Test Equipment Anonymous (TEA) group therapy thread

[AVGresponding]

I still reckon it was something like that which caused the Greenfell fire. https://en.wikipedia.org/wiki/Grenfell_Tower_fire#Initial_fire_(00:50–01:15)

I thought the fridge fire was pretty much accepted as the source? The owner of the fridge phoned the fire service to report it quite early on iirc.

[tggzzz]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

Mine's packed away so I'll leave it as an exercise for capt bullshot to learn more about VNA mode in his new toy.

Gunna do like menm so off to ded and will check how he's getting on with it tomorrow.

To be honest a Time Domain Reflectometer (TDR) is better for spotting wrong impedance connectors and crimped cables than a basic VNA. VNAs don't natively show distance. The modern ones have a "Distance to Fault" function that provides a TDR like display by applying a FFT.

I agree that a good TDR is better than a VNA, but a VNA will indicate distance via the frequency of the nulls. Yes, the null frequency will depend on propagation velocity, but TDRs have the same issue.

BTW, frequency->time is by the inverse FFT.

[bd139]

I still reckon it was something like that which caused the Greenfell fire. https://en.wikipedia.org/wiki/Grenfell_Tower_fire#Initial_fire_(00:50–01:15)

I thought the fridge fire was pretty much accepted as the source? The owner of the fridge phoned the fire service to report it quite early on iirc.

Yeah it is. Thinking a closer look at what in the fridge caught fire is probably a good idea. Heard nothing about that so far.

Talking of which need to replace my fridge. Compressor is not making happy noises. Had it 12 years approx so not complaining.

[AVGresponding]

I still reckon it was something like that which caused the Greenfell fire. https://en.wikipedia.org/wiki/Grenfell_Tower_fire#Initial_fire_(00:50–01:15)

I thought the fridge fire was pretty much accepted as the source? The owner of the fridge phoned the fire service to report it quite early on iirc.

Yeah it is. Thinking a closer look at what in the fridge caught fire is probably a good idea. Heard nothing about that so far.

Talking of which need to replace my fridge. Compressor is not making happy noises. Had it 12 years approx so not complaining.

Oh, ok. Yes well, hard to think of another likely culprit, assuming no owner modifications such as a blown fuse wrapped in foil and re-used etc.

[tggzzz]

Talking of which need to replace my fridge. Compressor is not making happy noises. Had it 12 years approx so not complaining.

Bought my fridge (and dishwasher) in '88 and my freezer in ~'97

[AVGresponding]

The fridge I modified to use as an air source heat pump must be well over 30 years old.

My SIL's father is an HVAC engineer and we have chatted about a/c and what are common faults, and the subject of compressors did come up.
Seems the lubricating oil for the pump is not separated from the refrigerant (if I understood what he was telling me), and so you are told to let a fridge etc stand for an hour or two after transporting it so that the oil can properly drain back into the pump, in case it's managed to get into the pipework.

I expect running it without the full complement of oil is likely to shorten the service life to some degree.

[Specmaster]

Probably quite a lot of the failures are thermal issues.

As we all know, modern LED lighting is run way harder than it should be, in order to ensure an MTBF that keeps the factories in work.
There is information for the installer in the fitting instructions that tells you not to cover the top side, and how much air space is needed above it, but they are frequently installed by people that can't be arsed to read these things, either because "I've been an electrician for (insert suitable number) years, and I don't need to be told how to fit a light", or the younger ones who just don't give a toss.

I found Big Clive's recent vid on the "Dubai LED lamps" quite interesting. For sure when they start to sell them here, they will a) charge a premium, and b) find another way to bring the MTBF down.

Yes you're right, there are some extremely clever electricians out there. I once had to drop everything and make a quick dash from London to the Metro Centre in Newcastle upon Tyne and back on the same day. A contractor fitting out a T Mobile shop was using the specified lighting control system which was dumb marshalling boxes with some plug-in semi intelligent control modules that used plugin logic blocks and a 6 and 4 core data cables (RJ25 and RJ14 plugs) to connect the control modules in together in various ways to form circuits / groups / functions as required. It was reported that 1 day prior to hand over the contractor had decided to test the lighting and only 1 marshalling box was working.

When I arrived I walked into the back storeroom and discovered all the instructions along with my schematic for the installation in a heap of rubbish that was being chucked into a skip by the loading bay. The contractor confessed that he never looked at any of them as he had done commercial lighting many times before, that was his first mistake.

