Test Equipment Anonymous (TEA) group therapy thread

[med6753]

It's nice but why the open trim pots? Can easily collect dust/dirt and get noisy. Seems cheap to me but otherwise me like. 

[bd139]

Yeah they’re not great to be honest. I’ve had to replace a few over the years. I always go for Bourns cermet ones (genuine ones, not the Chinese rip offs!)

[Specmaster]

@bean, yes the Solartron is that bright but only because when I got it you could see there was a light there at all except in a dark room, I replaced the LEDs with ultra bright ones. I got 2 of those Solartrons and have done both displays and also the dreaded Scheafner filters (bloody expensive) so they should be good for a few years now.

[Specmaster]

It's nice but why the open trim pots? Can easily collect dust/dirt and get noisy. Seems cheap to me but otherwise me like. 

The whole thing TBH is pretty well sealed so dirt is not going to be getting in it really hence it looks like new inside as well.

Yes it is nice but it's manual as well, which it was an Auto but otherwise its really great.

[xrunner]

Nice meter meters Specmaster. 

[mnementh]

Spot the loose nut by the red input jack ?

I'm a lot more worried about the loose voltnut at the front of the thing, myself... 

mnem

[factory]

This nixie DMM looks nice, I have no idea on price though. Expensive, cheap, on the money?

They are worth around $50 or less, also note that the AC & Ohms function buttons are locked out if the option PCB isn't fitted.
Edit: Anyone know why there are two holes in the front panel above the AC & Ohms buttons? 


The last one in the above ePay list was the one @Cubdriver bought, after I posted a link on here. 
Dana 5330 digital voltmeter

David

[Specmaster]

Spot the loose nut by the red input jack ?

I'm a lot more worried about the loose voltnut at the front of the thing, myself... 

mnem

Nah, that is not a cause for any concern because you're in the frozen north otherwise known as Canada....... or are you 

[VK5RC]

Spot the loose nut by the red input jack ?

I'm a lot more worried about the loose voltnut at the front of the thing, myself... 

mnem

Nah - we all have a loose screw around here!

[tggzzz]

Spot the loose nut by the red input jack ?

I'm a lot more worried about the loose voltnut at the front of the thing, myself... 

mnem

Nah - we all have a loose screw around here!

And sometimes it isn't only the 1ns risetime that isn't square...



No, I don't know how they made that cup

[mnementh]

Spot the loose nut by the red input jack ?

I'm a lot more worried about the loose voltnut at the front of the thing, myself... 

mnem

Nah, that is not a cause for any concern because you're in the frozen north otherwise known as Canada....... or are you 

That's okay Spec; there's plenty to go around. We ALL worry about you. 

mnem
For a long time now.

[bd139]

Major bollocks up here. My HF antenna has been rubbing on a wall for the last 4 months apparently. Alas it’s ground a hole through the coax and the braid now and the thing is full of water  .  Sooo 15m of RG58 in the trash and longest bit I have left is 8m. Gonna buy a 100M drum this time.

Edit: nanovna sweep of wet coax would be interesting!

[0culus]

That's frustrating. I would like to see the VNA sweep though... 

[bd139]

Will leave it connected and outside for now. Think nanovna will arrive before a roll of RG58 does!

[mansaxel]

Major bollocks up here. My HF antenna has been rubbing on a wall for the last 4 months apparently. Alas it’s ground a hole through the coax and the braid now and the thing is full of water  .  Sooo 15m of RG58 in the trash and longest bit I have left is 8m. Gonna buy a 100M drum this time.

Edit: nanovna sweep of wet coax would be interesting!

Found I need more short BNC and other connector cables for the bench, so made a few.

And why does this show up as comment to "broken coax"? Well, I've been very happy with SSB-Technik 5mm Aircell coax instead of RG58A/U. I assume the difference to "plain" RG58 (with solid center conductor) is less.  I've got a bunch of Chinese N connectors for RG58 style cable, whose center pin needed drilling out to take the solid core of Aircell 5.    They were cheap, though. And I soldered the pin, for lack of a suitable crimper. A flux pen is your friend.

The other end of that particular cable has a NOS Amphenol milspec solder/clamp BNC. Wonderful connector, probably insanely expensive when new. They consist of no less than 10 parts (Shell, center pin, front insulator, rear insulator, o-ring, braid spreader, washer, gasket, washer, clamp screw) which is a lot compared to the usual pin, shell, crimp ferrule style plug, but go together really easy.

