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Author Topic: Leader LSG-17 Signal Generator?  (Read 5977 times)
N0URE
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Posts: 42




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« on: October 08, 2011, 02:12:29 PM »

Anyone have a manual?
Anything good or bad about these as a used purchase?

73 John TI4/N0URE
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VK2TIL
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Posts: 332




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« Reply #1 on: October 08, 2011, 11:40:11 PM »

I think that the '17 is substantially the same as a '16, just a "face-lifted" model; there is an LSG-16 manual on BAMA.

http://bama.edebris.com/manuals/leader/lsg16/

This kind of instrument is not a "serious" signal generator; they drift in frequency, they leak signal and they do not have a good output attenuator (nor is the output impedance 50-ohms).

Whilst the LSG-16 has a co-axial Motorola output connector the LSG-17 has banana-post output terminals; not the sign of a "serious" signal generator.

I have a '16; I bought it for a few $$$s because it was cute and because I thought it might be a useful "VFO" for experiments with mixers and receivers.  I only had one good signal generator (Rohde & Scwartz SMS) at the time and two generators are useful for such work.

I built an output amplifier to give a 50-ohm output impedance; that was useful but the drift and the RF leaks still remained.  I haven't used it for a long time.

I later built a DDS kit ( http://www.minikits.com.au/kits5.html ) and put it in a metal box; I replaced the MMIC output amplifier with a discrete-transistor one to reduce the harmonics and this works quite well.  I set the output at +10 dBm to use with mixers that require either that drive level or a drive level of +7 dBm when a simple 3 dB attenuator does the job.

Still later I "bit the bullet" and bought a HP8657B so I now have two good signal generators but I still use the DDS one sometimes as it's quite small on the bench and I sometimes find a tuning knob more convenient than a push-button.

I wouldn't pay a lot for the LSG-17; if it's going for $20 or so it might be fun to play with but I wouldn't pay serious money for it.
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N0URE
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Posts: 42




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« Reply #2 on: October 09, 2011, 08:48:59 AM »

Kerry,

thank you for your informative comments. I too have a DDS unit on order.
I am not doing any design work so the HP is above my budget and my K2 is out for repair.
Do you know, is your LGS-16  600 ohm impedance?
My current need is only to set Image Rejection on SoftRock and Genesis G59. I may
set a low limit on my Ebay auto bid.

Thanks again for your comments.

73 John TI4/N0URE

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VK2TIL
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Posts: 332




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« Reply #3 on: October 09, 2011, 01:54:43 PM »

The output impedance of the '16 is variable as can be seen from the schematic;



The output passes through a pot and some resistors so it will depend on where the pot is set; it is certainly not a constant figure.  The output is also fairly low in power so there is little opportunity to set a 50-ohm or other impedance with attenuation.

I added an output amplifier;



As I recall this gave +14dBm output so I added 4dB of attenuation to give an output of +10dBm at the generator output connector; the amp output was already around 50 ohms and the attenuator helped fix it at that.

If you require 600 ohms impedance (more audio than RF usually) you can just put 550 ohms in series with a "standard" 50-ohm output.

It was an interesting exercise but it didn't really result in a good generator; the DDS one is much better;





I found that much of the harmonics in the output was due to the MMIC final amp rather than the DDS system so I replaced the MMIC with an amp similar to the one I used in the Leader; it's probably capable of +25dBm output so it  "loafs" in this service and is very linear and clean.

Used with external attenuation if required it makes a nice small generator for the bench; as I said, a tuning knob is often much more convenient than a push-button and a small instrument on the bench can save constantly reaching up to a shelf to push a button on a large instrument.

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VK2TIL
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Posts: 332




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« Reply #4 on: October 10, 2011, 01:55:01 AM »

Just a note to say that I was wrong about my Leader signal generator; it's an LSG-15, not a '16.



Well; I said that I hadn't used it for some time!  Smiley

I think that the '15, the '16 and the '17 are all essentially the same; the later ones are just "face-lifted" '15s.





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