Opening up the only working marshalling box, My suspicions were confirmed, the mains supply was supposed to be looped from the first box onto the others, but there were no cables between marshalling boxes other than the data cable. The Contractor said that he thought the mains was carried between them via the data cable  All the cables were neatly attached to a suspended ladder tray. I got him to run mains cables between them while I set to plug in the correct logic blocks in the right order to provide the level of control that T-Mobile specified for their shops. Within a short space of time it was all up and running correctly and when the T-Mobile inspector and other top staff turned up for the hand-over, it all went smoothly.

That was not an isolated incident either, had others along similar lines at Oxford Street in London and another in Dartford shopping mall. Where do they find their contractors FFS 

[med6753]

How did I wind up 2.5 pages behind? It is Sunday morning, right? Or is it Monday?  Damn, can't shake the sleepy and yawning. Need more coffee. 

Calendar sez Sunday.....I think. 

[Specmaster]

I still reckon it was something like that which caused the Greenfell fire. https://en.wikipedia.org/wiki/Grenfell_Tower_fire#Initial_fire_(00:50–01:15)

I thought the fridge fire was pretty much accepted as the source? The owner of the fridge phoned the fire service to report it quite early on iirc.

Yeah it is. Thinking a closer look at what in the fridge caught fire is probably a good idea. Heard nothing about that so far.

Talking of which need to replace my fridge. Compressor is not making happy noises. Had it 12 years approx so not complaining.

Yes it was blamed on the fridge, possibly a starting cap blew up, setting fire to the almost obligatory white plastic rear panel behind the radiator that is on fridges these days.

[med6753]

Talking of which need to replace my fridge. Compressor is not making happy noises. Had it 12 years approx so not complaining.

It may just need a refrigerant recharge. Problem is finding someone to do it properly. You don't just "top it off" and call it good as many hacks will attempt. Proper method is pump down and recovery of all old refrigerant and leak check. Then recharge with new refrigerant and compressor oil.

 

[med6753]

I still reckon it was something like that which caused the Greenfell fire. https://en.wikipedia.org/wiki/Grenfell_Tower_fire#Initial_fire_(00:50–01:15)

I thought the fridge fire was pretty much accepted as the source? The owner of the fridge phoned the fire service to report it quite early on iirc.

Yeah it is. Thinking a closer look at what in the fridge caught fire is probably a good idea. Heard nothing about that so far.

Talking of which need to replace my fridge. Compressor is not making happy noises. Had it 12 years approx so not complaining.

Yes it was blamed on the fridge, possibly a starting cap blew up, setting fire to the almost obligatory white plastic rear panel behind the radiator that is on fridges these days.

I remember seeing that fire on TV which just reinforced my fear that I would never, ever, live in a high rise tower. But unfortunately some people have no choice for a variety of reasons.

[Cerebus]

More Rifa Madness!
In my last test run I forgot an old HP battery inverter 85901A, the 20Ahr 12V sealed lead acid battery needed a good charge. About an hour in, that lovely smell, a crack and a bit of smoke arose. One of the weird things was as they died, (they took out the mains fuse - not unexpectedly) but sent little spitballs of molten metal with the lovely tarry rifa residue over an area of about 4 square inches of the pcb. Photos below - cleaned up OK - two new X caps and a new fuse and all is happy 👍
Edit - I have not seen the little metal balls before re rifa 'accidents'

I wonder if it ought to be considered good practice to coat the PCB near a RIFA with welder's anti-spatter spray? 

[Cerebus]

OMG I just watched a Hermes driver trying to get a fishing pole through someone’s letterbox 

 

Actually crying tears of laughter here.

[tggzzz]

I remember seeing that fire on TV which just reinforced my fear that I would never, ever, live in a high rise tower. But unfortunately some people have no choice for a variety of reasons.

Some people choose to, e.g. that build that is tilting in downtown San Franscico, or this 1400ft elegant mess in New York:
"Some of the billionaires at No 432 are now fighting with the developers — and each other — over myriad issues including millions of dollars in water damage from plumbing and mechanical faults, frequent lift malfunctions and walls that disconcertingly ‘creak like the galley of a ship’. The worst of the banging, groaning and clicking noises is produced by the communal rubbish chute that ‘sounds like a bomb’ when bags are dropped down it."
https://www.dailymail.co.uk/news/article-9225763/Residents-blighted-leaks-floods-tallest-residential-building-world.html
https://www.skyscrapercenter.com/building/432-park-avenue/13227

[Cerebus]

NW is "Navigation Wave" it's a expansion / extenstion of Long Wave to cover low frequency non-directional beacon transmitters. Akin to ADF on aircraft. It's used with a (in this case manual) directional loop antenna. Thi could be mouned on the bridge roof or for small craft, a hand-held ferrite "loopstick" on a cable.