[xrunner]

Edit: nanovna sweep of wet coax would be interesting!

Yes indeed. I've tried the TDR on a ~36 foot piece of RG-8X with the end open and it worked really well and was a very accurate measurement. I'd like to try a 3 or 4 foot piece and damage it like that to see what I see.

[tggzzz]

Major bollocks up here. My HF antenna has been rubbing on a wall for the last 4 months apparently. Alas it’s ground a hole through the coax and the braid now and the thing is full of water  .  Sooo 15m of RG58 in the trash and longest bit I have left is 8m. Gonna buy a 100M drum this time.

Edit: nanovna sweep of wet coax would be interesting!

Told you you need a nice portable battery-powered self-contained Tek 1502 TDR

[bd139]

Major bollocks up here. My HF antenna has been rubbing on a wall for the last 4 months apparently. Alas it’s ground a hole through the coax and the braid now and the thing is full of water  .  Sooo 15m of RG58 in the trash and longest bit I have left is 8m. Gonna buy a 100M drum this time.

Edit: nanovna sweep of wet coax would be interesting!

Found I need more short BNC and other connector cables for the bench, so made a few.

And why does this show up as comment to "broken coax"? Well, I've been very happy with SSB-Technik 5mm Aircell coax instead of RG58A/U. I assume the difference to "plain" RG58 (with solid center conductor) is less.  I've got a bunch of Chinese N connectors for RG58 style cable, whose center pin needed drilling out to take the solid core of Aircell 5.    They were cheap, though. And I soldered the pin, for lack of a suitable crimper. A flux pen is your friend.

The other end of that particular cable has a NOS Amphenol milspec solder/clamp BNC. Wonderful connector, probably insanely expensive when new. They consist of no less than 10 parts (Shell, center pin, front insulator, rear insulator, o-ring, braid spreader, washer, gasket, washer, clamp screw) which is a lot compared to the usual pin, shell, crimp ferrule style plug, but go together really easy.

I don't use the foam stuff as I found it doesn't last as long as the plastic/air cored stuff. When you bend it, the foam slowly gets cut . I haven't measured the loss comparatively to the foam stuff I was buying but on 15m of RG58 I'm losing about 0.6dB over at 7MHz which is nothing to worry about.

I use the solder/clamp BNCs. These aren't the milspec ones but they're just as good and you get a cutting guide for the coax unlike the cheap ones. They are VERY reliable and well made connectors but not at all cheap (£3.58 a go on RS). I've had one outside exposed to the elements for about a year and it's still fine (or was until the coax filled up with water  ).

Edit: nanovna sweep of wet coax would be interesting!

Yes indeed. I've tried the TDR on a ~36 foot piece of RG-8X with the end open and it worked really well and was a very accurate measurement. I'd like to try a 3 or 4 foot piece and damage it like that to see what I see.

I'll do a full report once I've worked out how to use it 

Major bollocks up here. My HF antenna has been rubbing on a wall for the last 4 months apparently. Alas it’s ground a hole through the coax and the braid now and the thing is full of water  .  Sooo 15m of RG58 in the trash and longest bit I have left is 8m. Gonna buy a 100M drum this time.

Edit: nanovna sweep of wet coax would be interesting!

Told you you need a nice portable battery-powered self-contained Tek 1502 TDR

Hahaha. Don't tempt me.

This is my point of reference: https://nuclearrambo.com/wordpress/accurately-measuring-cable-length-with-nanovna/

[mansaxel]

...Aircell 5 ...

The other end of that particular cable has a NOS Amphenol milspec

I don't use the foam stuff as I found it doesn't last as long as the plastic/air cored stuff. When you bend it, the foam slowly gets cut . I haven't measured the loss comparatively to the foam stuff I was buying but on 15m of RG58 I'm losing about 0.6dB over at 7MHz which is nothing to worry about.

Oh, no. Definitely nothing to bother about. 25 metres on 430 MHz is another story, though. There I use Ecoflex 10 from SSB-Technik to a Diamond X300N. Seriously big ears, that.

I use the solder/clamp BNCs. These aren't the milspec ones but they're just as good and you get a cutting guide for the coax unlike the cheap ones. They are VERY reliable and well made connectors but not at all cheap (£3.58 a go on RS). I've had one outside exposed to the elements for about a year and it's still fine (or was until the coax filled up with water  ).

