DIY Spectrum Analyser
 

Here's an oddball - I discovered this in my loft. It's is absolutely something I will have made, but I don't remember what it is for!

The scanner and PSU boards are ones I recognise but I don't remember where from, but the RF bit is one I don't remember at all. It may be for the 35MHz or 459MHz model control bands....there's a 10MHz crystal on the RF board

Re: DIY Spectrum Analyser
 

Not wishing to insult you nor state the obvious, but since you seem to design and make a lot of your equipment, do you file the documentation for your finished items - or even those that are 'W-I-P', but never got completed? So perhaps you have that documentation filed away somewhere, but cannot remember where? Perhaps a good search in the attic or W-H-Y might be revealing. I say all that simply based on the way things get done here.
Just a thought.

Al. / May 10th.

Re: DIY Spectrum Analyser
 

It's not one of the cable TV types.

Is it the G4PMK one (Roger Blackwell) from Radcom?

David

Re: DIY Spectrum Analyser
 

Radcom G4PMK Spectrum Analyser November 1989.

The 10MHz crystal is for the marker generator.

Re: DIY Spectrum Analyser
 

Thanks everyone, it is indeed the G4PMK analyser. Now to see if it still works.....

Re: DIY Spectrum Analyser
 

If that crystal has three legs, it's likely to be a two-pole monolithic crystal filter used to do one of the resolution bandwidths. It's matched at each end by the two Toko IFTs. The wider IF bandwidth is done by the adjacent ceramic filter. The two blue doodads being relays to switch the filters. Running on old memories, the IF was 10.7MHz with bandwidths like 150kHz and 15kHz. The large silver lump with three screw heads on top is a Toko helical filter. I think it was a commonly used one intended for either the 2m or the 70cm amateur band, and used as the first IF in the dual-conversion up-converting receiver. Old memories 32 years past their sell by date, and the dear old RSGB made world radio heritage remove all old Radcoms....

David

Re: DIY Spectrum Analyser
 

You mean this one?

Peter

Re: DIY Spectrum Analyser
 

Aye, that one.

Incidentally the earlier DIY spectrum analyser that inspired Roger to get going was by Al Helfrick of Embry-Riddle Aviation University, better known for doing an excellent book on avionics, though it's getting a bit dated nowadays.

David

Re: DIY Spectrum Analyser
 

Yes, it has three legs and yes, it is the 10.7MHz filter, not a crystal. It was late when I took the lid off the box and I was both surprised and excited to find what was inside! Looking at it again this morning, it is exactly the SSA by Roger Blackwell.

I must have made more boards than I remembered, I sold a couple a few years ago. My business used to be involved in frequency scanning at model aircraft displays (health and safety!) so I remember we made a few specialised scanners for 27, 35 and 459MHz. We probably used the Blackwell design as a shortcut....

Re: DIY Spectrum Analyser
 

Mind what looks like a 75 Ohm BNC on the front panel.
Too easily busted by mating a 50 Ohm one. A silly idea we just have to live with, 2x impedances in same connector type.

Yours looks OK so far!

Re: DIY Spectrum Analyser
 

75 and 50 ohm BNC are physically compatible unlike N type which are not. The impedance difference in BNC is made by removing dialectric, the diameter of the pin is the same in each type.

I still have my G4PMK analyser, not that it gets much use these days.

Dave G3YMC