Test Equipment Anonymous (TEA) group therapy thread

[bd139]

I'd swap them out for BNC. Bear in mind output of that is probably 75 ohms.

I'd grab or make a minimum loss pad to get it down to 50. Lose about 6dB but worth it for compatibility with everything else which is pretty much 50 ohms. See: https://www.maximintegrated.com/en/app-notes/index.mvp/id/972

[Specmaster]

Yes it is 75 ohms output impedance and as you rightly say, almost everything else is 50 ohms. How does the Leader fare in that dept as it uses banana sockets? 

[bd139]

It has wild and unpredictable output impedance. They are usually loosely coupled for signal injection rather than calibrated output. I am considering modifying it shortly to add a buffer (TIA) which will give a predictable 50 ohm output. However not sure I’ll need that. Most of the time it will be whacked in the antenna hole and used to adjust double tuned circuits by ear. Nothing particularly critical.

[Specmaster]

So, have I got this round the right way, if I swap out the sockets for BNC ones, to effect the MLP's, I connect the lead that is currently going to the centre pin of the co-ax socket to the centre connection of the BNC via a 43ohm resistor and also from that some pin I take a 86 or 87 ohm resistor to ground and I do that twice, once on the RF output socket and again on the sweep socket for scope? I doubt I'll ever need the Ext input connection so I'll leave that alone, but if I was make that into a BNC, just do the same again or reverse the resistors as its more likely to be coming from a 50 ohm in to a 75 ohm input impedance?

[bd139]

I’d stuff a 75 ohm BNC on the generator straight up and build the pad inside a Pomona box you plug into it. Then when you get something else 75 ohm it’ll be useable as well.

I’d ony do this to the RF out.

[GerryBags]

I have a couple of new 75 Ohm panel mount BNC's from Amphenol if you need one, Specmaster? They came in a joblot.

[Specmaster]

I’d stuff a 75 ohm BNC on the generator straight up and build the pad inside a Pomona box you plug into it. Then when you get something else 75 ohm it’ll be useable as well.

I’d ony do this to the RF out.

Still a little puzzled about this seeing as the only 50 ohm inputs I have are the TF930 and the HP1740A which is switchable between 50ohm and 1M, all the other scopes tend to be 1M and also of course the TF930 can also be switched between 1M and 50ohm. If IIRC the only time the 50ohm input on the 1740A gets mentioned really is on some specific calibration tests?

Also of course when using the signal generator for setting up radios, whats the impedance there when the terminations are more likely going via small crock clips?

[Specmaster]

I have a couple of new 75 Ohm panel mount BNC's from Amphenol if you need one, Specmaster? They came in a joblot.

thanks, I'll get back to you on this, I'll guided by bd139 on if I actually need to do this as he's more in to this more than I am as ham operator.

[tautech]

I’d stuff a 75 ohm BNC on the generator straight up and build the pad inside a Pomona box you plug into it. Then when you get something else 75 ohm it’ll be useable as well.

I’d ony do this to the RF out.

Still a little puzzled about this seeing as the only 50 ohm inputs I have are the TF930 and the HP1740A which is switchable between 50ohm and 1M, all the other scopes tend to be 1M and also of course the TF930 can also be switched between 1M and 50ohm. If IIRC the only time the 50ohm input on the 1740A gets mentioned really is on some specific calibration tests?

Also of course when using the signal generator for setting up radios, whats the impedance there when the terminations are more likely going via small crock clips?

There are probes that specify they must be terminated into 50 .
Without an internal 50  input you then need used a feed through.

[tggzzz]

Still a little puzzled about this seeing as the only 50 ohm inputs I have are the TF930 and the HP1740A which is switchable between 50ohm and 1M, all the other scopes tend to be 1M and also of course the TF930 can also be switched between 1M and 50ohm. If IIRC the only time the 50ohm input on the 1740A gets mentioned really is on some specific calibration tests?

The excellent "low" impedance Z0 "resistive divider" probes have to be terminated in 50ohms, as do other classes of probes.

Those are actually a higher input impedance than so-called "high" impedance *10 probes (when input capacitance is included), and have a much higher bandwidth. Examples: 1.5GHz HP10020A or 6GHz HP54006A.

[tggzzz]

Quick test run of the Leader 17A on the scope.

6.5MHz. Nice clean sines!

You need a spectrum analyser to determine that! Scopes are not known for their input linearity, and gross crap looks OK in the time domain.

[Specmaster]

I’d stuff a 75 ohm BNC on the generator straight up and build the pad inside a Pomona box you plug into it. Then when you get something else 75 ohm it’ll be useable as well.

