NanoVNA V2+4 SMA Cal load

[mawyatt]

Just received the mentioned V2+4 VNA and decided to check the supplied SMA 50 ohm load that comes with the cal kit. I measured 50.931 ohms with a new KS34465A, which is considerably higher than the type N load supplied with the SSA-2N version which is 49.634 ohms. Measurements were conducted with the supplied Short establishing the Zero ohm reference for the SMA, and using the type N short for the N Zero ohm reference.

What are others finding with the cal load supplied with the various NanoVNA?

Best,

[joeqsmith]

https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg3323942/#msg3323942

[mawyatt]

Any ohmic (DMM) measurements of Precision Loads?

Best,

[tautech]

Hey Mike, emails direct to you are bouncing back...dunno why. 
Couple of questions but nothing important.
TIA

[cdev]

Related question-
I recently bought a RF resistor advertised as an RF termination.
Not precision.
I don't expect perfection.

Its marked

Logo which is a small v inside a larger ohm symbol
"250NB"
50 (ohms symbol)

Does anybody have any experience with these parts or know where I can find more info or a datasheet?

[mawyatt]

Hey Mike, emails direct to you are bouncing back...dunno why. 
Couple of questions but nothing important.
TIA

Sorry, earthlink email server is down all over US.

Best,

[joeqsmith]

Any ohmic (DMM) measurements of Precision Loads?

Best,

To measure 5 places as you claim to have,  I would need to some sort of 4-wire arrangement.  I would be concerned about touching the pins with anything other than a mating connector.  Then again,  I have little concern about their DC performance. 

Given the choice of a standard that measures 50.0000 ohms and was crap at a 200MHz or a 50.05 ohm that was good out to 6GHz, guess which one I would want to use.   

With the V2+4, working into the 4GHz, I am more concerned with the return loss which is what was shown.   

[joeqsmith]

The following pictures of the standards I had made to demo the original Nano. 

Cal1: HP34401A with 2 wire, banana to BNC, BNC to SMA  to my load.
Cal2/3:  Making a 4-wire measurement at the backside of the loads SMA.   

The DC resistance may far exceed the numbers you show but I can tell you this load is not going to be nearly as good at the parts supplied with my V2+, no matter how good their DC resistance is or isn't, at least not above a GHz. 

SOLT was a snapshot I took from a YT video where they are teaching a class on the nano.  If the DCR was perfect on his loads, do you think it would be any good to use at a GHz?

[mawyatt]

Any ohmic (DMM) measurements of Precision Loads?

Best,

To measure 5 places as you claim to have,  I would need to some sort of 4-wire arrangement.  I would be concerned about touching the pins with anything other than a mating connector.  Then again,  I have little concern about their DC performance. 

Given the choice of a standard that measures 50.0000 ohms and was crap at a 200MHz or a 50.05 ohm that was good out to 6GHz, guess which one I would want to use.   

With the V2+4, working into the 4GHz, I am more concerned with the return loss which is what was shown.

No risk to the load or need for 4 wire setup. I simply used a banana to BNC adapter, then BCN to N or SMA, and then the load. First replace load with the cal short and set DVM to null and null out residual, then replace short with load and make an accurate DCR load reading. No touching or fiddling with the delicate load pins.

Agree 50.05 ohms would be fine, even 50.1 ohms, but starting with almost 51 ohms, then the VSWR minimum for a true 50 ohm measurement will start with a VSWR of 1.02, not 1.000, whereas even if 50.1 ohms were the case then the minimum VSWR would be 1.002.

Just seems that starting out near 50 ohms is a better approach and really doesn't cost anything extra, unless this is to cover an instruments performance at higher frequencies.

Best,

[mawyatt]

The following pictures of the standards I had made to demo the original Nano. 

Cal1: HP34401A with 2 wire, banana to BNC, BNC to SMA  to my load.
BTW no need for the 4 wire, see my post directly above, should be good enough for SMA and N type cal loads.
Cal2/3:  Making a 4-wire measurement at the backside of the loads SMA.
   

