I have noticed the same issue. Five years ago those things seemed really common, now it took looking on eBay for a couple of months just to find a single set of four. That said, I am sure they are still out there - you just have to wait a bit sometimes for a set to come along.
-Matthew
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Re: HP 3456A Problem Solved
Larry, I had a similar symptom with my 3456A.? It was intermittent when I got it, but since it worked a good part of the time I decided to keep it and live with it.
After a while the intermittent stopped and it's been perfect ever since.? I decided it must be that it hadn't been used enough and some oxide built up in critical places.
After reading your post, I know what to look for in case it acts up again.
Bob
On Saturday, March 7, 2020, 08:13:44 PM PST, n4buq <n4buq@...> wrote:
A few weeks ago, I reported a problem with my 3456A where it would fail at startup with "--------" on the readout and fail Test 3.? I reseated one of the microprocessors and the problem seemed to go away.? Since Service Note 3456A-13A states to discard the chip sockets for all three microprocessors and solder them to the board, I figured the problem was in those red chip sockets and decided instead to replace them with good quality machined sockets as I believe others have done as well.
Unfortunately, after replacing all three sockets, the problem persisted so I started down the troubleshooting steps in the manual and one of the very first things it says to check is +5V on U13 (one of the microprocessors).? I was surprised to find that to be at 4.7V or, possibly, a few hundredths under that.? Since I had replaced all the electrolytics in the power supply, an off voltage like that was something I did not expect at all.? Checking that rail at the power supply board, though, showed it to be around 5.1V.
Knowing that Service Note 3456A-14A addresses an issue with faulty grounds (via some riveted ground lugs), I decided to ensure the In Guard board was properly grounded so I jumpered one of the GND test points on that board to one of the GND pins on the power supply board and the meter immediately started working.? If I remove the jumper, the meter stops in its tracks and restarting it produces that same "--------" and failed Test 3.
I can detect about 0.5 ohms from the pin that connects to the power supply and the pin that connects GND to the In Guard board and apparently that's just enough resistance to drop the voltage low enough to cause the processor to stop so better grounding is in order.
While I'll probably go with the Service Note's recommendation and replace the rivets with #2-56 screws, nuts, and lock washers, I'm wondering why it might not be a better plan to simply route ground wiring from pin to pin as needed.? I see where that was done from the factory from one or two other pins and it would seem that a separate, soldered wire might be better off since tiny screws might tend to need cinching up from time to time to ensure they're still tight.
Has anyone here performed the rivet replacement?? I suppose I'll stick with that since it's recommended (and will include a drop of DeoxIT under each lug as well) but was just curious as to whether a separate wire would be a better plan.
Thanks,
Barry - N4BUQ
|
A few weeks ago, I reported a problem with my 3456A where it would fail at startup with "--------" on the readout and fail Test 3. I reseated one of the microprocessors and the problem seemed to go away. Since Service Note 3456A-13A states to discard the chip sockets for all three microprocessors and solder them to the board, I figured the problem was in those red chip sockets and decided instead to replace them with good quality machined sockets as I believe others have done as well.
Unfortunately, after replacing all three sockets, the problem persisted so I started down the troubleshooting steps in the manual and one of the very first things it says to check is +5V on U13 (one of the microprocessors). I was surprised to find that to be at 4.7V or, possibly, a few hundredths under that. Since I had replaced all the electrolytics in the power supply, an off voltage like that was something I did not expect at all. Checking that rail at the power supply board, though, showed it to be around 5.1V.
Knowing that Service Note 3456A-14A addresses an issue with faulty grounds (via some riveted ground lugs), I decided to ensure the In Guard board was properly grounded so I jumpered one of the GND test points on that board to one of the GND pins on the power supply board and the meter immediately started working. If I remove the jumper, the meter stops in its tracks and restarting it produces that same "--------" and failed Test 3.
I can detect about 0.5 ohms from the pin that connects to the power supply and the pin that connects GND to the In Guard board and apparently that's just enough resistance to drop the voltage low enough to cause the processor to stop so better grounding is in order.
While I'll probably go with the Service Note's recommendation and replace the rivets with #2-56 screws, nuts, and lock washers, I'm wondering why it might not be a better plan to simply route ground wiring from pin to pin as needed. I see where that was done from the factory from one or two other pins and it would seem that a separate, soldered wire might be better off since tiny screws might tend to need cinching up from time to time to ensure they're still tight.
