radio, Balun, Lightning Arrestor use the 259 type of plug which I guess is
nominally for 50 ohm systems.

I can go with 75 ohm BNC connectors for the main coax run, but am pretty
well stuck with the
259 type for the already purchased units I noted above.

Intuitively, I guess I would like (all) 75 ohm connectors if I am using 75
ohm coax.

But, for 30 MHz and lower listening, would I even notice any difference,
probably ?

Is any received signal lost, or reflected back, at these 75-50 ohm junctions
?
If meaningful, any way around the problem ?

Thanks,
Bob


No critical losses will be incurred by using UHF/BNC adaptors.
Question: Why not use F connectors?

In article ,
"Robert11" wrote:

Hello,

Should have asked this also in my previous post re 50 or 75 ohm coax,
but I guess it is probably better to start a different thread. New at
this, so please pardon these very basic type of questions.

For a receiving only application, 30 MHz on down: Putting up a new
Inverted-L receiving antenna.

Radio, Balun, Lightning Arrestor use the 259 type of plug which I
guess is nominally for 50 ohm systems.

I can go with 75 ohm BNC connectors for the main coax run, but am
pretty well stuck with the 259 type for the already purchased units I
noted above.

Intuitively, I guess I would like (all) 75 ohm connectors if I am
using 75 ohm coax.

But, for 30 MHz and lower listening, would I even notice any
difference, probably ?

Is any received signal lost, or reflected back, at these 75-50 ohm
junctions ? If meaningful, any way around the problem ?

Technically yes you will lose signal power in your antenna system with
each incorrect connector. WIth several wrong connectors the situation
gets complicated with multiple reflections in the antenna system.
Practically though the connectors have a very short electrical length at
30 MHz and lower so the effect of impedance mismatch will be small.

The best thing to do is use all the right stuff. Use the right cable and
connectors.

Using the wrong stuff has another complication in that you can have
mechanical trouble putting connectors on the coax. Mechanically things
may not fit well or at all. Connectors are designed with a size coax in
mind where 75 and 50 coax are not of the same dimensions.

BNC connectors are more commonly 50 ohms.

--
Telamon
Ventura, California

On Mon, 27 Feb 2006 13:58:18 GMT, "Dale Parfitt"
wrote:

.

BNC connectors are more commonly 50 ohms.

--
Telamon
Ventura, California

Just depends on what you specify when you buy the BNC connector. Just don't
try to mate a 75 Ohm BNC with a 50 Ohm BNC- same holds true for 75/50 type
N.
We recently built a high power 50--75 Ohm matching section for a CA
company. The unit had warnings that the output was 75 Ohm connector (their
choice). Got a call that they had destroyed the fingers on the 75 Ohm side
by screwing in a 50 Ohm mate. Very expensive mistake for them.

Dale W4OP


The pins are the same size in both flavors of BNCs.

http://sosnick.uchicago.edu/BNC_50_75.html

On Mon, 27 Feb 2006 14:10:32 GMT, David wrote:

On Mon, 27 Feb 2006 13:58:18 GMT, "Dale Parfitt"
wrote:

.

BNC connectors are more commonly 50 ohms.

--
Telamon
Ventura, California

Just depends on what you specify when you buy the BNC connector. Just don't
try to mate a 75 Ohm BNC with a 50 Ohm BNC- same holds true for 75/50 type
N.
We recently built a high power 50--75 Ohm matching section for a CA
company. The unit had warnings that the output was 75 Ohm connector (their
choice). Got a call that they had destroyed the fingers on the 75 Ohm side
by screwing in a 50 Ohm mate. Very expensive mistake for them.

Dale W4OP


The pins are the same size in both flavors of BNCs.

Type Ns are NOT interchangeable, but BNCs can be mixed up without
mechanical damage.

In article _zDMf.22547$pE4.21635@trnddc04,
"Dale Parfitt" wrote:

.

BNC connectors are more commonly 50 ohms.

--
Telamon
Ventura, California

Just depends on what you specify when you buy the BNC connector. Just don't
try to mate a 75 Ohm BNC with a 50 Ohm BNC- same holds true for 75/50 type
N.
We recently built a high power 50--75 Ohm matching section for a CA
company. The unit had warnings that the output was 75 Ohm connector (their
choice). Got a call that they had destroyed the fingers on the 75 Ohm side
by screwing in a 50 Ohm mate. Very expensive mistake for them.

Yep, you sure can't go mixing different impedance connectors. One
parameter that determines the impedance of the connector is the spacing
of the center to outer conductor so even if they look the same they
will not mate properly and stuff gets broken.

There are very small differences in contact dimensions you need to
measure with a micrometer in the microwave region so connectors don't
get busted and you need to use a torque wrench or the performance will
not be to specifications. Reflection measurements are very picky about
using the right torque on connectors.

It always pays to look closely at the connector before screwing
something together in case a connector has already been ruined as
another lesson learned in the lab.

--
Telamon
Ventura, California