Homebrew Radcom 1989 spectrum analyser find - UK Vintage Radio Repair and Restoration Discussion Forum

MrBungle · 29th Aug 2020, 8:05 pm

Hi all.

Been inactive here for a bit due to a number of things going on in my life (new job, covid, marital carnage and another forum I'm sure a few people here frequent and may know me from) but am sort of back again now.

Tripped over this glorious bit of kit on ebay a couple of weeks ago and this sort of fitted in with my homebrew spectrum analyser aspirations a couple of years back here as referenced in ParcGwyn's excellent thread: https://www.vintage-radio.net/forum/...d.php?t=135370 . As always, I got nowhere with the project because of various other commitments so I was relieved when what turned up was not a risky 30 quid carcass I'd paid for but an actual working Radcom spectrum analyser! No evidence it was that from the outside but googling the ICs in it lead to the original PDF here

Well I say working but there was a minor issue where the calibration oscillator had a dead 74LS90 in it. I replaced that and it seems to work absolutely fine. I've only brought it up on a bench supply for now as I didn't want to risk the mains filter exploding (new one on order).

What arrived. Minus the lid already which was off almost 3 seconds after the box was opened.

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Insides. Nicely constructed.

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Test rig

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Calibration output

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I don't have an analogue scope at the moment and neither of my digital ones are all that good for X-Y mode so I'll have to correct that at some point (I'll lurk for an HM203 or something) but I was rather chuffed. I'm awaiting a new mains filter and I will attempt to test and calibrate it past this.

There's a short video I recorded here of changing the centre frequency, calibration generator from 10 -> 1MHz and the bandwidth switch:

https://www.youtube.com/watch?v=hCnQ_e7AKBM

If anyone trips over this and knows who constructed it or recognises it or even if it has passed your hand I'd be interested. It was apparently from a house clearance so I suspect there is a sad story somewhere

Mooly · 29th Aug 2020, 8:28 pm

That brings back memories. Look what I have in a cupboard...

I used mine for VCR service/setup work on occasion and I remember buying the basic kit at the NARSA rally at Norbreck in Blackpool.

Mine went up in smoke last time I used it which must erm... 10 years or more back. A tant on one of the rails had expired.

Happy memories. Geez, I must have been keen back then

mole42uk · 30th Aug 2020, 6:45 am

I made the PCB’s for that years ago, used the power supply & sweeper boards trying for a 459MHz analyser. Gave up on that when I stopped working with such high frequencies.

Philips210 · 30th Aug 2020, 6:26 pm

Hi.

I built mine back in 2007 which was left untested for many years. I finally got around to testing it in 2018, see this thread https://www.vintage-radio.net/forum/...=135370&page=5 post #91

I think there must have been two versions of this spectrum analyser as the component layouts seem to be different particularly in the case of the RF board. A great project to build.

Regards,
Symon

Philips210 · 30th Aug 2020, 6:51 pm

Quote:

Originally Posted by MrBungle

I've only brought it up on a bench supply for now as I didn't want to risk the mains filter exploding (new one on order)

Hi.

When I built mine I could have used a combined IEC inlet filter but thought about any paper class X caps inside the can. I think these are potentially quite dangerous items if of a 'certain' make (no prizes for guessing the answer to that one!). I decided to build a separate filter and used suitable safety caps so hopefully much safer.

Regards,
Symon

MrBungle · 30th Aug 2020, 9:09 pm

Thanks all for the replies.

@Philips210: nice build. Tidier than this one! Mine seems to match the original article. I don't know if there was addendum or modifications after that article. As for the mains filter, indeed. I had one blow up on me a few years back which ruined the curry I was eating at the time!

@Mooly: also very nice build. I love seeing things that people have made.

I'm actually quite surprised at how good this thing is. The IF bandwidth is, well quite frankly miserable at 15KHz but it's fine for tuning up filters and looking at mixer products and harmonics. Not going to get anywhere near an HP crate with it of course. Once I've replaced the mains filter and obtained an analogue scope I'll calibrate it and do some further experiments with it.

ParcGwyn · 30th Aug 2020, 10:22 pm

What a nice bit of kit, the shape of the 15kHz filter is very poor using the components specified in the original design. I originally thought I had a defective component. Looking at past articles on the analyser there appeared to be 2 designs for the PCB, the original and ones supplied by Jabdog.

