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Old 23rd Feb 2020, 6:48 pm   #1
Wendymott
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Default HF/VHF Signal generator revisited

Hi Peeps. As I have two spare DDS modules and controllers and a spare case I decided to revisit the HF/VHF Signal generator and add a couple of items... the previous version was quite basic, not having a good switched attenuator and Output Level meter.
The Level AF Signal generator case was ideal, although its a bit limited space front to back, I had to remove some internal metalwork.
Even though I had two of the modules, and the Relay switched attenuator, the other bits needed design and building.

Schematics are available if required

The BIG problem now is......... Whats next ??
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Old 23rd Feb 2020, 9:37 pm   #2
MrBungle
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Default Re: HF/VHF Signal generator revisited

Looking good. You need to build a W7ZOI spectrum analyser to check the output of your signal generator now

(Still haven’t finished mine after 2 years now)
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Old 24th Feb 2020, 1:56 pm   #3
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Question Re: HF/VHF Signal generator revisited

A well-constructed piece of test gear; looks professional: well done.

However, I'm a bit puzzled about the choice of the selection of the attenuator ranges. Obviously, I have no idea of the physical construction of the insides of the illustrated attenuator box, nor do I know your intended use of this sig. gen.

As for as the atten. switches chosen, attens. of -1, -4, -6 and -9 dB are not obtainable; I would have thought that -6 dB was especially desirable. For 6 switches, I would have chosen 1, 2, 4, 8, 16 and 32 dB, producing a max. atten of 63 dB with 1 dB steps.

Please don't take that as negative criticism: it's merely a thought based on observation.

Al.
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Old 24th Feb 2020, 3:13 pm   #4
Wendymott
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Default Re: HF/VHF Signal generator revisited

Hi Al. Thanks for your comments and observations ... I decided to omit the 1dB switch to add another 20dB. Its not intended as a Finite instrument.. rather an aid to developing receivers and such, where I need a substitute Local Oscillator, and also signals small enough so as not to swamp RF front ends. I have an Anritsu generator for the serious measurements. My previous offering from last year still stands, but is simpler, without Level meter and attenuator.

Mr Bungle....I had thought about "playing" with a Spectrum Analyser but my Siglent SAA 3000X could never be matched.

Just had a look at the W7ZOI item..... looks interesting...maybe good for a "Club" project..... but I find that a Tracking Generator is essential.... yes I know there are other ways, but its nice to be built in.

Here are the schematics of the current version..
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Old 24th Feb 2020, 3:24 pm   #5
Wendymott
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Default Re: HF/VHF Signal generator revisited

Just been re reading the W7ZOI article... its spread over a few issues etc.. I see it has a Tracking generator... sorry for my dismissal.
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Old 24th Feb 2020, 7:49 pm   #6
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Default Re: HF/VHF Signal generator revisited

Yes it has evolved somewhat over the years. There are also a ton of updates on W7ZOI’s web site as well. I’ll probably never finish mine
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Old 24th Feb 2020, 11:35 pm   #7
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Default Re: HF/VHF Signal generator revisited

A few years + ago, when I was working at a firm that produced gear for VHF band II transmitters, I regularly used an Anritsu spectrum analyser that lived on my test bench. That analyser had a tracking generator built in - and made measurements a lot easier than would have been the case without. Here, at home, I use an Advantest TR4132 S/A: it lacks a tracking gen. - and as such its usefulness it quite restricted in comparison, especially when it comes to determining bandwidth / freq. response of things like WBAs and filters, etc.

Al.
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Old 25th Feb 2020, 11:51 am   #8
Wendymott
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Default Re: HF/VHF Signal generator revisited

Ai... Apparently... if you have a noise generator... you can use that with the spectrum analyser to test filters etc.... never tried it... but I gather it is a substitute.
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Old 25th Feb 2020, 1:47 pm   #9
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Default Re: HF/VHF Signal generator revisited

Thanks Wendy - I can understand the general thinking embedded in using a noise generator for that purpose. Last time I used one of those was during professional employment in 1970 (approx. )
I have a few A2087 valves in stock that just might form the basis of such a tool.

One day . . . one day . . .

Al.
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