The DC resistance may far exceed the numbers you show but I can tell you this load is not going to be nearly as good at the parts supplied with my V2+, no matter how good their DC resistance is or isn't, at least not above a GHz.  What about at 1MHz, or 10MHz or 100MHz??

SOLT was a snapshot I took from a YT video where they are teaching a class on the nano.  If the DCR was perfect on his loads, do you think it would be any good to use at a GHz? Maybe, maybe not, but starting close to 50 is a better than far away, and you'll likely get a better results along your way to 1GHz!!

I previous posted just after this, See my notes above in blue. 

BTW your readings (49.866 and 49.969) are very close to 50 ohms, much closer than what I got with the SAA-2N (49.643) and V2+4 (50.931) cal kits loads. So it seems your loads are in fact starting out very close to 50 ohms, which makes sense, however my V2+4 is almost 51 ohms from the start which raises some questions

Best,

[joeqsmith]

If I could just null and get 3 places beyond the decimal. 

The problem I see with the short is the center pin rotates.  Say you bought a new SMA adapter and start twisting that center pin around in your new part.  Worse, you didn't inspect the short to make sure it had no burrs.   Now you plug your new load into a connector you just damaged.   The damage spreads like covid and soon you are left with a mess.   

You really want to know how well the standards behave at the frequencies you plan to use them.  You won't get that answer with even an 8 place DMM.

Even if the parts from my V2+/4 were 51 ohms DC, they would still far out perform that standard I show, except at very low frequencies.  The meter is still on, so for fun here is some more DC resistances without nulling the meter:

Custom PCB standard short: 0.015   This is the short shown in the previous picture.
NanoVNA V2+ standard:  51.021
Mini-circuits ANNE: 49.822  Used to replace the original part and shown in that graph I linked.
Cheap unknown BNC Ethernet terminator: 49.921

I would guess that BNC terminator is the worse of the four for RF work.  I wouldn't be surprised to find an axial part inside if I cut it open.  But again, if your goal is only to make measurements at very low frequencies, sure.   Are you trying to measure SWR at 4MHz or 4GHz?  You can get away with a lot below 100MHz.   I made this RF circuit, which I am very proud of, to demonstrate this point:
https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg2924286/#msg2924286

Skip down to my next post and you can see it running at 300MHz with one small change.. 

*****
That picture I showed of the two gentlemen teaching a class on how to use the nano makes sense if the standards they show are for the HF bands.  Still, very poor construction like the attenuator I show in that link.   Not something I would show other than to make a point.   

Hope this all helps. 

[mawyatt]

If I could just null and get 3 places beyond the decimal. 

The problem I see with the short is the center pin rotates.  Say you bought a new SMA adapter and start twisting that center pin around in your new part.  Worse, you didn't inspect the short to make sure it had no burrs.   Now you plug your new load into a connector you just damaged.   The damage spreads like covid and soon you are left with a mess.   

So how do you do a quality cal without using a proper short since you seem reluctant to use it??

Try not to twist the pins, either on the SMAs or the type N, and also tend to check things out. Coming from an IC design world (retired now) used to things considerably more delicate than these connectors and much much smaller too

You really want to know how well the standards behave at the frequencies you plan to use them.  You won't get that answer with even an 8 place DMM.

Even if the parts from my V2+/4 were 51 ohms DC, they would still far out perform that standard I show, except at very low frequencies.  The meter is still on, so for fun here is some more DC resistances without nulling the meter:

Custom PCB standard short: 0.015   This is the short shown in the previous picture.
NanoVNA V2+ standard:  51.021
Interesting, seems your V2+ is also ~51 ohms which confirms what I was told that this is used to help the V2+ meet a RL of 35dB at 3GHz by using a 51 ohm rather than a traditional 50 ohm standard load for calibration.
Mini-circuits ANNE: 49.822  Used to replace the original part and shown in that graph I linked.
Cheap unknown BNC Ethernet terminator: 49.921

I would guess that BNC terminator is the worse of the four for RF work.  I wouldn't be surprised to find an axial part inside if I cut it open.  But again, if your goal is only to make measurements at very low frequencies, sure.   Are you trying to measure SWR at 4MHz or 4GHz?  Depends on what I'm doing, would like something that is good enough over the DC to 3GHz range now without too much uncertainty, later much higher if we get involved with 5G chip designs but then cost won't matter and it won't be out-of-pocket, so likely a KS VNA with KS cal kit. You can get away with a lot below 100MHz.   I made this RF circuit, which I am very proud of, to demonstrate this point:
https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg2924286/#msg2924286

Skip down to my next post and you can see it running at 300MHz with one small change.. 