Dave
GW7ONS

MrBungle · 30th Aug 2020, 10:57 pm

Yes it’s not great. There’s a double peak in it from what I can see. This may be the alignment however in my case as the 15khz filter is sandwiched between two IF cans by the looks. Will find out and write it up.

I built a noise generator this evening so I can throw a filter at it. Obviously a nice flat tracking generator would be nice but that’s not happening but it’s fairly flat across a typical filter - enough to make useful measurements with anyway.

MrBungle · 1st Sep 2020, 10:46 pm

Mains filter replaced today and fully working. Managed to grab an "untested but displays stuff" Hameg HM203-5 off ebay today which will serve as a display for it (assuming it's not a lemon!). Scope will also work for my in development curve tracer

William78 · 2nd Sep 2020, 5:59 pm

I also build the Radcom Simple Spectrum Analyser using a kit of parts from Jabdog about seven years ago.
I think the most interesting bit was understanding how it works, rather than just assembling the kit and switching on. Also I have yet to finish the front panel properly, a common failure for me.

A few photos,

Inside

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The Rf board

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In use on full sweep, Mw stations on the left of the display and some band 2 stations on the right at around 90 MHz

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William

IanG3XYV · 2nd Sep 2020, 9:18 pm

I built up a kit of parts in the 90s. Worked very well as a breadboard I recall but never got round to housing it properly. Still have the bits. Drop me a line if anyone is interested.

Ian

MrBungle · 3rd Sep 2020, 12:54 pm

Very interested in this. I will PM you

Replying to William78 - another nice build there! This appears to have been quite a popular project based on the number of examples appearing in here.

Got my Hameg today. Needed a bit of a clean up and a small repair but it works fine. Can't really take a decent photo of it with this phone unfortunately:

29th Aug 2020, 8:05 pm	#1
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Homebrew Radcom 1989 spectrum analyser find Hi all. Been inactive here for a bit due to a number of things going on in my life (new job, covid, marital carnage and another forum I'm sure a few people here frequent and may know me from) but am sort of back again now. Tripped over this glorious bit of kit on ebay a couple of weeks ago and this sort of fitted in with my homebrew spectrum analyser aspirations a couple of years back here as referenced in ParcGwyn's excellent thread: https://www.vintage-radio.net/forum/...d.php?t=135370 . As always, I got nowhere with the project because of various other commitments so I was relieved when what turned up was not a risky 30 quid carcass I'd paid for but an actual working Radcom spectrum analyser! No evidence it was that from the outside but googling the ICs in it lead to the original PDF here Well I say working but there was a minor issue where the calibration oscillator had a dead 74LS90 in it. I replaced that and it seems to work absolutely fine. I've only brought it up on a bench supply for now as I didn't want to risk the mains filter exploding (new one on order). What arrived. Minus the lid already which was off almost 3 seconds after the box was opened. Insides. Nicely constructed. Test rig Calibration output I don't have an analogue scope at the moment and neither of my digital ones are all that good for X-Y mode so I'll have to correct that at some point (I'll lurk for an HM203 or something) but I was rather chuffed. I'm awaiting a new mains filter and I will attempt to test and calibrate it past this. There's a short video I recorded here of changing the centre frequency, calibration generator from 10 -> 1MHz and the bandwidth switch: https://www.youtube.com/watch?v=hCnQ_e7AKBM If anyone trips over this and knows who constructed it or recognises it or even if it has passed your hand I'd be interested. It was apparently from a house clearance so I suspect there is a sad story somewhere

29th Aug 2020, 8:28 pm	#2
Mooly Octode Join Date: May 2011 Location: Lancashire, UK. Posts: 1,351	Re: Homebrew Radcom 1989 spectrum analyser find That brings back memories. Look what I have in a cupboard... I used mine for VCR service/setup work on occasion and I remember buying the basic kit at the NARSA rally at Norbreck in Blackpool. Mine went up in smoke last time I used it which must erm... 10 years or more back. A tant on one of the rails had expired. Happy memories. Geez, I must have been keen back then Attached Thumbnails

