RF mixer termination
 

Most mixers I've seen are not matched to 50+j0. They are simply terminated
in 50+j0. Is this the best or optimum termination or does it matter?

"John R. Strohm" wrote in message
...
"Alfred Lorona" wrote in message
...
Most mixers I've seen are not matched to 50+j0. They are simply
terminated
in 50+j0. Is this the best or optimum termination or does it matter?

There is no "best" or "optimum" termination, beyond the fact that you want
a
purely resistive termination. (DUH!). 50 ohms is just the standard value.

That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

Use other impedances at your own risk!

73, John - K6QQ

"John R. Strohm" wrote in message
...
"Alfred Lorona" wrote in message
...
Most mixers I've seen are not matched to 50+j0. They are simply
terminated
in 50+j0. Is this the best or optimum termination or does it matter?

There is no "best" or "optimum" termination, beyond the fact that you want
a
purely resistive termination. (DUH!). 50 ohms is just the standard value.

That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

Use other impedances at your own risk!

73, John - K6QQ

"John Moriarity" wrote in message
...

"John R. Strohm" wrote in message
...
"Alfred Lorona" wrote in message
...
Most mixers I've seen are not matched to 50+j0. They are simply
terminated
in 50+j0. Is this the best or optimum termination or does it matter?

There is no "best" or "optimum" termination, beyond the fact that you
want
a
purely resistive termination. (DUH!). 50 ohms is just the standard
value.

That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

Use other impedances at your own risk!

In the immortal words of Natasha the Sex Goddess: Well, DUH!

"John Moriarity" wrote in message
...

"John R. Strohm" wrote in message
...
"Alfred Lorona" wrote in message
...
Most mixers I've seen are not matched to 50+j0. They are simply
terminated
in 50+j0. Is this the best or optimum termination or does it matter?

There is no "best" or "optimum" termination, beyond the fact that you
want
a
purely resistive termination. (DUH!). 50 ohms is just the standard
value.

That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

Use other impedances at your own risk!

In the immortal words of Natasha the Sex Goddess: Well, DUH!

John R. Strohm wrote:
"John Moriarity" wrote in message
...

"John R. Strohm" wrote in message
...

"Alfred Lorona" wrote in message
...

Most mixers I've seen are not matched to 50+j0. They are simply

terminated

in 50+j0. Is this the best or optimum termination or does it matter?

There is no "best" or "optimum" termination, beyond the fact that you

want

a

purely resistive termination. (DUH!). 50 ohms is just the standard

value.

That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

Use other impedances at your own risk!


In the immortal words of Natasha the Sex Goddess: Well, DUH!



Where do I find this goddess?

John R. Strohm wrote:
"John Moriarity" wrote in message
...

"John R. Strohm" wrote in message
...

"Alfred Lorona" wrote in message
...

Most mixers I've seen are not matched to 50+j0. They are simply

terminated

in 50+j0. Is this the best or optimum termination or does it matter?

There is no "best" or "optimum" termination, beyond the fact that you

want

a

purely resistive termination. (DUH!). 50 ohms is just the standard

value.

That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

Use other impedances at your own risk!


In the immortal words of Natasha the Sex Goddess: Well, DUH!



Where do I find this goddess?

On Sun, 6 Jul 2003 21:44:22 -0700, "John Moriarity"
wrote:


That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

That may apply to most diode ring mixer, but this is not necessarily
true for other (active) mixers.

Paul OH3LWR

On Sun, 6 Jul 2003 21:44:22 -0700, "John Moriarity"
wrote:


That *may* be true, but most mixers are characterized
with 50 ohm (resistive) terminations at all ports.

That may apply to most diode ring mixer, but this is not necessarily
true for other (active) mixers.

Paul OH3LWR

"Alfred Lorona" wrote in message
...
Most mixers I've seen are not matched to 50+j0. They are simply terminated
in 50+j0. Is this the best or optimum termination or does it matter?

A commutating (or reversing switch) type mixer, such as a diode
ring mixer (DBM) will, ideally, present the same impedance at its input
as it is terminated in. This is because, in theory, the output is
always connected to the input, but the phase of the connection
reverses with time. Thus in a downconverting DBM, if the IF is
terminated in 50 ohms, the RF input will have a 50 ohm input
impedance. If the IF is terminated in 75 ohms, then the RF input
will have an impedance of 75 ohms.

In practical DBMs, transformers are used. These are optimized for
a particular impedance, so you will get best performance at the
specified impedance level.

The LO port input impedance has no particular value, being dependent
on drive level, diode turn-on voltage, etc. Typically, it is considerably
less than 50 ohms in a 50 ohm mixer. The manufacturer still advises
driving with a 50 ohm source so that the transformer will be optimally
terminated on at least the primary. I have driven DBM's with voltage
sources and current sources and they will often work OK that way.

Rick N6RK