I’d ony do this to the RF out.

Still a little puzzled about this seeing as the only 50 ohm inputs I have are the TF930 and the HP1740A which is switchable between 50ohm and 1M, all the other scopes tend to be 1M and also of course the TF930 can also be switched between 1M and 50ohm. If IIRC the only time the 50ohm input on the 1740A gets mentioned really is on some specific calibration tests?

Also of course when using the signal generator for setting up radios, whats the impedance there when the terminations are more likely going via small crock clips?

There are probes that specify they must be terminated into 50 .
Without an internal 50  input you then need used a feed through.

I'm only really looking at frequencies used in normal domestic broadcast radios, from 100KHz to 108MHz is this strictly necessary? It is only for aligning the IF's and the oscillator tuning to correct align stations on the dial?                                                                                                       

[Specmaster]

Still a little puzzled about this seeing as the only 50 ohm inputs I have are the TF930 and the HP1740A which is switchable between 50ohm and 1M, all the other scopes tend to be 1M and also of course the TF930 can also be switched between 1M and 50ohm. If IIRC the only time the 50ohm input on the 1740A gets mentioned really is on some specific calibration tests?

The excellent "low" impedance Z0 "resistive divider" probes have to be terminated in 50ohms, as do other classes of probes.

Those are actually a higher input impedance than so-called "high" impedance *10 probes (when input capacitance is included), and have a much higher bandwidth. Examples: 1.5GHz HP10020A or 6GHz HP54006A.

Why would I be attaching probes to a signal generator? I'm more likely am I not (unless I'm missing something) be using a a lead terminating in a BNC at one end and a pair croc clips at the other. The highest bandwidth scope I'll be using is 100MHz. I'm only using the signal generator for normal domestic radio broadcast radios between 100 KHz and 108MHz?

[BravoV]

Not test equipment though  , but in this case these are categorized as Test Component as these will be used for the GPSDO board. A Huber+Suhner outdoor GPS antenna and Rosenberger N type male connectors.

As I have ordered my TruePosition GPSDO this very day, I'm now in need of an antenna, too. All I can find are terribly cheap antennas for cars and a few for boats. I have no real idea, though, whether they work with this board.

Well, at the Trueposition GPDSO big thread here, there are success using small patch antenna.

I'm a noob too, lets alone RF things, from what I read at the datasheet, the Furuno GPS receiver can drive a 50 Ohm LNA/active antenna at 5V 20ma, as this is typical for GPS.

Some can get good signal using small antenna at window sill like bd139 does, while here, I don't that kind of luxury as at window even I protruded the antenna head out, its still blocked by the longer protruding roof and also lots of trees with dense leafs, and the best only at 2 or 3 satellites and unstable.

Keep me updated too as I want to learn from your experience.

[bd139]

Quick test run of the Leader 17A on the scope.

6.5MHz. Nice clean sines!

You need a spectrum analyser to determine that! Scopes are not known for their input linearity, and gross crap looks OK in the time domain.

Of course, which is why I need one, but you can usually see anything more than about 30dBc if you’re running 10-20% of the scope’s bandwidth however as they look pretty nasty.  Enough to do a “more LPF needed” tests on a TX for example. Also if you have a receiver you can use it and the S meter as a crude SA and tune the harmonics.

[Ero-Shan]

Well, at the Trueposition GPDSO big thread here, there are success using small patch antenna.

I'm a noob too, lets alone RF things, from what I read at the datasheet, the Furuno GPS receiver can drive a 50 Ohm LNA/active antenna at 5V 20ma, as this is typical for GPS.

Some can get good signal using small antenna at window sill like bd139 does, while here, I don't that kind of luxury as at window even I protruded the antenna head out, its still blocked by the longer protruding roof and also lots of trees with dense leafs, and the best only at 2 or 3 satellites and unstable.

I'll probably order one of those less than 10 € ones just for a test (until the thing arrives it should be warm enough to open a window). I'm going to have major problems finding a hole to the outside to stick the cable through.

Keep me updated too as I want to learn from your experience.

I read: Keep me updated too as I want to learn from your errors. 

[bd139]

I have a couple of new 75 Ohm panel mount BNC's from Amphenol if you need one, Specmaster? They came in a joblot.

thanks, I'll get back to you on this, I'll guided by bd139 on if I actually need to do this as he's more in to this more than I am as ham operator.

You don’t need this for aligning radios as you’re probably good enough just loosely coupling the generator to the antenna but it’s a convenience. The panel mount BNCs are on the mark though.