Has anyone here performed the rivet replacement? I suppose I'll stick with that since it's recommended (and will include a drop of DeoxIT under each lug as well) but was just curious as to whether a separate wire would be a better plan.
Thanks,
Barry - N4BUQ
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Re: HP 8591 external reference connector (1250-1499)
Daun is right a bnc to bnc will work fine. Do it all the time. Any reasonable cable length will work. Have fun Regards Paul WB8TSL
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Re: HP 8591 external reference connector (1250-1499)
All - Thanks. I am glad to hear that a regular piece of short quality BNC (HP 10502A or similar I presume) will work fine. I figured that the special form factor is just for mechanical convenience, but thought I would ask.
Daniel - I sent you email.
-Matthew
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Re: Testing dummy loads with a VNA
Leave it to the ME to mess up the Ohm¡¯s law :) I meant of course F=ma vs I=V/R, and mass is then the equivalent of conductance, not resistance. D¡¯oh. - Kuba
toggle quoted message
Show quoted text
7 mars 2020 kl. 10:29 em skrev Kuba Ober <kuba@...>:
?I can chime in as a ME wearing an EE hat :) I see S11 measurement as essentially a shaker table measurement where you are not allowed to touch anything but the interface plane. Imagine a shaker and a load cell + an accelerometer between the shaker and the DUT. Or think of holding a short slinky hanging down from your arm. Close your eyes - you can only feel the interface plane. Shake it in various ways and you get the slinky¡¯s S11 response.
Then stick a load cell with a test mass and another accelerometer stuck to it on the far end, and you get S12. Swap the ends and you can measure S22 and S21.
In one ¡°interpretation¡±, the load cell measures the mechanical equivalent of current. The accelerometer measures the mechanical equivalent of voltage. In such interpretation (one of many), mass is the equivalent of resistance (I=V*R vs F=a*m). If we let acceleration represent a higher derivative of voltage, you can also find mechanical equivalents for capacitance and resistance. If we let the velocity be the equivalent of voltage, then mechanical damping becomes equivalent to real impedance, and inertia is equivalent to imaginary impedance. And so on, and pardon for mathematical mistakes here. But the gist of it is: you can certainly derive mechanical analogues of electrical circuits. The reverse of it was an actual job description not too long ago, when analog computers simulated mechanical systems and were used to model such.
In an S-parameter test set - and anyone actually knowing what they talk about please correct me - directional couplers and RF switches do the job of separating the energy flow out of a port from the flow into the port.
Circulators are a particularly clever kind of a directional coupler that¡¯s connected back to itself (at least I think of them that way) - the energy can make it all the way back to the 1st port if the ports on the way reflect it ¡°back¡± - back into the respective ports, but forward in the circulator (there¡¯s an arrow on it that shows which way is ¡°forward¡±, at least on the few I got). A circulator is the RF equivalent of a lazy Susan :)
The ¡°problem¡± with bare VNAs is that the S-parameter test set is a separate device, and a costly one from what I gather, yet one without which the capability of the VNA is quite untapped. The ¡°bare¡± VNA is the RF power source and one or more fancy vector voltmeters. A test set is what connects those up in a circuit that allows a particular kind of very useful measurements (one- and two-port S-parameter measurements). It¡¯s what lets you use those load cells and accelerometers for something useful :)
Best not let the ME ramble too much, though.
Cheers, Kuba
7 mars 2020 kl. 7:41 em skrev Dave McGuire <mcguire@...>:
?On 3/7/20 6:43 PM, David C wrote:
dummy load is a termination with only an input!
If its a parallel connection, yes. Why not a series connection?
VNAs are intended to do "thru' measurments on systems of a
characteristic impedaance (probably 50 ohms) Uhhh...wha?? No. That's one thing that they can do, but the
assertion that they are "intended" to only do thru measurements is
false. Very, very false.
Some are able to do "single port' i.e. connect the load across the TX
port and read that. I've never seen a VNA that is unable to do "single port". And from
where I'm sitting right now I can throw a wad of gum at five different VNAs.
Thats not actually
a 'network analysis' because a dummy load is not exactly a network (read
about Fosters networks). In fact is *is* exactly a network, and performing an S11 analysis on
one is in fact, by definition, network analysis.
Wow. Please read up on what a network is and what VNAs do.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
|
Re: Testing dummy loads with a VNA
I can chime in as a ME wearing an EE hat :) I see S11 measurement as essentially a shaker table measurement where you are not allowed to touch anything but the interface plane. Imagine a shaker and a load cell + an accelerometer between the shaker and the DUT. Or think of holding a short slinky hanging down from your arm. Close your eyes - you can only feel the interface plane. Shake it in various ways and you get the slinky¡¯s S11 response.