Back in my youth I used to go sailing with my friend Paul on his father's small yacht. He had a device that looked a bit like a hand-held radar speed gun that received NW. You stood in the back of the boat and swept the thing around watching a signal strength reading from a meter on the back (optionally listening on a earpiece for a morse beacon ID) and when you'd got a signal peak amplitude lined up you took a bearing off the built in compass. Do this for two or three beacons and plot it on your charts and you knew, in theory, where you where.

[Robert763]

<SNIP>

Well that is certainly not what I expected as everyone seems to think 75 Ohm is inferior. Just a  thought, you're certain that the traces have not been incorrectly titled
[/quote]

In a coaxial system, all else being equal including shield ID, a 75R system has lower loss but 50R has higher power handling. Hence use of 50R for transmitting systems and 75R for Video, Cable TV receive antenna systems.
For long antenna runs the saving in line loss may be more than the mis-match loss. An example of this is the Trimble Thunderbolt GPSDO. The receiver and antenna are 50R but Trimble recommend using low loss 75R Cable TV coax.

[Robert763]

NW is "Navigation Wave" it's a expansion / extenstion of Long Wave to cover low frequency non-directional beacon transmitters. Akin to ADF on aircraft. It's used with a (in this case manual) directional loop antenna. Thi could be mouned on the bridge roof or for small craft, a hand-held ferrite "loopstick" on a cable.

Back in my youth I used to go sailing with my friend Paul on his father's small yacht. He had a device that looked a bit like a hand-held radar speed gun that received NW. You stood in the back of the boat and swept the thing around watching a signal strength reading from a meter on the back (optionally listening on a earpiece for a morse beacon ID) and when you'd got a signal peak amplitude lined up you took a bearing off the built in compass. Do this for two or three beacons and plot it on your charts and you knew, in theory, where you where.

Probably a SeaFix. I know he guy who made the injection molds for the plastics on those and most other Seafarer products.

[capt bullshot]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

I don't have a 75Ohm cable with a 50Ohm connector fitter (or vice versa), so I can't show that.
I've compared two BNC tees using a very simple (and non-calibrated) setup here. The VNA shows the "open" response, which ideally should be just a flat line at 0dB):

It's one of the "better" 50 Ohm cables (checked using the 1502 TDR), connected to an 50Ohm tee and a 75Ohm tee (by the looks, don't have any specs of them).
So the result isn't totally as expected, as the 50Ohm tee looks worse than the 75Ohm one hat higher (some GHz) frequencies. Normally, one would expect the 50Ohm one to look better in a 50Ohm setup

Comparing the tees at the TDR does judge the 75Ohm "better" than the 50Ohm tee in a 50Ohm setup, too ...

Two 75R "stubs" in parallel closer to 50R than two 50R in parallel?

Yes, that was what I guessed, too.
Using the TDR and the tee as a junction between two 50R cables (one stub left), the 50R tee shows a dip down to somewhat below 40R, while the 75R tee shows two bumps to about 60R with a dip to 50R between.
So yes, confirmed.

[capt bullshot]

To be honest a Time Domain Reflectometer (TDR) is better for spotting wrong impedance connectors and crimped cables than a basic VNA. VNAs don't natively show distance. The modern ones have a "Distance to Fault" function that provides a TDR like display by applying a FFT.

The Siglent has this function, indeed. Anyway, for short cables the TDR shows more useful results, providing finer distance resolution. Another difference: The 1502 TDR shows impedance over distance, while the Siglent basically shows return loss over distance.

[Cerebus]

NW is "Navigation Wave" it's a expansion / extenstion of Long Wave to cover low frequency non-directional beacon transmitters. Akin to ADF on aircraft. It's used with a (in this case manual) directional loop antenna. Thi could be mouned on the bridge roof or for small craft, a hand-held ferrite "loopstick" on a cable.

Back in my youth I used to go sailing with my friend Paul on his father's small yacht. He had a device that looked a bit like a hand-held radar speed gun that received NW. You stood in the back of the boat and swept the thing around watching a signal strength reading from a meter on the back (optionally listening on a earpiece for a morse beacon ID) and when you'd got a signal peak amplitude lined up you took a bearing off the built in compass. Do this for two or three beacons and plot it on your charts and you knew, in theory, where you where.