*****
That picture I showed of the two gentlemen teaching a class on how to use the nano makes sense if the standards they show are for the HF bands.  Still, very poor construction like the attenuator I show in that link.   Not something I would show other than to make a point. 

I'm surprised it worked as well as it did using those 1/8w resistors with so much lead inductance, also not surprised you found some notches for the same reason, nice demo too.

Hope this all helps.

My notes above in blue.

With your V2+ measurement of 51.021 ohms this confirms what I was told why these are centered at ~51 ohms and not 50 ohms. So apparently the V2+ needs a 51 ohm cal to help with the RL at higher frequencies.

So for reference if you use a cal load other than ~51 ohms (50 for example) with the V2+ then expect a slightly poorer RL at higher frequencies, and if you use a cal load of ~51 ohms expect a VSWR minimum of 1.02, not 1.000 for an ideal 50 ohm termination.

Thanks for the measurements, now I know why these V2+ cal loads are ~51 ohms

Best,

[joeqsmith]

So how do you do a quality cal without using a proper short since you seem reluctant to use it??

The short of it, I don't.  And get this, I don't care.  For my home use, getting in the ballpark is good enough. 

Try not to twist the pins, either on the SMAs or the type N, and also tend to check things out. Coming from an IC design world (retired now) used to things considerably more delicate than these connectors and much much smaller too

For the SMA, the center pin is locked to the cap.  They turn together.   There is going to be a lot of twisting going on.   

Interesting, seems your V2+ is also ~51 ohms which confirms what I was told that this is used to help the V2+ meet a RL of 35dB at 3GHz by using a 51 ohm rather than a traditional 50 ohm standard load for calibration.

If this was something someone had posted on a forum, post a link.  I would like to read the whole discussion.

Depends on what I'm doing, would like something that is good enough over the DC to 3GHz range now without too much uncertainty, later much higher if we get involved with 5G chip designs but then cost won't matter and it won't be out-of-pocket, so likely a KS VNA with KS cal kit.

Retired but still doing chip designs?  I must have missed something.  No matter.   

My early home experiments in the >2GHz may have been educational but that's about it.  I would be pretending to suggest otherwise. 

...

With your V2+ measurement of 51.021 ohms this confirms what I was told why these are centered at ~51 ohms and not 50 ohms. So apparently the V2+ needs a 51 ohm cal to help with the RL at higher frequencies.

So for reference if you use a cal load other than ~51 ohms (50 for example) with the V2+ then expect a slightly poorer RL at higher frequencies, and if you use a cal load of ~51 ohms expect a VSWR minimum of 1.02, not 1.000 for an ideal 50 ohm termination.

Thanks for the measurements, now I know why these V2+ cal loads are ~51 ohms

Best,

I would like to read this thread.  Post a link.   

I don't know about the embedded firmware for the V2+ but I would expect if I cal the unit to 40ohms and install a 40ohm load, the SWR is going to be 1.  You should be able to calibrate the VNA to any standards you come up with and those standards will be the new norm.   That said, if the V2+ were designed for say 75 ohms and we are trying to use it with 50 ohms, sure that's a problem.

[mawyatt]

So how do you do a quality cal without using a proper short since you seem reluctant to use it??

The short of it, I don't.  And get this, I don't care.  For my home use, getting in the ballpark is good enough. 

Try not to twist the pins, either on the SMAs or the type N, and also tend to check things out. Coming from an IC design world (retired now) used to things considerably more delicate than these connectors and much much smaller too

For the SMA, the center pin is locked to the cap.  They turn together.   There is going to be a lot of twisting going on. 

