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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 |
"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 |
"Josh" wrote in message ... 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? http://www.amore.com/ Normally, I'd say "Google is your FRIEND", but the site Google has for her is gone. However, the other site, which the Google entry reminded me of, is still around. This site is actually for real, by the way. |
"Josh" wrote in message ... 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? http://www.amore.com/ Normally, I'd say "Google is your FRIEND", but the site Google has for her is gone. However, the other site, which the Google entry reminded me of, is still around. This site is actually for real, by the way. |
"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? Hi Alfred, a mixer is a three-port device. If I remember the theory, a three-port device can never be matched to the same characteristic impedance on all three ports. If two ports are matched, the third one is isolated, so that the network degenerates to a two-port device. Therefore a mixer with 50+0j ohm RF input cannot have 50+0j ohms neither at the LO input nor at the output. Some mismatch losses seem to be necessary with mixers, but they can be easily overcome by increasing the LO power and more amplification at the output. BR from Ivan |
"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? Hi Alfred, a mixer is a three-port device. If I remember the theory, a three-port device can never be matched to the same characteristic impedance on all three ports. If two ports are matched, the third one is isolated, so that the network degenerates to a two-port device. Therefore a mixer with 50+0j ohm RF input cannot have 50+0j ohms neither at the LO input nor at the output. Some mismatch losses seem to be necessary with mixers, but they can be easily overcome by increasing the LO power and more amplification at the output. BR from Ivan |
hello
all about theory of mixer on web site of minicircuits.com serge |
hello
all about theory of mixer on web site of minicircuits.com serge |
That might be true for lossless, linear networks (I honestly don't
know), but it's a simple manner to create a lossy three-port network that presents 50 ohms at all three ports. For example, a 16.67 ohm resistor from each port to a common point, or simply a 50 ohm resistor at each port with no internal connections between ports. A mixer is nonlinear besides having loss, so there's no good reason to believe that it conforms to rules that apply to lossless, linear networks. Roy Lewallen, W7EL OK1SIP wrote: "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? Hi Alfred, a mixer is a three-port device. If I remember the theory, a three-port device can never be matched to the same characteristic impedance on all three ports. If two ports are matched, the third one is isolated, so that the network degenerates to a two-port device. Therefore a mixer with 50+0j ohm RF input cannot have 50+0j ohms neither at the LO input nor at the output. Some mismatch losses seem to be necessary with mixers, but they can be easily overcome by increasing the LO power and more amplification at the output. BR from Ivan |
That might be true for lossless, linear networks (I honestly don't
know), but it's a simple manner to create a lossy three-port network that presents 50 ohms at all three ports. For example, a 16.67 ohm resistor from each port to a common point, or simply a 50 ohm resistor at each port with no internal connections between ports. A mixer is nonlinear besides having loss, so there's no good reason to believe that it conforms to rules that apply to lossless, linear networks. Roy Lewallen, W7EL OK1SIP wrote: "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? Hi Alfred, a mixer is a three-port device. If I remember the theory, a three-port device can never be matched to the same characteristic impedance on all three ports. If two ports are matched, the third one is isolated, so that the network degenerates to a two-port device. Therefore a mixer with 50+0j ohm RF input cannot have 50+0j ohms neither at the LO input nor at the output. Some mismatch losses seem to be necessary with mixers, but they can be easily overcome by increasing the LO power and more amplification at the output. BR from Ivan |
The post appears to have generated some interest. Specifically, how does the
match/mis-match, as the case may be, affect one of the (perhaps the) most important paramater which is the input 3rd order intermodulation distortion level? And what about loss? In other words, will a mixer (not limited to diode mixers) operate equally well into any termination as long as it is R+j0? AL |
The post appears to have generated some interest. Specifically, how does the
match/mis-match, as the case may be, affect one of the (perhaps the) most important paramater which is the input 3rd order intermodulation distortion level? And what about loss? In other words, will a mixer (not limited to diode mixers) operate equally well into any termination as long as it is R+j0? AL |
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