mixer isolation value comes negative but papers shows it positive

[jignesh_prajapati]

hi
i have designed down conversion mixer it isolation shows negative results(between -65 to -70)
many papers i have seen they consider it as positive means 65db isolation here one paper image link is attached
https://obrazki.elektroda.pl/2197191600_1431599923.jpg


please help

 

[vfone]

Just change the (-) sign with (+) and you will be fine.
Is about the meaning from which side you look to this isolation value in dB.

 

[D.A.(Tony)Stewart]

Isolation and attenuation implies negative levels.

Positive levels imply gain.

- computer programmers never lie so they give polarity as programmed.

 

[mtwieg]

Attenuation and isolation are basically the inverse of gain. But in the real world, simply using one of those two terms is going to imply that the power gain is negative. So if someone gives you an attenuator labelled -6dB and another labelled 6dB, you can be confident that neither has an amplifier hidden inside.

 

[vfone]

Computer programmers or computer programs, never lie?

Another example, engineers mention that a passive mixer have a loss of about 6dB, and sometimes that the same mixer has a gain of -6dB.
Even some RF instruments use different sign for set the external attenuation in dB. For example some Agilent (Keysight) use a positive number, when some R&S use a negative number, but their meaning is the same.
If you know for what you are looking for, never get confused, but I agree we should keep a kind of rule.

 

[jignesh_prajapati]

thank u very much for ur reply

i need more explaination
how can i explain it in my presentation because in graph it is showing negative

 

[mtwieg]

Just say isolation and flip the graph of gain to use positive numbers. It's entirely valid.

 

[volker@muehlhaus]

because in graph it is showing negative

For the graph that you showed in post #1, we understand what it means but technically it is wrong. The y axis shows transmission (-30dB), not isolation.

Transmission -30dB means the same as +30dB isolation. If we want to plot isolation, we must have positive numbers to be technically correct.