The SMAs I have the cap can be held while rotating the hex nut to tighten, some easier than others. There is always the chance of some rotation, so carefully attention is necessary to keep the rotation to a minimum.

Interesting, seems your V2+ is also ~51 ohms which confirms what I was told that this is used to help the V2+ meet a RL of 35dB at 3GHz by using a 51 ohm rather than a traditional 50 ohm standard load for calibration.

If this was something someone had posted on a forum, post a link.  I would like to read the whole discussion.

This came directly from HCXQS (designers of the V2+) when I inquired about the ~51 ohm load.

Depends on what I'm doing, would like something that is good enough over the DC to 3GHz range now without too much uncertainty, later much higher if we get involved with 5G chip designs but then cost won't matter and it won't be out-of-pocket, so likely a KS VNA with KS cal kit.

Retired but still doing chip designs?  I must have missed something.  No matter.

I've been a consultant, an adjunct prof, and an occasional expert witness (patent cases, have 30+ patents so know this area) for most of my career. So when I retired from my normal daytime job (Chief Engineer/Scientist) still have some potential work going on. As you know there is a lot of interest in highly integrated RF and MW systems with 5G coming on board, and integration is the key to lower cost. The opportunity for a highly integrated 5G SoC (System on Chip) is possible and a few folks I know are working towards this. With TSMC already supplying Apple with 5 nanometer CMOS in their new products (M1 has over 13 billion CMOS devices), production 5nm is quite amazing even for someone in this semiconductor field, the integration of a 5G SoC will happen soon I believe. So I may be able to get involved with some chip design as a consultant after retiring 

My early home experiments in the >2GHz may have been educational but that's about it.  I would be pretending to suggest otherwise. 

...

With your V2+ measurement of 51.021 ohms this confirms what I was told why these are centered at ~51 ohms and not 50 ohms. So apparently the V2+ needs a 51 ohm cal to help with the RL at higher frequencies.

So for reference if you use a cal load other than ~51 ohms (50 for example) with the V2+ then expect a slightly poorer RL at higher frequencies, and if you use a cal load of ~51 ohms expect a VSWR minimum of 1.02, not 1.000 for an ideal 50 ohm termination.

Thanks for the measurements, now I know why these V2+ cal loads are ~51 ohms

Best,

I would like to read this thread.  Post a link.   

As mentioned above, this came directly from HCXQS about using 51 ohms to help with 3GHz RL.

I don't know about the embedded firmware for the V2+ but I would expect if I cal the unit to 40ohms and install a 40ohm load, the SWR is going to be 1.  You should be able to calibrate the VNA to any standards you come up with and those standards will be the new norm.   That said, if the V2+ were designed for say 75 ohms and we are trying to use it with 50 ohms, sure that's a problem.

Notes above in blue.

BTW I agree that just playing around with this stuff at any frequency at home is fun. Most of my later career was advanced research into SOTA system and chip designs, so was spent doing research, writing papers (mostly proprietary), giving presentations (also proprietary), and doing simulations to acquire funding. The lab was generally off limits since my perceived value added was higher doing the above (and mentoring) and not in the lab. I really missed the "hands on" lab stuff so jumped at the opportunity to get some decent test equipment and play around at home when I retired

Best,

[dougg]

Just received the mentioned V2+4 VNA and decided to check the supplied SMA 50 ohm load that comes with the cal kit. I measured 50.931 ohms with a new KS34465A, which is considerably higher than the type N load supplied with the SSA-2N version which is 49.634 ohms. Measurements were conducted with the supplied Short establishing the Zero ohm reference for the SMA, and using the type N short for the N Zero ohm reference.

What are others finding with the cal load supplied with the various NanoVNA?

