EMRFD Message Archive 11554
Message Date From Subject 11554 2015-08-27 17:17:00 n1vc Another Spectrum Analyzer question
As I assemble my boards it is of course now time to think about enclosure and power supply. I am opting for the Hammond Aluminum diecast boxes for each component with of course feedthru capacitors. I am not concerned about the extra expense, but it should help with shielding. This brings up the subject of power supplies. The Aug 1998 article states the +15V supply supplies 0.5A and the -15V supply has much less demand. Although I have built receivers, I have never constructed a Spectrum analyzer and my gut feeling tells me to stay away from switchers. That is sad because the following switchers are only $9.95 and can supply up to 3A:
On the other hand here is a +15/-15V linear supply but it only supplies 0.4A at +15V. I think that might be marginal or insufficient for this app:
Of course I have the option to build a linear from scratch if I can dig up the correct center tapped transformer. I don't believe RS sells them anymore, and I have built enough of them in my day but may have thrown them away in the last purging of my basement...
Your comments/recommendations appreciated
11555 2015-08-27 19:07:24 John Lawson Re: Another Spectrum Analyzer question Hi Vince, Another option to consider........I built a homebrew power supply for my SA......I used a Radio Shack power transformer 273-1512 transformer that is still available on their website and a bridge rectifier from them too. I then purchased from Mouser the following regulators +15, -15, and a +12 volt, two 4700 uF caps and a cabinet. The remainder of the parts came from my junk box. I have found that the additi 11556 2015-08-27 20:38:08 firstname.lastname@example.org... Re: Another Spectrum Analyzer question
for my specan, i used a switching mode walwart. it does quiet fine. you just need careful bypassing everywhere inside the equipment. at times a guanella on the power line helps.
the important thing is to not have a common power line for your dvice under test and the analyzer. having small battery packs makes life easy and noise free.
a good ground if possible at all in the shack is yet another way to reduce line noise.
... most these are observations with a data point of one. i guess this is how lore starts.
11557 2015-08-27 21:43:20 Adrian Scripcă Re: Another Spectrum Analyzer question Hi Vince,As I started building the SA, I ran into the same problem: no 15V dual power supply so I stopped everything and started building the power source first. I used a 2x12V AC transformer for mine and it does well. 12V RMS x 1.414 translates to somewhere about 17V peak after rectification and after filtering I had enough voltage to use a pair of 7815/7915. Since I was going to use PCB for the SA modules, I thought I'd experiment with Manhattan building technique and use MeSquares.Here are some pictures of the power source I currently use to test the SA: https://goo.gl/photos/yzSKbqiRrQ4LuY4n7Don't mind the oversized bridge rectifier. It's the only one I had available.73Adrian, YO6SSW 11558 2015-08-28 01:39:53 Vaclav Peroutka Re: Another Spectrum Analyzer question Hi Adrian,
just one remark to your transformer. 230V tolerance is 10%, this means you can have 10.8V instead of 12V. Peak is then 15.3V, minus voltage drop on diode bridge = 14 Volts. 78xx-79xx need at least 2.5V more to maintain regulation. So you should not use 12V transformer even for powering 7812. If we go other direction - (15+2.5+1.3)/0.9/1.41 = 14.8Volts, this means that 2x15V AC transformer should be sufficient.
Beware of output capacitor on 79xx - this regulator is "LDO style" and needs at least 1uF. For 78xx, 100nF is ok.
---------- Původní zpráva ----------
Od: Adrian Scripcă email@example.com [emrfd]
Datum: 28. 8. 2015 6:43:25
Předmět: Re: [emrfd] Another Spectrum Analyzer questionHi Vince,As I started building the SA, I ran into the same problem: no 15V dual power supply so I stopped everything and started building the power source first. I used a 2x12V AC transformer for mine and it does well. 12V RMS x 1.414 translates to somewhere about 17V peak after rectification and after filtering I had enough voltage to use a pair of 7815/7915. Since I was going to use PCB for the SA modules, I thought I'd experiment with Manhattan building technique and use MeSquares.Here are some pictures of the power source I currently use to test the SA: https://goo.gl/photos/yzSKbqiRrQ4LuY4n7Don't mind the oversized bridge rectifier. It's the only one I had available.73Adrian, YO6SSW
11559 2015-08-28 08:16:49 Ed Manuel Re: Another Spectrum Analyzer question Vince,
One source of transformers these days is Frys Electronics (Frys.com). Search for Philmore in electronic components. There are a number of ckt boards and kits available. Google "bipolar power supply kit".
One, from Jameco is referenced here for $30 +shipping. http://tinyurl.com/4xvqvrk - even includes the transformer.
11560 2015-08-28 11:38:50 David J Nushardt Re: Another Spectrum Analyzer question
Hello,everyone, I been copying the mail about the W7ZOI SA with great interest, it's been on the back burner for years, seems like I have been waiting a life time for some enterprising individuals to make / offer the circuit boards again, I understand Bill with Kanga suffered a stroke, as I have myself Emrfd has kept me going and got me through some difficult times.
I'm still able to build circuits and pursue the hobby using the ugly method with my one good hand, although it has slowed me down considerably, it's a challenge but with patients it's do able.
I now have most parts, but the 5000 pf feed thru capacitors are expensive for me at 15.00 a pop through mouser or digikey, I would like to thank the individual who posted max gain as a source for good used feed thru's I placed a order for 30 @ .69 each are a steal!
They assured me max gain has enough to go around for all who are intrested, but order soon.
Hope to start building soon using the ugly method.
Sent from my Kindle fire HDX 8.9
11561 2015-08-28 13:02:00 nothdurftm Re: Another Spectrum Analyzer question Here's a nice cheap transformer that will give you dual 15 volt supplies and a 5 or 6 volt supply (diode drop will probably not allow a 9 volt supply).
Sam Woo Trans
Sam Woo transformer. 115 VAC input. Secondary #1- 9 VAC/1 amp. Secondary #2- 15 VAC/1 amp. Secondary #3- 15 VAC/500 mA. Dimensions: 3"x3"x3"
11562 2015-08-29 12:06:43 vasilyivanenko Re: Another Spectrum Analyzer question Another power supply option --- generate the negative DC voltage with A DC - DC converter. I've built
the time bases for a spectrum analyzer, sweeper etc. with my normal bench positive DC supply plus a DC-DC converter with a regulated negative DC voltage.
Here's a brief web showing some ideas + 1 link:
11564 2015-08-29 14:15:44 n1vc Re: Another Spectrum Analyzer question I appreciate the great response. I know have good number of paths to choose from
11568 2015-08-29 23:54:24 iam74@rocketmail.... Re: Another Spectrum Analyzer question Just one more...
Dave Johnson at DiscoverCircuits,com in his "Dave's Circuits" corner has exactly what you need: a +/- 15v supply using linear regulators and a single winding 20v transformer. With the Sam Woo transformer mentioned earlier, you could quite easily build a dual +/-6v, +/- 15v supply each supplying about 100-200 ma.
Or you could use the 15v and 9v windings in series to ensure a solid +/- 15v 500ma supply. It is easy to provide a current limiter with a single transistor at the output on each leg.
Hope this helps.