Then stick a load cell with a test mass and another accelerometer stuck to it on the far end, and you get S12. Swap the ends and you can measure S22 and S21.
In one ¡°interpretation¡±, the load cell measures the mechanical equivalent of current. The accelerometer measures the mechanical equivalent of voltage. In such interpretation (one of many), mass is the equivalent of resistance (I=V*R vs F=a*m). If we let acceleration represent a higher derivative of voltage, you can also find mechanical equivalents for capacitance and resistance. If we let the velocity be the equivalent of voltage, then mechanical damping becomes equivalent to real impedance, and inertia is equivalent to imaginary impedance. And so on, and pardon for mathematical mistakes here. But the gist of it is: you can certainly derive mechanical analogues of electrical circuits. The reverse of it was an actual job description not too long ago, when analog computers simulated mechanical systems and were used to model such.
In an S-parameter test set - and anyone actually knowing what they talk about please correct me - directional couplers and RF switches do the job of separating the energy flow out of a port from the flow into the port.
Circulators are a particularly clever kind of a directional coupler that¡¯s connected back to itself (at least I think of them that way) - the energy can make it all the way back to the 1st port if the ports on the way reflect it ¡°back¡± - back into the respective ports, but forward in the circulator (there¡¯s an arrow on it that shows which way is ¡°forward¡±, at least on the few I got). A circulator is the RF equivalent of a lazy Susan :)
The ¡°problem¡± with bare VNAs is that the S-parameter test set is a separate device, and a costly one from what I gather, yet one without which the capability of the VNA is quite untapped. The ¡°bare¡± VNA is the RF power source and one or more fancy vector voltmeters. A test set is what connects those up in a circuit that allows a particular kind of very useful measurements (one- and two-port S-parameter measurements). It¡¯s what lets you use those load cells and accelerometers for something useful :)
Best not let the ME ramble too much, though.
Cheers, Kuba
toggle quoted message
Show quoted text
7 mars 2020 kl. 7:41 em skrev Dave McGuire <mcguire@...>:
?On 3/7/20 6:43 PM, David C wrote:
dummy load is a termination with only an input!
If its a parallel connection, yes. Why not a series connection?
VNAs are intended to do "thru' measurments on systems of a
characteristic impedaance (probably 50 ohms) Uhhh...wha?? No. That's one thing that they can do, but the
assertion that they are "intended" to only do thru measurements is
false. Very, very false.
Some are able to do "single port' i.e. connect the load across the TX
port and read that. I've never seen a VNA that is unable to do "single port". And from
where I'm sitting right now I can throw a wad of gum at five different VNAs.
Thats not actually
a 'network analysis' because a dummy load is not exactly a network (read
about Fosters networks). In fact is *is* exactly a network, and performing an S11 analysis on
one is in fact, by definition, network analysis.
Wow. Please read up on what a network is and what VNAs do.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
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Re: HP 8591 external reference connector (1250-1499)
Matthew:
Re: Connector for Ref Osc Intetconnect
It is not special other than being a low profile shape. A BNC - BNC cable will work fine.
If you want a work around - two BNC Male-Female elbows + one BNC Male-Male Barrel space out the same length.
The elbows come in two lengths. Use the shorter.
Hope that helps.
I also have one of these links available - contact me off list....
Dan in Chandler, AZ.
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Re: Testing dummy loads with a VNA
What you missed Jeff is that he didn't state what sort of test equipment he had, and what frequency range he intended to use as well as connector types.
With a modern piece of equipment like the NanoVNA (less than $50 USD) you don't need any accessories; they are all there. The only limitation is the frequency range.
A fancy network analyzer may need many accessories to make a simple S11 measurement (even if only scalar). Without more information from the user, it's a question than can't be answered.
Stuart K6YAZ
Los Angeles, USA
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Re: HP 8591 external reference connector (1250-1499)
On 3/7/20 9:37 PM, medasaro wrote: I am working on getting an HP 89441A up and running (I am trying to
measure the multi-path interference of received ATSC TV signals). Before
I can dive into it, I need to gather the appropriate cables to
interconnect the RF and IF sections. Most are straight forward (BNCs, a
db-9 serial cable, etc) but the adapter needed to connect the reference
output to reference input on the RF section is a bit, well, weird.
According to Keysight Find-A-Part it is HP part number 1250-1499.