Best,

I have the same model. Measured with LCR Pro1 Plus tweezers at 100 kHz and 1 Volt rms, I get 51.08 Ohms on the 50 ohm terminator that came with the nanoVNA. Similar numbers at lower frequencies. The LCR specs claim 0.5% accuracy in the 100 Ohm resistance range @ 1 Volt rms, 0.2% accuracy at lower frequencies. The LCR shows a phase on resistance (between voltage and current I assume) and with the 51.08 Ohm measurement it was showing 0.12 degrees.

[mawyatt]

Just received the mentioned V2+4 VNA and decided to check the supplied SMA 50 ohm load that comes with the cal kit. I measured 50.931 ohms with a new KS34465A, which is considerably higher than the type N load supplied with the SSA-2N version which is 49.634 ohms. Measurements were conducted with the supplied Short establishing the Zero ohm reference for the SMA, and using the type N short for the N Zero ohm reference.

What are others finding with the cal load supplied with the various NanoVNA?

Best,

I have the same model. Measured with LCR Pro1 Plus tweezers at 100 kHz and 1 Volt rms, I get 51.08 Ohms on the 50 ohm terminator that came with the nanoVNA. Similar numbers at lower frequencies. The LCR specs claim 0.5% accuracy in the 100 Ohm resistance range @ 1 Volt rms, 0.2% accuracy at lower frequencies. The LCR shows a phase on resistance (between voltage and current I assume) and with the 51.08 Ohm measurement it was showing 0.12 degrees.

These seem to jive with what Joe and I have measured. Also adds credibility to this 51 ohms is intentional and not a sloppy 50 ohms, confirming what was said about helping the V2+ with better higher frequency RL.

Thanks for the measurements,

Best,

[joeqsmith]

The SMAs I have the cap can be held while rotating the hex nut to tighten, some easier than others. There is always the chance of some rotation, so carefully attention is necessary to keep the rotation to a minimum.

Mine doesn't have enough of a nub to hold it securely with my fingers or tweezers.   I could maybe solder a nut to the backside to hold it with a wrench.  At least with the new load, the end is long enough to grab hold of. 

This came directly from HCXQS (designers of the V2+) when I inquired about the ~51 ohm load.
...
As mentioned above, this came directly from HCXQS about using 51 ohms to help with 3GHz RL.

Can you provide a link, or just post their response with your original question?  There is something curious about the need for it in the first place and then the presented justification.  If the Nano was actually designed to with with slight miss match from 50 ohms,  that's really odd. 

You seem to have an interest in SWR, or at least mention it a lot, down to three places.   Is it really this big of a deal for you to try and measure SWR this many places out?  If so, why? 

For me, 51-49 good enough IF the part is well behaved over the range I want to use it.   If I still played with radios, that bit of error in an SWR reading would be of no concern to me.   

[cdev]

Are there any RF-derived calculations you can remember where an small error ends up multiplying, so ends up being important? With the caveat that there is a chance I am thinking about something else, I am around, say 80-85% sure that at some point a few weeks ago, after I got my Nanovna 2 - while reading about VNAs, I read that that minimal (SWR?) error was highly desirable with some VNA based calculations, (come to think of it I suspect that it was in one of those QEX articles I mentioned previously) because the errors multiplied and would totally throw some (infrequently done?) measurements way off.
It might have been in a discussion about the precision available with different hardware means of implementing VNAs or some such? I don't remember!

Arrgh.. I hate getting old..

I made a mental note to myself to remember the specifics but now I cant remember what the reason is. That's almost worse than nothing, I'm sorry.

[joeqsmith]

100 ohms on a 50 ohm system is 2:1 or an SWR of 2.   What's 51/50?  < a tenth?   Would any amateur radio or CBer (or anyone else involved with antennas)  really care?    Based on these posts, it seems like there are a few or at least one, but I don't know why. 

[mawyatt]

The SMAs I have the cap can be held while rotating the hex nut to tighten, some easier than others. There is always the chance of some rotation, so carefully attention is necessary to keep the rotation to a minimum.

Mine doesn't have enough of a nub to hold it securely with my fingers or tweezers.   I could maybe solder a nut to the backside to hold it with a wrench.  At least with the new load, the end is long enough to grab hold of. 

