8th Jun 2017, 10:20 am | #41 |
Dekatron
Join Date: Jun 2016
Location: London, UK.
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Re: Spectrum Analyser
Nothing clever! Klunky: http://www.qsl.net/wd9eyb/klunky/framed.html ... microsoft paint and Debug4x (HP 50g emulator): http://www.debug4x.com/
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12th Jul 2017, 8:10 am | #42 |
Dekatron
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Re: Spectrum Analyser
Rest of the parts have arrived for mine finally! Now to find the time.
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12th Jul 2017, 9:27 am | #43 |
Hexode
Join Date: Jun 2005
Location: Aberystwyth, Wales, UK.
Posts: 358
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Re: Spectrum Analyser
Great, I look forward to seeing pictures of the completed instrument. I have added an audio out to mine and have wasted a lot of time scanning and listening to the short wave bands. I now have plans for something a little better that covers up to around 300MHz with better IF filters.
Dave GW7ONS |
31st Jul 2017, 12:21 am | #44 |
Dekatron
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Re: Spectrum Analyser
Excellent. Glad to hear progress. The audio output is an interesting idea. Technically it's a receiver so it makes sense!
Haven't had much time to proceed on mine due to work. I built another wildly unstable embarrassing attempt at a VCO and am currently scratching my head and cheating via looking at frequency synthesis techniques instead which have been so far scuppered by an iffy breadboard. I build a semi-successful PLL about a year ago which could be driven by a microcontroller. I can also persuade this to talk to the log amp on the output via an ADC. This can be chucked up and down a serial port for display on a PC. A cop out perhaps but it avoids all the linearity problems. Add another VCO/PLL suitably offset and you have a poor man's VNA! I will attempt to get it working in its analogue form first however before I attempt the above. 2 weeks of contract to go now and then 8 weeks of spare time |
18th Aug 2017, 4:01 pm | #45 |
Dekatron
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Re: Spectrum Analyser
Back again. Finally on holiday. Woohoo. After a couple of dead ends building PLLs that I couldn't get stable I went back to basics and I built a new sweep generator design today which requires just four discrete transistors (in a CA3096) and has good linearity. Currently dealing with temperature compensation, adding a follower, discrete summing differential amplifier (another CA3096) to change offset and a pot for span. Low tech wins. I'll detail this shortly when I've got it all working.
VCO is more stable now I have put it in a little PCB box and shortened some component leads. I think it needs more supply decoupling as well. Awaiting arrival of some feed-through capacitors for this. Also got some SMA connectors arriving from China in the next week or so. Then filter time. Unfortunately major spanner in the works: my scope blew up last week (looks like it's EOL for this one - multiple power supply components shot). Ergo I've had to borrow the only thing I can get my hands on, a Tek TDS210 with a dead B channel |
21st Aug 2017, 6:49 pm | #46 |
Hexode
Join Date: Jun 2005
Location: Aberystwyth, Wales, UK.
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Re: Spectrum Analyser
Sounds interesting, looking forward to seeing the details. I recently found a couple HPF-505X-1 mixers and have purchased a ready built VCO from ebay covering 515-1050MHz. I am thinking along the lines of a 0-500MHz spectrum analyser with a first IF of around 700MHz, a second IF of around 180MHz (or whatever the frequency of the helical filter I have) and a final IF of around 10.7MHz. The problem I will have is with local oscillator stability, I am just mulling the ideas over at the moment.
Dave GW7ONS |
21st Aug 2017, 7:14 pm | #47 |
Dekatron
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Re: Spectrum Analyser
That would be interesting. I think the impending strip line and impedance control magic would put me off things at that frequency. Would certainly be a nice bit of equipment when finished. LO stability is killing me on three projects I have on the go at the moment. It appears I lack the relevant black magic skills still. Working on it!
I have secured a new oscilloscope this morning (well actually two!) so after some playing it's back on the project. Annoyingly the SMA connectors turned up and they were some mixed LEDs (huh?) Chinese supplier generic packing failure. New ones being sent out today. |
27th Aug 2017, 3:27 pm | #48 |
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Re: Spectrum Analyser
After a few days of oscilloscope shenanigans I have a working non digital unit (I can't stand the things). VCO, sweep and log detector now operational. Decided to wire it up to a resonant circuit just to get something out of it.
So far so good. Awaiting some more SMA bits from RS on Wednesday so I can actually get further with this. Next thing is mixers and filters. |
3rd Sep 2017, 7:47 pm | #49 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Spectrum Analyser
Forgive my ignorance but this might be relevant to a project I might want to try, so was wondering about the construction of the board. It looks like just a plain copper clad PCB with all of the components tacked on to it? Are the common grounds just connected to the copper base while the legs remain floating in mid air? Or did you need to cut bits out with a sharp knife?
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3rd Sep 2017, 8:13 pm | #50 |
Hexode
Join Date: Jun 2005
Location: Aberystwyth, Wales, UK.
