On 11/6/2023 11:24 AM, bitrex wrote:>> Isolation is 1/(reverse gain), and it’s a straight subtraction, so 60 >> dB is >> correct for the wrong reason. >> >> One way of keeping it straight is that an N-dB pad has 2N dB isolation. >> (Using the magnitude would predict an isolation of 0 dB.) The idea is to >> say how much a mismatch affects the input impedance. >> >> Cheers >> >> Phil Hobbs >> > > > > > > > Thank you, so just S21 - S12?To clarify I mean the log magnitudes here, as a VNA so conveniently can display for us
Minicircuits ZFL-500 directivity question
Started by ●November 4, 2023
Reply by ●November 6, 20232023-11-06
Reply by ●November 6, 20232023-11-06
bitrex <user@example.net> wrote:> On 11/6/2023 11:24 AM, bitrex wrote: > >>> One way of keeping it straight is that an N-dB pad has 2N dB isolation. >>> (Using the magnitude would predict an isolation of 0 dB.) The idea is to >>> say how much a mismatch affects the input impedance. >>> >>> Cheers >>> >>> Phil Hobbs >>> >> >>> >>> >> >> Thank you, so just S21 - S12? S21 for the ZFL-500 was about 20 dB and >> S21 -40 > > Sorry S12 was about -40, rather > >A reverse gain of-40 dB is an isolation of +40 dB, so the directivity is 40-20 = 20 dB. If you put a short or open on the output, it will reflect the full output power back into the output port. That’s 20 dB above the input power, so assuming a matched input and 40 dB isolation, you’d get an input return loss of 20 dB. That’s what the directivity expresses. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics
Reply by ●November 6, 20232023-11-06
On 11/6/2023 2:05 PM, Phil Hobbs wrote:> bitrex <user@example.net> wrote: >> On 11/6/2023 11:24 AM, bitrex wrote: >> >>>> One way of keeping it straight is that an N-dB pad has 2N dB isolation. >>>> (Using the magnitude would predict an isolation of 0 dB.) The idea is to >>>> say how much a mismatch affects the input impedance. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>>> >>> >>>> >>>> >>> >>> Thank you, so just S21 - S12? S21 for the ZFL-500 was about 20 dB and >>> S21 -40 >> >> Sorry S12 was about -40, rather >> >> > A reverse gain of-40 dB is an isolation of +40 dB, so the directivity is > 40-20 = 20 dB. > > If you put a short or open on the output, it will reflect the full output > power back into the output port. That’s 20 dB above the input power, so > assuming a matched input and 40 dB isolation, you’d get an input return > loss of 20 dB. That’s what the directivity expresses. > > Cheers > > Phil Hobbs >I see why JL loves his time domain. The 5080 is a nice instrument, it seems to boot to Windows 7. Crashes to Windows 7, too..
Reply by ●November 7, 20232023-11-07
On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote:> How is "directivity" defined for these Minicircuits gain blocks? > Datasheet here: > > <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf> > > Across the bandwidth of interest I'm measuring S21 as about 20-something > dB give or take a dB which seems fine, S12 is at -40. > > If "directivity" in this context is just S12 then that seems within spec > but if it's |S21 - S12| then something seems wrong with my setup and/or > the amp. > > Doing the measurements on a (unfortunately not my personal home-lab > machine!) Keysight 5080.They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted. Example: For "unit 1" and at 100 MHz, forward gain is +24.47859 dB. For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB. Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB) !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON) # Hz S dB R 50 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002
Reply by ●November 7, 20232023-11-07