This came directly from HCXQS (designers of the V2+) when I inquired about the ~51 ohm load.
...
As mentioned above, this came directly from HCXQS about using 51 ohms to help with 3GHz RL.

Can you provide a link, or just post their response with your original question?

I don't provide private emails details on a public forum, that's just irresponsible and violates the other parties trust. Sure I could issue a request, but why don't you ask yourself if you question my explanation??

There is something curious about the need for it in the first place and then the presented justification.  If the Nano was actually designed to with with slight miss match from 50 ohms,  that's really odd. 

I doubt this was a fundamental design choice, why would you want to use 51 ohms instead of 50 ohms?? More likely a compensation means to improve the performance of an already pretty good product, maybe they had a higher than expected RL in the upper frequency ranges. That's the reason I asked why the 51 ohms, I initially thought it was an out of spec 50 ohm load, and got the response because it makes the higher frequency RL better. After finding you and Doug also have 51 ohm loads with the V2+, then this makes sense as it is intentional and is good enough answer AFAIC.

You seem to have an interest in SWR, or at least mention it a lot, down to three places.   Is it really this big of a deal for you to try and measure SWR this many places out?  If so, why? 
It's just easier to calculate in your head, simple as that.
For me, 51-49 good enough IF the part is well behaved over the range I want to use it.   If I still played with radios, that bit of error in an SWR reading would be of no concern to me.

Some responses in blue above.

Agree, generally this 49-51 range is fine but I wanted to understand the root reason for the 51 ohms, was this a sloppy load or was it intentional. Now I know the answer. Leaving things "out in the bush" has a habit of allowing Murphy in at some point, and he will bite and bite hard, I know I have "teeth" marks to prove it 

So having a cal load of 51 ohms could have some impact on precision measurements at some time, and it's better to know the reasoning behind the decision rather than sweep in under the rug and open one's self up for a possible issue later. Sure I wouldn't rely on the V2+ for any precision work, but might use it to verify another measurement from a precision instrument as a sanity check. When you come from the IC design world you learn to make sure you understand everything possible about what you are doing and what you are using, because a single simple mistake or mis-calculation, or mis-measurement can cost millions of $. Unlike the PCB world where a respin only cost a few $, and takes only a week or so, an IC fab respin can cost millions (10 years ago a 45nm SOI CMOS mask set cost over $4M, think what a SOTA 5, 7 or 10nm CMOS mask set cost today!!) and take many many months to process, so you do your best to keep Murphy out from the get go

Best

[joeqsmith]

I don't provide private emails details on a public forum, that's just irresponsible and violates the other parties trust. Sure I could issue a request, but why don't you ask yourself if you question my explanation??

Yes, I question your explanation as to why the supplied load resistor would be 51 ohms.  There are no facts associated with it.  I have no details from the source and you are reluctant to supply it.  My guess is they found some 51 ohm parts with a better return loss over the working range of the Nano than 50 ohm parts.    I find it far more believable the return loss is better because of the quality of the part they found rather than its DC resistance. 

I doubt this was a fundamental design choice, why would you want to use 51 ohms instead of 50 ohms?? More likely a compensation means to improve the performance of an already pretty good product, maybe they had a higher than expected RL in the upper frequency ranges. That's the reason I asked why the 51 ohms, I initially thought it was an out of spec 50 ohm load, and got the response because it makes the higher frequency RL better. After finding you and Doug also have 51 ohm loads with the V2+, then this makes sense as it is intentional and is good enough answer AFAIC.

Right, lots of maybes.  Little facts.   This is why I question your comments. 

You seem to have an interest in SWR, or at least mention it a lot, down to three places.   Is it really this big of a deal for you to try and measure SWR this many places out?  If so, why? 
It's just easier to calculate in your head, simple as that.

I find swagging to 1 place beyond the decimal easier than sorting out 3 places.   SWR to 3 places out makes no sense to me.   

