On Mar 20, 2022, at 06:52, Matt Huszagh via groups.io <huszaghmatt@...> wrote:

?It's worth adding that a DC block only provides some measure of safety. The ramp up voltage of a DC signal is an AC signal and can pass right through your series cap. If you look at DC blocking filter designs like the HP 3048A option K23, there's a limiter after the series cap. It seems like the "right" devices for this sort of thing are RF power limiters. Unfortunately, the cost of many of these devices new from reputable manufacturers probably matches or exceeds what many people paid for their second-hand spectrum analyzer. Maybe there are good second-hand market options, but I haven't looked into to it. If you want something to reliably protect a low frequency SA, that shouldn't be too hard to design and build. But, if you want to get the full 22 GHz range out of your 8566, I expect that wouldn't be so easy.

On Sun, Mar 20, 2022 at 08:59 AM, Lothar baier wrote:

Its not really a problem in real life since most DC blocks only have capacitors that are 100n or lower, the short current pulse doesn’t hurt anything!

It seems to me that saying "100n is small enough to protect the circuit" is not the answer, without stating how big the DC level is. Isn't it the ENERGY absorbed by the delicate components that is key?

A different variation on Protection: The AC line voltage here is routinely 125V. Some older equipment might be "stressed" by that. I use a buck transformer to bring it down to about 115V. The transformer, coincidentally, came from an HP spec-an that I disassembled for parts.

Pete

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

Those are transient limiters that are especially designed for this purpose , usually they only cover to 30 or 100MHz t match the frequency range of the LISN ( I only have seen the ones made by ETS that went to 100MHz not sure if they make higher frequency ones )

As far as the limiter itself concerns usually one attenuator of 3Db is used on the input followed by a diode limiter which is followed by another attenuator and then another ?limiter .

?

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

On Sunday 20 March 2022 02:02:21 pm greenboxmaven via groups.io wrote:

An older Uninterruptable Power Supply makes a very convenient way to 
reduce line voltage. Find one of the old "loaf of bread" sized units 
that uses the large 60 cycle transformer, rather than the newer ones 
that use a switching inverter. Remove everything except the transformer, 
fuse holder, outlets and switch. Use one half of the? primary winding 
along with the 120 volt secondary to make an autotranformer. It will 
drop 120 volts to about 109, which is much easier on older gear designed 
for 110 or 115 volts.

 ???? Bruce Gentry, KA2IVY

Interesting!  I happen to have a pile of those...

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

Tom,

?

That is also why MIL-STD-461 CE102 requires a 20dB Pad on the signal path from the LISN to the Receiver. They do not recommend a Limiter due to non-linearities that Lothar points out.

?

Limiters can really hurt the Noise Figure of a receiver input at well.

?

Ross

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

Tom,

?

That is also why MIL-STD-461 CE102 requires a 20dB Pad on the signal path from the LISN to the Receiver. They do not recommend a Limiter due to non-linearities that Lothar points out.

?

Limiters can really hurt the Noise Figure of a receiver input at well.

?

Ross

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

In my experience, non-military EMC, if the gadget you are testing can trigger the distortion of a limiter on a CE test, you are WAY above the limits you need to meet. It does make it harder to find the real offending frequencies, however. Then that 20 dB pad becomes beneficial as more than just a protective device..

?

Everything in front of the input screws up the noise figure; that’s just physics. Unless it’s a preamp, and then you have to watch for overload problems, much like the limiter effect.

?

?

?

Tom,

?

That is also why MIL-STD-461 CE102 requires a 20dB Pad on the signal path from the LISN to the Receiver. They do not recommend a Limiter due to non-linearities that Lothar points out.

?

Limiters can really hurt the Noise Figure of a receiver input at well.

?

Ross

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

What many people seem to forget is the fact that the non linear behavior of a limiter kicks in way before the limiter is actually “triggered” ?although the distortions are not as bad

?

?

Tom,

?

That is also why MIL-STD-461 CE102 requires a 20dB Pad on the signal path from the LISN to the Receiver. They do not recommend a Limiter due to non-linearities that Lothar points out.

?

Limiters can really hurt the Noise Figure of a receiver input at well.

?

Ross

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?

?

Lothar,

?

Correct. The same thing happens with Zeners below 6.2V and TVS Diodes (way too much Capacitance for RF Applications).

?

Look at the Breakover point of the RF Limiter (or TVS), it is a curve. Its Impedance changes below the breakover voltage as current flows through it and approaches the knee. If it is not specified, it can be obtained via a Curve Tracer or manually generated I-V Curves that you can produce with a simple Power Supply UUT and Resistance Standard or Resistance Decade.

?

Many Signal Integrity issues develop when they are not used properly and the curve is well understood.

?

Ross

?

?

What many people seem to forget is the fact that the non linear behavior of a limiter kicks in way before the limiter is actually “triggered” ?although the distortions are not as bad

?

?

Tom,

?

That is also why MIL-STD-461 CE102 requires a 20dB Pad on the signal path from the LISN to the Receiver. They do not recommend a Limiter due to non-linearities that Lothar points out.

?

Limiters can really hurt the Noise Figure of a receiver input at well.

?

Ross

?

?

Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

?

?

?

A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

?

?