30th Aug 2020, 6:45 am	#3
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,608	Re: Homebrew Radcom 1989 spectrum analyser find I made the PCB’s for that years ago, used the power supply & sweeper boards trying for a 459MHz analyser. Gave up on that when I stopped working with such high frequencies. __________________ Richard Index: recursive loop: see recursive loop

30th Aug 2020, 6:26 pm	#4
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,573	Re: Homebrew Radcom 1989 spectrum analyser find Hi. I built mine back in 2007 which was left untested for many years. I finally got around to testing it in 2018, see this thread https://www.vintage-radio.net/forum/...=135370&page=5 post #91 I think there must have been two versions of this spectrum analyser as the component layouts seem to be different particularly in the case of the RF board. A great project to build. Regards, Symon

30th Aug 2020, 9:09 pm	#6
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Homebrew Radcom 1989 spectrum analyser find Thanks all for the replies. @Philips210: nice build. Tidier than this one! Mine seems to match the original article. I don't know if there was addendum or modifications after that article. As for the mains filter, indeed. I had one blow up on me a few years back which ruined the curry I was eating at the time! @Mooly: also very nice build. I love seeing things that people have made. I'm actually quite surprised at how good this thing is. The IF bandwidth is, well quite frankly miserable at 15KHz but it's fine for tuning up filters and looking at mixer products and harmonics. Not going to get anywhere near an HP crate with it of course. Once I've replaced the mains filter and obtained an analogue scope I'll calibrate it and do some further experiments with it.

30th Aug 2020, 10:22 pm	#7
ParcGwyn Hexode Join Date: Jun 2005 Location: Aberystwyth, Wales, UK. Posts: 358	Re: Homebrew Radcom 1989 spectrum analyser find What a nice bit of kit, the shape of the 15kHz filter is very poor using the components specified in the original design. I originally thought I had a defective component. Looking at past articles on the analyser there appeared to be 2 designs for the PCB, the original and ones supplied by Jabdog. Dave GW7ONS

30th Aug 2020, 10:57 pm	#8
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Homebrew Radcom 1989 spectrum analyser find Yes it’s not great. There’s a double peak in it from what I can see. This may be the alignment however in my case as the 15khz filter is sandwiched between two IF cans by the looks. Will find out and write it up. I built a noise generator this evening so I can throw a filter at it. Obviously a nice flat tracking generator would be nice but that’s not happening but it’s fairly flat across a typical filter - enough to make useful measurements with anyway.

1st Sep 2020, 10:46 pm	#9
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Homebrew Radcom 1989 spectrum analyser find Mains filter replaced today and fully working. Managed to grab an "untested but displays stuff" Hameg HM203-5 off ebay today which will serve as a display for it (assuming it's not a lemon!). Scope will also work for my in development curve tracer

2nd Sep 2020, 5:59 pm	#10
William78 Triode Join Date: Oct 2007 Location: Warrington, Cheshire, UK. Posts: 25	Re: Homebrew Radcom 1989 spectrum analyser find I also build the Radcom Simple Spectrum Analyser using a kit of parts from Jabdog about seven years ago. I think the most interesting bit was understanding how it works, rather than just assembling the kit and switching on. Also I have yet to finish the front panel properly, a common failure for me. A few photos, Inside The Rf board In use on full sweep, Mw stations on the left of the display and some band 2 stations on the right at around 90 MHz William

2nd Sep 2020, 9:18 pm	#11
IanG3XYV Pentode Join Date: Sep 2014 Location: Bedford, Bedfordshire, UK. Posts: 174	Re: Homebrew Radcom 1989 spectrum analyser find I built up a kit of parts in the 90s. Worked very well as a breadboard I recall but never got round to housing it properly. Still have the bits. Drop me a line if anyone is interested. Ian

3rd Sep 2020, 12:54 pm	#12
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: Homebrew Radcom 1989 spectrum analyser find Very interested in this. I will PM you Replying to William78 - another nice build there! This appears to have been quite a popular project based on the number of examples appearing in here. Got my Hameg today. Needed a bit of a clean up and a small repair but it works fine. Can't really take a decent photo of it with this phone unfortunately: Attached Thumbnails Last edited by MrBungle; 3rd Sep 2020 at 1:10 pm.