Googling that part number brings up little in the way of sources, but
indicates that it was also used on the 8590 series of spectrum
analyzers. Taking a look at the back of my 8591, I could see that it
indeed has one which is pictured below. Now the question is where can I
get another one? Or, if I can't, will an ordinary BNC jumper work? Why
does it need to be this special 1-piece adapter? There's nothing particularly special about it, just use a short piece of decent coaxial cable. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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Re: HP 8591 external reference connector (1250-1499)
A regular BNC cable will work fine.? It's just the "packaging" for?
mechanical convenience.
Daun
Daun E. Yeagley II, N8ASB
On 3/7/2020 9:37 PM, medasaro wrote:
toggle quoted message
Show quoted text
Hi all,
I am working on getting an HP 89441A up and running (I am trying
to measure the multi-path interference of received ATSC TV
signals). Before I can dive into it, I need to gather the
appropriate cables to interconnect the RF and IF sections. Most
are straight forward (BNCs, a db-9 serial cable, etc) but the
adapter needed to connect the reference output to reference input
on the RF section is a bit, well, weird. According to Keysight
Find-A-Part it is HP part number 1250-1499. Googling that part
number brings up little in the way of sources, but indicates that
it was also used on the 8590 series of spectrum analyzers. Taking
a look at the back of my 8591, I could see that it indeed has one
which is pictured below. Now the question is where can I get
another one? Or, if I can't, will an ordinary BNC jumper work? Why
does it need to be this special 1-piece adapter?
Thanks in advance,
Matthew D'Asaro
P.S. I bought the 89441A from a "reputable" surplus equipment
dealer and paid $285 for freight service from LA to Seattle for it
so it would arrive in good condition. It arrived strapped to a
pallet but badly damaged because their ^*&#*&@ shipping
department didn't bother to put a single bit of packing material
around it. The RF and IF sections were literally placed upside
down on top of each other in a bare cardboard box! The box arrived
more or less intact, but the unit was not so lucky... I am working
with the seller for a partial refund (I don't want to try to ship
it back and neither does the seller) but really, people...
|
HP 8591 external reference connector (1250-1499)
Hi all, I am working on getting an HP 89441A up and running (I am trying to measure the multi-path interference of received ATSC TV signals). Before I can dive into it, I need to gather the appropriate cables to interconnect the RF and IF sections. Most are straight forward (BNCs, a db-9 serial cable, etc) but the adapter needed to connect the reference output to reference input on the RF section is a bit, well, weird. According to Keysight Find-A-Part it is HP part number 1250-1499. Googling that part number brings up little in the way of sources, but indicates that it was also used on the 8590 series of spectrum analyzers. Taking a look at the back of my 8591, I could see that it indeed has one which is pictured below. Now the question is where can I get another one? Or, if I can't, will an ordinary BNC jumper work? Why does it need to be this special 1-piece adapter?  Thanks in advance, Matthew D'Asaro P.S. I bought the 89441A from a "reputable" surplus equipment dealer and paid $285 for freight service from LA to Seattle for it so it would arrive in good condition. It arrived strapped to a pallet but badly damaged because their ^*&#*&@ shipping department didn't bother to put a single bit of packing material around it. The RF and IF sections were literally placed upside down on top of each other in a bare cardboard box! The box arrived more or less intact, but the unit was not so lucky... I am working with the seller for a partial refund (I don't want to try to ship it back and neither does the seller) but really, people...
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Re: Advice on Accessories for HP Equipment
At 2020-03-07 10:26 AM, Robert G8RPI via Groups.Io
wrote:
The 8590xE should have?
reference input. It is next to the fan on the rear panel and is conected
to the reference output by a solid bar type BNC to BNC
link.
Aha, thank you for pointing that out. I have pictures of the front and
rear panels of all my equipment for when I want to see if a particular
port is available, without having to disconnect cables and pull them out
of the rack. I have a picture of that one, but the bus bar that connects
the 10 MHz ref out to ref in blocked the view of the text at the angle I
took the picture. Now I see it! I knew it OUGHT to be there.
Steve Hendrix
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Re: 693B sweep oscillator restoration
Just for a slightly alternate view: I think David's advice is sound, but too conservative in some cases. Some comments inserted below. -Pete
toggle quoted message
Show quoted text
On Sat, Mar 7, 2020 at 04:58 PM, David C wrote:
a.) Replace ALL capacitors- electrolytic, tubular paper etc. Theyre probably 50-70 years old. Old caps are monsters waiting to do circuit damage. Ive seen many blow up.