Probably a SeaFix. I know he guy who made the injection molds for the plastics on those and most other Seafarer products.

The name sounds plausible but I'm buggered if I can accurately remember the name on the box from all those years ago, we are talking about the first half of the 70s. I think I only saw the thing once when Paul hauled it out to demonstrate it to me in the harbour; I count being able to remember as much as I do, the principle of operation and the fact that it was in '73 or '74 as quite an achievement. 

[factory]

Sort of TEA related (has a voltmeter built in), I posted a pic of my shed radio (a Danish made Sailor 16T) a while ago and someone on here was interested in seeing inside it, well I've finally had enough of the voltmeter under-reading and decided to adjust it.

A quick teardown, this radio uses a lot of those Mullard/Philips AF11x series transistors that have a bad reputation of failing with tin-whisker related shorts, despite this I haven't had any trouble with them yet.



Here is the problem I have, with an external supply set for 9V I get a reading of approx 8V of the built in meter.

<BIG SNIP>

All back together with fresh set of 6 D sized leak-tubes. 


David

I have never before come across a radio which has NW on its dial and range switch, WTF is that then?

NW is "Navigation Wave" it's a expansion / extenstion of Long Wave to cover low frequency non-directional beacon transmitters. Akin to ADF on aircraft. It's used with a (in this case manual) directional loop antenna. Thi could be mouned on the bridge roof or for small craft, a hand-held ferrite "loopstick" on a cable.

Yes, I was about to post something similar.

The clue is the "D.F Aerial" on the NW range.

It actually has NW selections on the range switch for both the hi-impedance aerial & the D.F. aerial, of course I haven't got the D.F. aerial, probably got left in whatever this radio was removed from.



I do have a really crap low resolution picture of the advert from UK agent Coastal Radio Ltd, why I didn't look at it before posting as it's now very obvious that D.F. stands for direction finder. 


I'm also questioning if the circuit diagram is correct for my radio, it was found on the web years ago.

David

[factory]

Anyone want 2x HP 400E’s that require some work?

https://www.ebay.co.uk/itm/184674196350

Bit too modern for me, I tried & failed to win a 1960's 400E on ePay last week, it made £52 which seemed a lot considering it was grubby looking and had no feet.
https://www.ebay.co.uk/itm/133659380818

David

[bd139]

Anyone want 2x HP 400E’s that require some work?

https://www.ebay.co.uk/itm/184674196350

Bit too modern for me, I tried & failed to win a 1960's 400E on ePay last week, it made £52 which seemed a lot considering it was grubby looking and had no feet.
https://www.ebay.co.uk/itm/133659380818

David

yes that's a bit much for such an item. I'm not sure what has gotten into people to be honest. I'm going to stick with my 8060A for AF stuff and the Fluke RF probe for the higher frequency things I think.

I did think long and hard at what the failure mode is likely to be and I know the switching assembly on them and then the idea wore off  . If it was £20 the pair I'd just do it for the parts potentially but the seller I know won't take offers that are much lower than the offering price.

[med6753]

I remember seeing that fire on TV which just reinforced my fear that I would never, ever, live in a high rise tower. But unfortunately some people have no choice for a variety of reasons.

Some people choose to, e.g. that build that is tilting in downtown San Franscico, or this 1400ft elegant mess in New York:
"Some of the billionaires at No 432 are now fighting with the developers — and each other — over myriad issues including millions of dollars in water damage from plumbing and mechanical faults, frequent lift malfunctions and walls that disconcertingly ‘creak like the galley of a ship’. The worst of the banging, groaning and clicking noises is produced by the communal rubbish chute that ‘sounds like a bomb’ when bags are dropped down it."
https://www.dailymail.co.uk/news/article-9225763/Residents-blighted-leaks-floods-tallest-residential-building-world.html
https://www.skyscrapercenter.com/building/432-park-avenue/13227

On the other hand, I have absolutely no sympathy for them. 

[bd139]

Yeah fuck 'em 

On the subject of annoyances, I'm trying to build a VHF bandpass filter here at the moment and I've run out of bloody 0.65mm enamelled wire. Have resorted to unwinding power supply inductors from that old HP 1707B I had. The wire is annoyingly crusty though. Grr . I probably should just buy a roll.

(VHF bandpass is for the always unfinished spectrum analyser project first IF filter. Need 2MHz BW at 180MHz with really hard rolloff to at least -80dB at 30MHz either side. This turns out to be pretty hard without cavity filters and such)