On Tuesday, November 7, 2023 at 2:42:48 PM UTC-8, Simon S Aysdie wrote:> On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote: > > How is "directivity" defined for these Minicircuits gain blocks? > > Datasheet here: > > > > <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf> > > > > Across the bandwidth of interest I'm measuring S21 as about 20-something > > dB give or take a dB which seems fine, S12 is at -40. > > > > If "directivity" in this context is just S12 then that seems within spec > > but if it's |S21 - S12| then something seems wrong with my setup and/or > > the amp. > > > > Doing the measurements on a (unfortunately not my personal home-lab > > machine!) Keysight 5080. > They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted. > > Example: > For "unit 1" and at 100 MHz, forward gain is +24.47859 dB. > For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB. > > Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB) > > !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON) > # Hz S dB R 50 > 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002I should say: D = -|S12| (dB)
Reply by ●November 8, 20232023-11-08
On 11/7/2023 5:42 PM, Simon S Aysdie wrote:> On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote: >> How is "directivity" defined for these Minicircuits gain blocks? >> Datasheet here: >> >> <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf> >> >> Across the bandwidth of interest I'm measuring S21 as about 20-something >> dB give or take a dB which seems fine, S12 is at -40. >> >> If "directivity" in this context is just S12 then that seems within spec >> but if it's |S21 - S12| then something seems wrong with my setup and/or >> the amp. >> >> Doing the measurements on a (unfortunately not my personal home-lab >> machine!) Keysight 5080. > > They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted. > > Example: > For "unit 1" and at 100 MHz, forward gain is +24.47859 dB. > For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB. > > Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB) > > !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON) > # Hz S dB R 50 > 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002Thanks Simon, yes that seems right, this amp was bang on within spec otherwise so I'd have been surprised if it was way off there. They're nice lil modules, I didn't have this purpose in mind but I wonder if they make a LNA suitable to replace the shit ass front end on my DTV antenna, I live in a fringe area so reception varies by the day. and I'm in a condo so mounting stuff outdoors not really feasible
Reply by ●November 8, 20232023-11-08
On Wednesday, November 8, 2023 at 11:11:40 AM UTC-5, bitrex wrote:> On 11/7/2023 5:42 PM, Simon S Aysdie wrote: > > On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote: > >> How is "directivity" defined for these Minicircuits gain blocks? > >> Datasheet here: > >> > >> <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf> > >> > >> Across the bandwidth of interest I'm measuring S21 as about 20-something > >> dB give or take a dB which seems fine, S12 is at -40. > >> > >> If "directivity" in this context is just S12 then that seems within spec > >> but if it's |S21 - S12| then something seems wrong with my setup and/or > >> the amp. > >> > >> Doing the measurements on a (unfortunately not my personal home-lab > >> machine!) Keysight 5080. > > > > They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted. > > > > Example: > > For "unit 1" and at 100 MHz, forward gain is +24.47859 dB. > > For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB. > > > > Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB) > > > > !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON) > > # Hz S dB R 50 > > 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002 > Thanks Simon, yes that seems right, this amp was bang on within spec > otherwise so I'd have been surprised if it was way off there. > > They're nice lil modules, I didn't have this purpose in mind but I > wonder if they make a LNA suitable to replace the shit ass front end on > my DTV antenna, I live in a fringe area so reception varies by the day. > and I'm in a condo so mounting stuff outdoors not really feasibleYour reception is probably being degraded by suboptimal antenna pointing, the sun, and unpredictable multi-path signal impingement [ coastal is littoral causes no end of propagation anomalies ]. It doesn't cost the manufacturer anything to provide a high performance front end amplifier- all of which intended for satellite reception are LN-A's. The customers pay for everything, do you think it's wise then for them to provide junk performance parts making customers into ex-customers?