I know that this is very common advice, but if you happen to live in a relatively dry climate, it is much less of an issue. I don't replace caps until I've identified a problem, and for small caps it is rare here in Colorado to see a bad one. Specifically: Electrolytics dry out and lose value easily here. On ordinary commercial radios and such, it is very common to need to replace some. On high-quality test equipment, I usually don't need to do anything to the caps, unless it is VERY old (like an HP200B oscillator that I have). The small caps rarely have issues here, and I believe it is because the failure mode involves absorbing moisture, causing leakage. In this climate, there isn't much moisture... I've never seen a cap "blow up" on quality gear.
b.) Check ALL bias resistors around each tube. A grid resistor going up in value can destroy a plate resistor or do damage other components or a tube.
Good advice to check, but again I don't check unless there is a symptom, which I think is rare.
f.) CRITICAL. Tube gear was made in the "107-115 VAC" AC line voltage era. Vacuum tubes use filaments (heaters) that are very sensitive to filament current (its a current vs. temperature square -function thing).
I just rebuilt a 1990s oscilloscope in which the 4 power supply regulator transistors were screaming hot (burned my finger touching the heat sink)- all because the AC line voltages here now
go to 126 VAC, on a scope intended for 115VAC max.
True that line V these days can be high (I am 124V here). But it's worth checking the rating of the equipment before you panic. And also measure your local line voltage (you may not have an issue). I just looked at a couple of 1950's-vintage HP manuals, and they said "115V". But by the 1960's lots of gear is rated for up to 125V. HP5245L counter (early solid state) is "115 +/-10%". My Tek 561A scope (hybrid tubes and transistors) is marked "105-125". To mellow out a high line voltage: Instead of the resistor approach that David mentions, I would suggest configuring a "buck" transformer, and you can even reduce the voltage for multiple pieces of gear at the same time (mount the bucker inside a large AC outlet box). The resistor method makes a lot of heat, and does not adapt to a changing load. If the equipment's behavior is to present a variable load (such as a DC bench power supply, or an audio amp), then the resistor introduces a *varying* line voltage, which is not good. It's only suitable (at best) for a very specific item that is a fixed load. Another option: a friend of mine has 2 or 3 Variacs, and plugs all of his "important" stuff into them at all times. An expensive but really nice way to deal with it. Pete
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Re: Testing dummy loads with a VNA
First, you did not state what equipment you are using; that makes a lot of difference. Some network analyzers like the NanoVNA are complet and self contained; others are not.
With those ports mentioned, you need a splitter on the output of the network analyzer. One output of the splitter will go to the R input. The other output will go to either a return loss bridge or directional coupler
.
The RF output of a RL bridge will go to the input one or two, if they have an RF input. If not, you will need a compatible detector. If you are using a directional coupler, the coupled arm will go to the detector.
Next, you will have to calibrate the bridge or directional coupler.?
There are many variations depending on the equipment that you have available. Once you have assembled the equipment and accessories, it is relatively simple to calibrate the setup and measure loads.
If you contact me directly I would be happy to provide more information.
Stuart K6YAZ
Los Angeles, USA
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Re: Testing dummy loads with a VNA
On 3/7/20 6:43 PM, David C wrote: dummy load is a termination with only an input!
If its a parallel connection, yes. Why not a series connection?
VNAs are intended to do "thru' measurments on systems of a
characteristic impedaance (probably 50 ohms) Uhhh...wha?? No. That's one thing that they can do, but the assertion that they are "intended" to only do thru measurements is false. Very, very false. Some are able to do "single port' i.e. connect the load across the TX
port and read that. I've never seen a VNA that is unable to do "single port". And from where I'm sitting right now I can throw a wad of gum at five different VNAs. Thats not actually
a 'network analysis' because a dummy load is not exactly a network (read
about Fosters networks). In fact is *is* exactly a network, and performing an S11 analysis on one is in fact, by definition, network analysis. Wow. Please read up on what a network is and what VNAs do. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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Re: 693B sweep oscillator restoration
1. I had a manual problem with my 651B, Found several manuals which had portions with teh same circuit boards as my unit and that was good enough to get by.
2. Barring blowing any of it in sensitive circuits such as open air variable caps, and having a DRY air stream (do NOT use wet compressed air) blow it out. Maybe with an intert gas duster can such as sold for computer keyboards.
Its possible to force moisture in circuits where it wont come out without heat.
