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Function Generator




 
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ka4koe
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« on: April 25, 2013, 10:50:51 AM »

Can anyone recommend a good make/model FG? Essentially I need audio up though at least 10 MHz for signal tracing porpoises. The other driver is "cheep", eg. used. I already have a Tek 465B/DM43 and an HP5327 counter, so a FG would be good to round out my test equipment.

tnx

Philip
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« Reply #1 on: April 25, 2013, 05:07:51 PM »


Under $50 you can get a DDS unit off ebay that does those jobs pretty well enough.
Not exactly the same as higher cost precision test gear, but quite useful. Various units have different features.

Worth a consideration.

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Jim, W5JO
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« Reply #2 on: April 25, 2013, 07:01:30 PM »

I found Solid State one at a fest that was made in Israel that worked to 10 meg and included a sweep function.  If you have never used a sweep generator and scope to align a radio, then you haven't lived.  Cost of the unit was about 10 bucks.
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ka4koe
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« Reply #3 on: April 25, 2013, 07:14:38 PM »

Well, my boatanchor total has exceeded 6, so its high time.
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MikeKE0ZUinkcmo
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« Reply #4 on: April 26, 2013, 06:57:12 AM »

I know there is often the hope that a function generator will produce two very different signal types, but they don't.   Function generators are NOT RF generators and classically don't have the stability or accuracy to be used as such, and as a audio generator they often have higher Sine wave distortion than a pure audio generator.   They also don't have means to provide a modulated output nor do they typically have suitable output attenuators.   They usually leak like crazy, so performing sensitivity tests are out of the question.

My suggestion is to purchase an audio Sine wave generator, good to a Meg or so, and a separate RF generator, with the old URM-25 or HP-606 as the bottom of the line.  These old work horses are stable and have what is needed to do basic RF testing and alignment.   

Sweep aligning of Comm receiver I.F. strips really doesn't buy you much unless you are purposely modifying or repairing the response curve of same, but it is cool to watch.   Lastly, I wouldn't consider the so called service or home built stuff at all, but, there are folks who are happy with that kind of thing.
 
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KM1H
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« Reply #5 on: April 27, 2013, 11:15:42 AM »

Yep, what Mike said except the specific models that are good are the URM 25D and up and the HP 606A and B.

I use a pair of 606A's for most LF-HF work altho I have a pair of HP 8640B's that are often unreliable and I use those strictly for VHF and up. The 606A's were easy to refurb and havent given a hint of trouble at around 10 and 5 years respectively. They are also easy to add a counter output and are even used with the HRO-500's I regularly overhaul.

The old workhorse URM-25D was then relegated to the auto radio and other simple stuff bench.

The service grade "instruments" from Heath, Eico, Knight, etc are completely useless for much beyond a S-38 which in itself is at the very bottom of the barrel with its peers.

Carl
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« Reply #6 on: April 27, 2013, 11:45:55 AM »

Carl and Mike provide sage advice Smiley  To add to that if you end up with an RF generator that doesn't go low enough to hit the 50-60 Khz. IF frequencies found in quite a few Hallicrafters, Hammarlund, and other receivers many audio oscillators will go high enough to use with those IF frequencies.

My HP-8640B doesn't go that low so for awhile I was using my HP-200 audio oscillator (goes up to 200 Khz.) for low IF frequencies when I didn't feel like dragging my HP-606A out.  A few years ago I acquired a HP low frequency converter that takes the 8640B down to 10 Khz.  I do have a spare 8640B but so far mine hasn't been troublesome-I probably don't put as many hours on mine as Carl does on his.

I agree with the others to stay away from the "service type" gear, the good stuff is far too cheap at hamfests not to use it.

If you end up with a non-digital readout generator most of the "lab type" gear has a high level output perfect for driving a counter.
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Rodger WQ9E
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« Reply #7 on: April 28, 2013, 02:06:23 PM »

The HP 11710B will extend the 8640B to 10KHz; Im surprised you didnt get in on that huge sale at Tucker and elsewhere when the USAF released a large number of NIB ones to surplus.

Carl
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« Reply #8 on: April 28, 2013, 03:32:07 PM »

The HP 11710B will extend the 8640B to 10KHz; Im surprised you didnt get in on that huge sale at Tucker and elsewhere when the USAF released a large number of NIB ones to surplus.

Carl

Mine wasn't from Tucker but it was one of the NIB units.  I bought some scope stuff from Tucker a long time ago but not after they decided to get in a race with SS of NE to see who could charge the most Smiley
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ka4koe
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« Reply #9 on: April 30, 2013, 04:06:15 PM »

I've love some version of a URM-25, but have you seen what folks are asking for them these days?
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MikeKE0ZUinkcmo
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« Reply #10 on: May 01, 2013, 07:08:57 AM »

If you wanna play you gotta pay Roll Eyes.   However, watch ebay on a DAILY BASIS, and you can eventually get one at a price you'll be willing to pay.   


Analyze the pics, note whats NOT said in the text, and ask sellers questions. 

Most ANY test gear you get, unless you have a pretty FAT wallet,  will be at least 30 years old, for digital gear, to as much as 60 years old, in the case of a urm25s or HP606s, so don't expect any guarantees other than "NOT DOA", but do expect the possibility of some repairs being required. 
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Mike KE0ZU

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ka4koe
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« Reply #11 on: May 01, 2013, 09:55:16 AM »

Those small one board cheapo jobs are looking better every day.

P
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WBear2GCR
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« Reply #12 on: May 06, 2013, 01:33:45 PM »

The ones that are cheap on ebay are DDS chips from AD, usually run by a PIC or Arduino or similar microprocessor.

As far as frequency range they go from somewhere around 1Hz up to their max range, and can be set to any frequency, one i have is good to 0.01Hz... the hitch is that the output is not a perfect waveshape in as much as it is from an D-->A converter and may have some stairstep in the output (a lowpass ought to fix that if needed).

But for general purpose use, I can't see how they would not be quite sufficient, and for "signal tracing" more than good. Cheap too.

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« Reply #13 on: May 06, 2013, 03:49:32 PM »

I have two HP 3325A function generators that I use often. 0 - 20MHz for sine wave and 0-10 MHz for triangle and square waves. It has an excellent programmable output level.

I use it as a VFO for all of my Long wave and Medium wave transmitters as it has the capability of an external 10 MHz reference. I use a Trimble Thunderbolt GPS to discipline all of my HP signal generators and counters. The HP 3325A is likely not the best for phase noise, but for my use, it fits the bill.

They can be picked up on EBAY for about $300 or so

Pat
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nq5t
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« Reply #14 on: May 07, 2013, 10:52:20 AM »

I have two HP 3325A function generators that I use often. 0 - 20MHz for sine wave and 0-10 MHz for triangle and square waves. It has an excellent programmable output level.



I second that.  I mostly use mine in sweep mode for IF strips, etc.  Useful to have around. 
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MikeKE0ZUinkcmo
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« Reply #15 on: May 09, 2013, 05:03:32 PM »

I use a HP-3336C mostly for sweeping, but it is a very accurate freq generator.  Sine only, accurate output level, and needs external attenuators to get below -72dbm, but handy nonetheless.

Those single board synthesizers are about as basic as you can get.   No Power, No Modulation, No Attenuator, lotsa harmonics....   I'd advise you save your money for the right piece of equipment.   
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Mike KE0ZU

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