Reply by ●November 8, 20232023-11-08
On 11/8/2023 11:47 AM, Fred Bloggs wrote:> On Wednesday, November 8, 2023 at 11:11:40 AM UTC-5, bitrex wrote: >> On 11/7/2023 5:42 PM, Simon S Aysdie wrote: >>> On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote: >>>> How is "directivity" defined for these Minicircuits gain blocks? >>>> Datasheet here: >>>> >>>> <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf> >>>> >>>> Across the bandwidth of interest I'm measuring S21 as about 20-something >>>> dB give or take a dB which seems fine, S12 is at -40. >>>> >>>> If "directivity" in this context is just S12 then that seems within spec >>>> but if it's |S21 - S12| then something seems wrong with my setup and/or >>>> the amp. >>>> >>>> Doing the measurements on a (unfortunately not my personal home-lab >>>> machine!) Keysight 5080. >>> >>> They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted. >>> >>> Example: >>> For "unit 1" and at 100 MHz, forward gain is +24.47859 dB. >>> For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB. >>> >>> Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB) >>> >>> !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON) >>> # Hz S dB R 50 >>> 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002 >> Thanks Simon, yes that seems right, this amp was bang on within spec >> otherwise so I'd have been surprised if it was way off there. >> >> They're nice lil modules, I didn't have this purpose in mind but I >> wonder if they make a LNA suitable to replace the shit ass front end on >> my DTV antenna, I live in a fringe area so reception varies by the day. >> and I'm in a condo so mounting stuff outdoors not really feasible > > Your reception is probably being degraded by suboptimal antenna pointing, the sun, and unpredictable multi-path signal impingement [ coastal is littoral causes no end of propagation anomalies ]. It doesn't cost the manufacturer anything to provide a high performance front end amplifierIt doesn't? all of which intended for satellite reception are LN-A's. The customers pay for everything, do you think it's wise then for them to provide junk performance parts making customers into ex-customers? Could apply the same argument to many other industries...and conclude all products are high-quality because otherwise the manufacturer might lose customers. Hey, I have a cool idea, I'll see if I can put it on the 5080 next time I have a chance and see how it compares to a Minicircuits gain block for similar bandwidth, I think I can get a hold of one..
Reply by ●November 8, 20232023-11-08
On 2023-11-07 17:42, Simon S Aysdie wrote:> On Saturday, November 4, 2023 at 1:55:09 PM UTC-7, bitrex wrote: >> How is "directivity" defined for these Minicircuits gain blocks? >> Datasheet here: >> >> <https://www.mouser.com/datasheet/2/1030/ZFL_500_2b-3305829.pdf> >> >> Across the bandwidth of interest I'm measuring S21 as about 20-something >> dB give or take a dB which seems fine, S12 is at -40. >> >> If "directivity" in this context is just S12 then that seems within spec >> but if it's |S21 - S12| then something seems wrong with my setup and/or >> the amp. >> >> Doing the measurements on a (unfortunately not my personal home-lab >> machine!) Keysight 5080. > > They give S-params for 2 units. Conveniently, they are in dB/angle. The table just says 38 dB, more or less for directivity. By a quick look at the S-params and comparing to the datasheet table, I think they are just saying D = |S12| (dB), which you noted. > > Example: > For "unit 1" and at 100 MHz, forward gain is +24.47859 dB. > For "unit 1" and at 100 MHz, reverse gain is -38.36183 dB. > > Because the "directivity" looks to be about same as |S12|, it is safe to say they mean D = |S12| (dB) > > !Freq S11:SOLT2(ON) S21:SOLT2(ON) S12:SOLT2(ON) S22:SOLT2(ON) > # Hz S dB R 50 > 100000000 -3.318152e+001 -2.120138e+001 2.447859e+001 -1.975411e+001 -3.836183e+001 -1.134106e+001 -2.672768e+001 -1.570933e+002 >It isn't the absolute value in decibels. The directivity is just the magnitude of S21*S12. Otherwise you get the wrong answer for attenuators. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●November 8, 20232023-11-08
On Wed, 8 Nov 2023 11:11:31 -0500, bitrex <user@example.net> wrote:>They're nice lil modules, I didn't have this purpose in mind but I >wonder if they make a LNA suitable to replace the shit ass front end on >my DTV antenna, I live in a fringe area so reception varies by the day. >and I'm in a condo so mounting stuff outdoors not really feasibleThat ZFL-500 is not very suitable as antenna amplifier for DTV. First of all it is quite noisy, noise figure NF = 4.2 dB (typical). These days a good antenna amplifier the NF should be below 3 dB. That amplifier is specified only up to 500 MHz, thus most UHF channels are out of range. However, it might still work since the specs are good at 500 MHz, wonder why the specs ends at 500 MHz. An antenna amplifier should be installed _at_ the antenna, thus the cable between amplifier and DTV receiver can be long. You seem to suffer from tropospheric fading and the signal nulls can be quite deep and the signal is still momentary lost no matter what antenna amplifier you use. Only a proper outdoor antenna will really help.