3. Welcome to Oz. Tube gear is a specialty of mine. Its a particular problem. Several steps in general:
In general, for all tube gear:
a.) Replace ALL capacitors- electrolytic, tubular paper etc. Theyre probably 50-70 years old. Old caps are monsters waiting to do circuit damage. Ive seen many blow up.
b.) Check ALL bias resistors around each tube. A grid resistor going up in value can destroy a plate resistor or do damage other components or a tube.
c.) Its vital to clean tube pins. No one does it. I remanufacture old Drake ham gear and one of the first items is to spend two tedious hours with 600 grit sandpaper sanding the hard black oxides from the tube pins.
The pins were shiny when new (have replaced lots of them). The cleaned pins will scrape oxides from the inside of the socket pins, so don't do anything to a socket (unless its broken) except maybe spray some
cleaner thru them. Oxidised and bent tube pins can cause erratic operation a/o noise blamed on other circuit problems.
d.) high voltages, of course, are a problem. One can get dead working on tube gear. Learn/Practice the 'one hand in the pocket' rule around tube voltages.
e.) H fields. Build an E field generator to cancel them out.
f.) CRITICAL. Tube gear was made in the "107-115 VAC" AC line voltage era. Vacuum tubes use filaments (heaters) that are very sensitive to filament current (its a current vs. temperature square -function thing).
I just rebuilt a 1990s oscilloscope in which the 4 power supply regulator transistors were screaming hot (burned my finger touching the heat sink)- all because the AC line voltages here now
go to 126 VAC, on a scope intended for 115VAC max. I put a 15 ohm, 5W resistor in series with the power transformer and cooled the heat sinks down to 86 degrees F. Excess line voltage
can destroy tubes, if too high, shorten heater/cathode life, or too low, cause cathode poisoning. Many tubes require 5% filament voltage regulation and if operated from the AC line, may have no regulation built in.
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Re: Testing dummy loads with a VNA
Jinxie,
Ideally, you would use a 85044a transmission / reflection test set. Those things cost quite bit, so you could use some kind of a bridge or coupler instead. A bridge out of a 8505 VNA would work fine to 1.3 GHz and probably even to 2GHz if your 8754 has a doubler.
Vladan
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Re: Testing dummy loads with a VNA
I came in to the middle of this. But I sense mumbo-jumbo.
After 40 years as a professional microwave engineer working with (and owning many) VNA's,I can say definitively that 1 port networks exist, as well as two port, even N port.
Dummy loads, one port devices, are high power terminations, easily assessed with S11 measurements, just like antennas are!
VNA's are not "only" for "thru" measure, not by any means. Thats the secret of the the directivity coupler or bridge!
Why a series connection? Shunt 1 ports are just as easy to evaluate.
A scope and generator will not provide vector measure, as such. Merely scalar.
I guess there must be something more to this thread that I missed. In that case, sorry.
If not, then the author below needs to learn a bit more about VNA's.
Jeff Kruth
In a message dated 3/7/2020 6:43:28 PM Eastern Standard Time, k_8_b_y_p@... writes:
VNAs are intended to do "thru' measurments on systems of a characteristic impedaance (probably 50 ohms) Some are able to do "single port' i.e. connect the load across the TX port and read that. Thats not actually a 'network analysis' because a dummy load is not exactly a network (read about Fosters networks). Why cant you connect the dummy load in series between the TX and another input? (other than the obvious mechanical constraints.)
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Re: Testing dummy loads with a VNA
As Dave said, you need a coupler...probably something like this (although you probably don't need all this frequency range: .?
The basic setup is:
- Connect RF out to the RF input of the coupler (if you need to use R for phase locking, then you will need a splitter to send half to the R input and the other half to the coupler.)
- Connect A, (or B, or C) to the coupled arm
- Place a short or open on coupler test port
- Normalize (grease pencil?)
- Connect your Load.? The drop in the displayed signal is your match.
Caveats:? This is a quick and dirty way to get an approximate measurement, but it is not the most accurate and is heavily dependent upon the source match.? For more accuracy you would need to average out the open and load result and reference to that average.?? Inserting a? good-quality 3 or 6dB? pad before the coupler would help with any source match issues.? I don't remember what the 8754 is capable of.? Modern analyzers handle all the math for you and a one-port cal would consist of measuring an open, a short, and a load.? Once done, you would see basically a flat line at 0.? The load would then be connected and the resulting trace would be your match.
?
?
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medasaro
Dave McGuire
saipan59 (Pete)