I decided to share typical results for the various types so you can see typical response. The Crystek and TPI units were bought from Digikey and everything else was bought on Ebay.
I lack a spectrum analyser and tracking generator and network analyzer for doing this so I use my best fast reference level pulse generator and oscilloscope to test attenuators in the time domain by measuring their impulse response.
Thank you for your tests. Perhaps add in the price of the attenuators so we get an idea of how they compare for the price.
Mini Circuits VAT series of SMA 0-6 GHz attenuators - retail price of 11.95 USD each in small quantities.
Scale is 0.5 dB per division, 10,20,30 dB models measured.
I also checked my Bird 8322 200 watt 30 dB attenuator. It is rated to 500 MHz(within half a dB) tested to 2 GHz, I see it meets spec to 600 MHz.
I was able to buy the Mini Circuit attenuators I have locally for a few dollars each, they seem pretty fair for the price I guess.
I also checked my Bird 8322 200 watt 30 dB attenuator. It is rated to 500 MHz(within half a dB) tested to 2 GHz, I see it meets spec to 600 MHz.
I was able to buy the Mini Circuit attenuators I have locally for a few dollars each, they seem pretty fair for the price I guess.
I also checked my Bird 8322 200 watt 30 dB attenuator. It is rated to 500 MHz(within half a dB) tested to 2 GHz, I see it meets spec to 600 MHz.
I was able to buy the Mini Circuit attenuators I have locally for a few dollars each, they seem pretty fair for the price I guess.What VNA are you using?
In my working life we avoided buying attenuators over 20db because we often found the 30dB and greater units to have worse frequency response. This may not be true for all manufactures but it was our policy.
And for completeness some classic HP 8491A N attenuators, rated to 12.4 GHz and obviously stupid money.
I try and be patient and only buy >15GHz rated SMA attenuators and these can be found on ebay (used) quite cheaply if you can be patient and spot a bargain. A high frequency attenuator like this probably won't be very accurate (could be out by 0.3dB for example) but it will give a flat response. Usually better than +/-0.05dB over 6GHz for a 20dB attenuator for example.
QuoteAnd for completeness some classic HP 8491A N attenuators, rated to 12.4 GHz and obviously stupid money.
These should be really good up to 6GHz if they are healthy. I'd expect to see no wobbly ripple, just a smooth/gradual slope of maybe up to 0.1dB across LF through to 6GHz.
So I think they should be better (smoother?) than the response in your plots. Maybe it is your cables?
The scope input has 1MOhm || some Picofarads, at a PCB inside the unit.
Then, we have a piece of 50 line (from the socket at the scope to the input circuit at a PCB), ca 2cm
Then, we have the external BNC attenuator - another ca. 2 cm from match point to attenuator inside.
So, we have about 4cm of a 50 Ohm line after the attenuator inside to the 1MOhm scope input on a PCB.
Lets assume a velocity factor of 0.6 - so this piece has an electrical length of ca. 6.5cm, this is a quarter wavelength at around 1.2GHz. Result: Using a BNC 50 Ohm thru terminator for anything even close to a GHz is asking for trouble, regardless if the attenuator inside is properly built or not. I would say 500MHz is the absolute limit for something like this, if you would like to believe whats on your screen. In riseterm terms, this is about 700ps.
If your signals are faster, get a better scope that has a 50Ohm input.
This thread spurred me to check mine.
Specs for the Tek 1:1 and 10:1 attenuators in the Tek Attenuator pdf above.
A Pintek PL-50N 1:1 bought recently is the middle one and rated to 2 GHz.
This thread spurred me to check mine.
Specs for the Tek 1:1 and 10:1 attenuators in the Tek Attenuator pdf above.
A Pintek PL-50N 1:1 bought recently is the middle one and rated to 2 GHz.
I am surprised that Tektronix 10x (20dB) attenuator was that good but maybe I should not have been. Tektronix specified it as <1.1 VSWR at 1GHz and <1.2 VSWR at 2GHz. That feedthrough was specified at <1.1 VSWR at 250MHz and <1.2 VSWR at 500MHz. I have a pair of their lower frequency (<1.1 VSWR at 100MHz) 5W feedthroughs which were actually manufactured by someone else; ProbeMaster used to sell the exact same ones.
Their GR attenuators were specified up to 1GHz, their N attenuators up to 12GHz, and their SMA attenuators up to 18GHz.
The scope input has 1MOhm || some Picofarads, at a PCB inside the unit.
Then, we have a piece of 50 line (from the socket at the scope to the input circuit at a PCB), ca 2cm
Then, we have the external BNC attenuator - another ca. 2 cm from match point to attenuator inside.
So, we have about 4cm of a 50 Ohm line after the attenuator inside to the 1MOhm scope input on a PCB.
I have not examined any oscilloscopes which used a separate 50 ohm lead between the BNC and high impedance attenuator. They mostly either had a short flying lead which was usually part of a very small low value carbon composition resistor or the BNC was directly attached to the special printed circuit board with the high impedance attenuator.QuoteLets assume a velocity factor of 0.6 - so this piece has an electrical length of ca. 6.5cm, this is a quarter wavelength at around 1.2GHz. Result: Using a BNC 50 Ohm thru terminator for anything even close to a GHz is asking for trouble, regardless if the attenuator inside is properly built or not. I would say 500MHz is the absolute limit for something like this, if you would like to believe whats on your screen. In riseterm terms, this is about 700ps.
If your signals are faster, get a better scope that has a 50Ohm input.
The input capacitance of the high impedance buffer limits bandwidth up to about 500 MHz maximum. Oscilloscopes which are faster than this when the internal 50 ohm termination is used have a different arrangement where the input is switched by a microwave relay between the low impedance and high impedance circuit paths which duplicates how the old Tektronix 485 works; it is 250MHz in 1 megohm mode and 350MHz in 50 ohm mode and it has no internal feedthrough termination.
So the difference between using a good external feedthrough termination and the internal termination should be small. I cannot see any difference on my fastest high impedance oscilloscope but it is only 300MHz.
300MHz can be still OK. On a faster scope (Tek MSO4104, Keysight DSOS604, ...) differences are striking from a few 100MHz up.
This thread spurred me to check mine.
Specs for the Tek 1:1 and 10:1 attenuators in the Tek Attenuator pdf above.
A Pintek PL-50N 1:1 bought recently is the middle one and rated to 2 GHz.
I am surprised that Tektronix 10x (20dB) attenuator was that good but maybe I should not have been. Tektronix specified it as <1.1 VSWR at 1GHz and <1.2 VSWR at 2GHz. That feedthrough was specified at <1.1 VSWR at 250MHz and <1.2 VSWR at 500MHz. I have a pair of their lower frequency (<1.1 VSWR at 100MHz) 5W feedthroughs which were actually manufactured by someone else; ProbeMaster used to sell the exact same ones.
Their GR attenuators were specified up to 1GHz, their N attenuators up to 12GHz, and their SMA attenuators up to 18GHz.
Attenuators and terminators are completely different issues; Most attenuators go up to about 2GHz even when they are low quality. Shunting a coax by a 50 Ohm resistor, with the line reaching a few centimeters more and them terminated by 1MOhm and 10pF is a completely different story.