Agree, generally this 49-51 range is fine but I wanted to understand the root reason for the 51 ohms, was this a sloppy load or was it intentional. Now I know the answer. Leaving things "out in the bush" has a habit of allowing Murphy in at some point, and he will bite and bite hard, I know I have "teeth" marks to prove it 

So having a cal load of 51 ohms could have some impact on precision measurements at some time, and it's better to know the reasoning behind the decision rather than sweep in under the rug and open one's self up for a possible issue later. Sure I wouldn't rely on the V2+ for any precision work, but might use it to verify another measurement from a precision instrument as a sanity check. ...

True, it's good to understand any tools you use.  But we still do not know why the 51 ohm was chosen.   I doubt is has anything at all to do with the V2+'s hardware but just the quality of the parts they found. 

I was thinking about that short.  So I made up an end cap and soldered to the back side.  Fits a standard 5/16" wrench. 

[mawyatt]

I don't provide private emails details on a public forum, that's just irresponsible and violates the other parties trust. Sure I could issue a request, but why don't you ask yourself if you question my explanation??

Yes, I question your explanation as to why the supplied load resistor would be 51 ohms.  There are no facts associated with it.  I have no details from the source and you are reluctant to supply it.  My guess is they found some 51 ohm parts with a better return loss over the working range of the Nano than 50 ohm parts.    I find it far more believable the return loss is better because of the quality of the part they found rather than its DC resistance. 

Why don't you contact the OEM and quit wasting my and everyone else's time. I've provided the info on the V2+ OEM above, they are source as mentioned, it seems you are reluctant to contact them??

I doubt this was a fundamental design choice, why would you want to use 51 ohms instead of 50 ohms?? More likely a compensation means to improve the performance of an already pretty good product, maybe they had a higher than expected RL in the upper frequency ranges. That's the reason I asked why the 51 ohms, I initially thought it was an out of spec 50 ohm load, and got the response because it makes the higher frequency RL better. After finding you and Doug also have 51 ohm loads with the V2+, then this makes sense as it is intentional and is good enough answer AFAIC.

Right, lots of maybes.  Little facts.   This is why I question your comments.

Again why are you reluctant to contact the OEM yourself, maybe do a little research on your own rather than ask others to do it for you!!

You seem to have an interest in SWR, or at least mention it a lot, down to three places.   Is it really this big of a deal for you to try and measure SWR this many places out?  If so, why? 
It's just easier to calculate in your head, simple as that.

I find swagging to 1 place beyond the decimal easier than sorting out 3 places.   SWR to 3 places out makes no sense to me.

 Well if you are into "swagging" measurements then this wouldn't make sense to you, even claiming to not worry about doing a short cal, so one decimal place is probably fine!!   

Agree, generally this 49-51 range is fine but I wanted to understand the root reason for the 51 ohms, was this a sloppy load or was it intentional. Now I know the answer. Leaving things "out in the bush" has a habit of allowing Murphy in at some point, and he will bite and bite hard, I know I have "teeth" marks to prove it 

So having a cal load of 51 ohms could have some impact on precision measurements at some time, and it's better to know the reasoning behind the decision rather than sweep in under the rug and open one's self up for a possible issue later. Sure I wouldn't rely on the V2+ for any precision work, but might use it to verify another measurement from a precision instrument as a sanity check. ...

True, it's good to understand any tools you use.  But we still do not know why the 51 ohm was chosen.   I doubt is has anything at all to do with the V2+'s hardware but just the quality of the parts they found.

Not we, its seems like you don't know, so actually more speculation on your part, maybe it's time to contact the OEM so you can enlighten yourself!!

I was thinking about that short.  So I made up an end cap and soldered to the back side.  Fits a standard 5/16" wrench.
 
Like this??

Notes above in purple.

Best,

[joeqsmith]

I don't provide private emails details on a public forum, that's just irresponsible and violates the other parties trust. Sure I could issue a request, but why don't you ask yourself if you question my explanation??

Yes, I question your explanation as to why the supplied load resistor would be 51 ohms.  There are no facts associated with it.  I have no details from the source and you are reluctant to supply it.  My guess is they found some 51 ohm parts with a better return loss over the working range of the Nano than 50 ohm parts.    I find it far more believable the return loss is better because of the quality of the part they found rather than its DC resistance. 