Here's mine:



Indeed, they were expensive. nearly £15 for a plug. I did not pay such money, more like 10% of that price per connector, in a reasonably large bag, large enough to see me set for life. But no cutting guide!

[tggzzz]

Major bollocks up here. My HF antenna has been rubbing on a wall for the last 4 months apparently. Alas it’s ground a hole through the coax and the braid now and the thing is full of water  .  Sooo 15m of RG58 in the trash and longest bit I have left is 8m. Gonna buy a 100M drum this time.

Edit: nanovna sweep of wet coax would be interesting!

Told you you need a nice portable battery-powered self-contained Tek 1502 TDR

Hahaha. Don't tempt me.

Why not 

This is my point of reference: https://nuclearrambo.com/wordpress/accurately-measuring-cable-length-with-nanovna/

I note that states you need a cable with a connector on one end. That isn't strictly true: you can use a short piece of cable  with crochet clips. You should be able to "look past" the crochet clips to see the cable under test. (Yes, there are limitations!)

The 101 steps in a scan looks a limitation: you can have range or resolution, but not both.

[bd139]

Yes but I suspect you can work around the 101 steps by cascading scans if you fancy waiting. The signal source in it, an Si5351A has sub Hz resolution at 300Mhz so there should be no issue there.

I’ve been reading how the NanoVNA works and it’s quite clever. It uses a TLV320 audio codec as a ADC and down converts everything to audio with SA612’s (Gilbert cell mixers) fed from local Si5351. Still working out how the software works. It’s a rats nest. Looks like FFT based but I’m not sure how they get phase info out of that. I imagine that’s separate. Will work it out tomorrow. One big hack though is the output is harmonic heavy. I’m not sure how this affects the measurements it does on harmonics above 900Mhz ie can you set a reference calibration and zero out any unwanted harmonics or if it reduces dynamic range on harmonics. More reverse engineering coming.

[tggzzz]

Not sure how the harmonics affects things, but boat anchor spectrum analysers are harmonic based.

Not sure what you mean about the FFT and phase.

It is a VNA so the phase is available, probably in the form of a complex (IQ) signal. The IFFT operation to convert to the frequency takes the complex input and produces the full time domain output. If the input was a scalar network analyser with no phase information, the time domain output would indicate deviations from 50ohms, but not whether the deviation was positive of negative.

Apart from that, the frequency domain equivalent to a time domain impulse is white noise. Hence if you take the inverse Fourier transform of white noise you get a time domain impulse. Deviations from white noise are equivalent to multiple components in the time domain.

For simplicity, consider an open or short circuit stub which gives time domain echoes. The frequency domain equivalent is a comb filter, where the frequency of the first null depends on the length and whether it is an open or short circuit.

[bd139]

Aware of that. I actually thought IQ to start with but the inputs are both in phase according to the block diagram. Literally three down conversions. Unless there is a software phase shift network in the DSP which seems pointless as they could have just used the third output of the 5351 in the second mixer to get IQ signals into the codec.

https://github.com/ttrftech/NanoVNA/blob/master/doc/nanovna-blockdiagram.png

This is what confused me. I’ve only spent 20  minutes working on this so far though so I may have missed some blindingly obvious things. Im mostly looking at stealing cost savings for a project I’m working on (digimodes only transceiver) 

[mnementh]

Major Bollocks up here. My HF antenna has been rubbing on a wall for the last 4 months apparently. Alas it’s ground a hole through the coax and the braid now and the thing is full of water  .  Sooo 15m of RG58 in the trash and longest bit I have left is 8m. Gonna buy a 100M drum this time.

Edit: nanovna sweep of wet coax would be interesting!

Good evening, Major.    I like the sound of wet gear and RF; the higher the voltage the better.    How long before you let the smoke out of THIS ONE...? 

mnem
*equal-opportunity a-hole* 

[Neomys Sapiens]

@bean, yes the Solartron is that bright but only because when I got it you could see there was a light there at all except in a dark room, I replaced the LEDs with ultra bright ones. I got 2 of those Solartrons and have done both displays and also the dreaded Scheafner filters (bloody expensive) so they should be good for a few years now.

Those pictures convinced me - my 7151 is scheduled for the same procedure.