Alignment Advice.

[Joe]

We're Stephensons as opposed to Brunels; though there's a streak of Oliver Bulleid in me too.

- Joe

[PyrusBoy]

I'll agree with that, I owed the Mid Norfolk Light railway for a while, and built 71/4 gauge locos. As a side shoot I have several first addition books on the formation of the railways.

[pwdrive]

Perhaps I'm missing something, (not unusual), but that 'Advance' pad / dummy aerial combo. confuses the hell out of me.

Why is the input terminal, that is connected to a generator whose source impedance is 75 Ω, labelled 37 Ω? I did some sums: assuming that the load on the DA and E output terminals is a very high impedance (which, itself, may not necessarily be so), the impedance that the generator 'sees' looking into the "37 Ω" socket is 75 Ω - as it should be, to match the generator's source impedance.* On that basis, that "37 Ω" input socket should be labelled "S.G. input: 75 Ω". Then everyone will understand that that socket should be joined to a generator of that impedance through a co-ax. cable whose impedance is also 75 Ω . . . . which is what is required and what 'Advance' clearly state is necessary and what their 'box' is designed to do.

* Moreover, that calculation of 75 Ω justifies the assumption that the load on the DA and E terminals is a very high impedance, otherwise that 75 Ω figure would be smaller).

Anyone care to enlighten my darkness, please?

Al.

Hi Al, maybe they are taking it to it's literal ie: 75r source & 75r load so two resistive impedances in parallel = 37r (actually 37.5r)....Maybe? It is confusing though, as you say "75r in" would make more sense.

Lawrence

[Joe]

Back On Topic, when I get the bits I think I can build one of these in a sardine tin.

- Joe

[Skywave]

Hi Al. maybe they are taking it too it's literal i.e.: 75r source & 75r load so two resistive impedances in parallel = 37r (actually 37.5r)....Maybe?
It is confusing though, as you say "75r in" would make more sense.

Lawrence

Yes, for one very generous moment, that thought did cross my mind - then I thought again. Since the 'box' is an external device and will have an Zin of 75 Ω 'looking into it' from the gen., then it should be labelled "75 Ω" - as I stated in my post to which you refer. If I picked that adapter up, I would go looking for a generator that had a Zout of 37.5 Ω.

Al.

[pwdrive]

I agree Al, it is missleading to me.

Lawrence.

[Skywave]

Hi, Joe,
Maybe your approach is much like mine, I make things work, I don't always understand or want to understand the theory. I have always been a practical type of engineer.

Up to a point, I agree. Indeed, there are times when I struggle with theory - but I'll always make an effort to understand it, simply because that although you can make / repair / test something by a trial-and-error method, if you have a good grasp of the theory - especially the fundamentals - then that can save yourself (and if acting professionally, your employer) a great deal of time (and possibly destroyed components ) when you are designing, testing or repairing something.
On the other hand I too have met and worked with highly-qualified engineers who seem to overlook the practicalities of implementing an idea. It is my humble opinion that an 'engineer' has a balanced blend of both sets of attributes.

Al.

[Skywave]

Back On Topic, when I get the bits I think I can build one of these in a sardine tin.
- Joe

Presumably you mean an empty one: you don't want the RSPCS* on your back!

* The Royal Society for the Prevention of Cruelty to Sardines

Al.

[pwdrive]

Something fishy goin' on here.

Lawrence.

[Joe]

I've made a TP1, as detailed in Post 10.

   

The only problem I had was finding that the sardine 'tin' was actually aluminium so couldn't be soldered. The top is therefore held on with epoxy and has bonding wires.

- Joe