Why don't you contact the OEM and quit wasting my and everyone else's time. I've provided the info on the V2+ OEM above, they are source as mentioned, it seems you are reluctant to contact them??

I doubt this was a fundamental design choice, why would you want to use 51 ohms instead of 50 ohms?? More likely a compensation means to improve the performance of an already pretty good product, maybe they had a higher than expected RL in the upper frequency ranges. That's the reason I asked why the 51 ohms, I initially thought it was an out of spec 50 ohm load, and got the response because it makes the higher frequency RL better. After finding you and Doug also have 51 ohm loads with the V2+, then this makes sense as it is intentional and is good enough answer AFAIC.

Right, lots of maybes.  Little facts.   This is why I question your comments.

Again why are you reluctant to contact the OEM yourself, maybe do a little research on your own rather than ask others to do it for you!!

You seem to have an interest in SWR, or at least mention it a lot, down to three places.   Is it really this big of a deal for you to try and measure SWR this many places out?  If so, why? 
It's just easier to calculate in your head, simple as that.

I find swagging to 1 place beyond the decimal easier than sorting out 3 places.   SWR to 3 places out makes no sense to me.

 Well if you are into "swagging" measurements then this wouldn't make sense to you, even claiming to not worry about doing a short cal, so one decimal place is probably fine!!   

Agree, generally this 49-51 range is fine but I wanted to understand the root reason for the 51 ohms, was this a sloppy load or was it intentional. Now I know the answer. Leaving things "out in the bush" has a habit of allowing Murphy in at some point, and he will bite and bite hard, I know I have "teeth" marks to prove it 

So having a cal load of 51 ohms could have some impact on precision measurements at some time, and it's better to know the reasoning behind the decision rather than sweep in under the rug and open one's self up for a possible issue later. Sure I wouldn't rely on the V2+ for any precision work, but might use it to verify another measurement from a precision instrument as a sanity check. ...

True, it's good to understand any tools you use.  But we still do not know why the 51 ohm was chosen.   I doubt is has anything at all to do with the V2+'s hardware but just the quality of the parts they found.

Not we, its seems like you don't know, so actually more speculation on your part, maybe it's time to contact the OEM so you can enlighten yourself!!

I was thinking about that short.  So I made up an end cap and soldered to the back side.  Fits a standard 5/16" wrench.
 
Like this??

Notes above in purple.

Best,

I didn't start the thread asking the question and suggesting to know the reason why.   No need to get upset because you don't have data or that I question your thoughts on the matter.  I acknowledged I didn't know when I wrote " My guess is they found ..."    I made no claims otherwise.   Why would I contact anyone.  I've stated,  I don't have a need to measure to such accuracy.   

If you are not sure what the designer have explained to you in your private conversation, then why ask in the public forums.  Just ask them for further explanation. 

I am not sure what your picture is showing.  Is this what was supplied with your V2+ for a short??  If so, that not even close to what they supplied with mine. 

Attached looking at SWR for three different resistors.   If you think that yellow is the best part, you would be wrong.  Red is actually the best of the three.  Because SI=SO.

[xrunner]

100 ohms on a 50 ohm system is 2:1 or an SWR of 2.   What's 51/50?  < a tenth?   Would any amateur radio or CBer (or anyone else involved with antennas)  really care?    Based on these posts, it seems like there are a few or at least one, but I don't know why.

I'm a ham and I wouldn't care. Nothing I do in ham radio would need to be any more accurate.

[joeqsmith]

Thanks for confirming.   I have still have my old Mars SWR meter and I don't think I could use it to read 1.1 squinting my eyes.       


Capture 2, red trace is the terminator that had the best DC resistance of the four. 
Capture 3, Zooming in the red and yellow converge at 1.001.  The two worse parts of the four.  Red is the Ethernet terminator.  yellow is my home made PCB standards.  V2+ was calibrated using my PCB standard.   

I thought that the Kirkby video was a straight to the point demonstration.  Wonder why so many down votes.