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Re: Spectrum Analyser
Hi WaveyDipole,
The integrated circuits had there legs bent 90 degrees and were soldered to pieces of veroboard that were glued to the pcb ground plane, the components were attached to pieces of copper clad board cut into small squares and glued to the pcb groundplane. I did not use this method of construction for the final analyser, for the rf side I used a single sided copperclad board as a groundplane and drilled holes for the components and connected them together with wire on the reverse side. I was not happy with this as it looks a bit untidy but it did work well. Dave GW7ONS |
3rd Sep 2017, 8:21 pm | #51 |
Hexode
Join Date: Jun 2005
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Re: Spectrum Analyser
Here is a link showing Manhattan construction: https://i0.wp.com/www.pbase.com/dave...7/original.jpg
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3rd Sep 2017, 9:02 pm | #52 |
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Re: Spectrum Analyser
Article here as well: http://www.aoc.nrao.edu/~pharden/hobby/HG-MANHAT1.pdf http://www.aoc.nrao.edu/~pharden/hobby/HG-MANHAT2.pdf
If you look at page 6/7 of the second PDF, that's how I'm building mine. |
3rd Sep 2017, 9:27 pm | #53 |
Hexode
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Re: Spectrum Analyser
Thanks for the link MrBungle, it explains the technique very well.
Dave GW7ONS |
3rd Sep 2017, 11:44 pm | #54 |
Octode
Join Date: Jan 2014
Location: Oban, Scotland, UK.
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Re: Spectrum Analyser
I've successfully used 0.2mm single sided copper board for 'landing pads' by using a hole punch to pop out dozens that glue quite nicely.
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4th Sep 2017, 8:48 am | #55 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Spectrum Analyser
Thanks for the explanation and links to the articles on the 'Manhattan' technique. These were very helpful and I have saved a copy of those PDFs. The image also shows clearly how the ICs are placed. Up until now, I have made use of only vero or strip board and occasionally breadboard for prototyping. These have been fine generally but I understand become problematic at higher frequencies. Since I'm considering building an RF sig gen which I am hoping will produce output up to 300MHz, or at the very least to cover FM, air and UHF frequencies, I was starting to think about how to tackle this problem. I have also been thinking about SA's although this would perhpas be a future project.
While reading these PDFs I did start wondering about how to cut pads since I do not have one of those nibbler tools. I do have a hole punch so maybe the 0.2mm board idea mentioned by kellys_eye idea would work, otherwise I guess it will be down to using a hacksaw. Is there a 'best' place to source the PCB board or just general suppliers like RS and Farnell? |
4th Sep 2017, 9:03 am | #56 |
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Re: Spectrum Analyser
RS sell some very nice really thin FR4 board although I will say it knackered my hole punch in about 5 minutes flat. I am using aviation shears with it (from machine mart). Don't try this with SRBP board - it just shatters and crumbles.
At 300Mhz things start getting difficult. Particularly if you want reproducibility of a design. Stray inductance and capacitance is trouble. Even the strips glued down act as small capacitors which are not very good so you have to factor those into the design (or just wire it point to point!) |
4th Sep 2017, 12:48 pm | #57 |
Nonode
Join Date: Mar 2013
Location: Leicester, UK
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Re: Spectrum Analyser
Yes I did wonder that as I typed the above as each pad forms a small capacitor with the ground plane. If the copper underneath were scraped away first before gluing down maybe that would help but I dare say would be a bit of a pain to do. Otherwise, as you say, point to point wiring would be the way to go. I was not even considering reproducibility as these would be one off projects unless I mess something up and have to start again. Appreciate your insight though.
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4th Sep 2017, 12:55 pm | #58 |
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Re: Spectrum Analyser
I tend to just ignore these factors to start with and get it working first in some capacity. There is definitely a large margin for error even if you do consider this. For example when I built the VCO above it was running way slower than I wanted it to, I assume because of a naff calculation and/or parasitic capacitance so I spent a few minutes adjusting the shape and position of the inductor to compensate. I had to replace a capacitor with another one as well because it was too large.
If you look at the picture of the simple receiver I built here: https://www.vintage-radio.net/forum/...d.php?t=139481 you will see the amount of "error" that went into selecting capacitors for the tuned parts of it by the sheer number of MLCC caps that are wedged in it to trim everything. And on top of that there are three trimmers to adjust it (2 on back of the polyvaricons and 1 on the input filter). That was about 30 minutes' work with a proper DDS bench signal generator and scope. I dread to think how you'd tune it up with old kit! |
5th Sep 2017, 3:59 am | #59 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,340
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Re: Spectrum Analyser
Diamond Ceramic tile hole drills are one way of cutting pads from copper board.
Not expensive. This is one example, they are available in quite a few different places: http://www.ebay.com.au/itm/10Pcs-Dia...gAAOSw2D1ZfxtP Terry (Mods - please delete if inappropriate) |
5th Sep 2017, 8:25 am | #60 |
Dekatron
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Re: Spectrum Analyser
Those are a good option. G-QRP club sell a similar thing: http://www.gqrp.com/sales.pdf (page 3)
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