When i calibrate a receiver I’ve built i use a BNC patch with a 50 ohm through terminator plugged into the receiver’s antenna port. Either that or it’s perfectly acceptable to literally just stuff a bit of wire around the antenna and plug that into the generator. As long as you have gobs of the fundamental then you’re good.

There’s a surprising lack of science when it comes to RF sometimes

Edit: typical RX calibration for SSB/CW on 7Mhz.

1. Stuff a bit of wire in the antenna hole and into the generator
2. Set for 7.1MHz mid band, tune it and adjust front end filter for loudest signal.
3. Set for 7.2MHz top end of band, set VFO control to highest frequency, tune VFO centre for signal
4. Set for 7.0MHz bottom end of band, set VFO control to lowest frequency, tune VFO span for signal
5. Repeat 3/4 until it’s about right.
6. Loosely couple marker generator to antenna.
7. Set on 1MHz and tune VFO centre on low tuning again for 7.0MHz.
8. Set on 100KHz and draw the 100KHz marks on the dial
9. Set on 10KHz and draw the 10KHz marks on the dial

Sorted 

[BravoV]

I'll probably order one of those less than 10 € ones just for a test (until the thing arrives it should be warm enough to open a window). I'm going to have major problems finding a hole to the outside to stick the cable through.

Yeah, that is wise, I did the same testing using my friend's car GPS antenna, its just failed miserably and also its not designed to be truly outdoor antenna as mine will be placed high at/above roof level.

For sure I need to have it placed that high,and this change the simple antenna task into another beast compared to small & cheap at window's antenna, this is one of my potential -> Problem 

Hope your cheap solution works as planned.

I read: Keep me updated too as I want to learn from your errors. 

LOL ... 

[bd139]

Talking of GPS I think I (or my youngest) killed my QRP Labs GPS module. It's not responding now. Was sitting there on the window sill. There was a two hour opportunity where my youngest may have got at it but I couldn't see any finger prints on the board!

Haven't replied to any of the GPS antenna posts yet but have been reading them. I'm looking at permanent antenna options as well so this thread is interesting 

[BravoV]

Talking of GPS I think I (or my youngest) killed my QRP Labs GPS module. It's not responding now. Was sitting there on the window sill. There was a two hour opportunity where my youngest may have got at it but I couldn't see any finger prints on the board!

Wow  .. you put that bare board, powered & unprotected near the window for all this time ?

C'mon, get a cookies box or something and put that thing in there ...

[bd139]

Yep. I rarely end up with an enclosure around any of my projects. Only the GPS module has died. The generator works fine still. Might be something trivial.

[tautech]

Talking of GPS I think I (or my youngest) killed my QRP Labs GPS module. It's not responding now. Was sitting there on the window sill. There was a two hour opportunity where my youngest may have got at it but I couldn't see any finger prints on the board!

Haven't replied to any of the GPS antenna posts yet but have been reading them. I'm looking at permanent antenna options as well so this thread is interesting 

Oh c'mon, that's not fair blaming the kids ! The littlest one at that !

Or is penis fingers not wanting to own up ? 

[Specmaster]

I asked about all MLP and 75ohm sockets etc because I had already replaced the banana sockets on my Tech TE20D that I use for AM sets, over standard 50ohm sockets that I have in stick. It seems to work perfectly with and I get good sines from and on frequency as well. That sig gen will go upto 450MHz on harmonics the same as the Leader 17A. The Advance will only go to 230MHz and 7.5MHz at the other end so I need both sig gens. If the Tech did FM mod as well that's the one I'd keep.

From mobile device so predictive text might have struck again [emoji83]

[bd139]

Talking of GPS I think I (or my youngest) killed my QRP Labs GPS module. It's not responding now. Was sitting there on the window sill. There was a two hour opportunity where my youngest may have got at it but I couldn't see any finger prints on the board!

Haven't replied to any of the GPS antenna posts yet but have been reading them. I'm looking at permanent antenna options as well so this thread is interesting 

Oh c'mon, that's not fair blaming the kids ! The littlest one at that !

Or is penis fingers not wanting to own up ? 

The face and spit marks on the window next to it are a clue

Despite drinking half a keg the other day I don’t remember doing that.

[BravoV]

Talking of GPS I think I (or my youngest) killed my QRP Labs GPS module. It's not responding now. Was sitting there on the window sill. There was a two hour opportunity where my youngest may have got at it but I couldn't see any finger prints on the board!

Haven't replied to any of the GPS antenna posts yet but have been reading them. I'm looking at permanent antenna options as well so this thread is interesting 

Oh c'mon, that's not fair blaming the kids ! The littlest one at that !

Or is penis fingers not wanting to own up ? 

You just don't get it, its for the TEA excuse for SWMBO.