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Author Topic: RF signal generator  (Read 451 times)

KD2E

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RF signal generator
« on: February 03, 2022, 09:07:30 AM »

I have an HP 8640B, that I got when I worked for them.
It is old, and I expect could crap out whenever it wants to now.
Just like scopes and DVM's, I am wondering if there are more 'ham-friendly' options,
should I need to replace my 8640B.
Anyone have something new, and useable that they like and would recommend?
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W7CXC

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Re: RF signal generator
« Reply #1 on: February 03, 2022, 10:01:47 AM »

good question. My 8640b has the dreaded gear disease and have been wondering about the same question. There used to be a fellow that had a flat rate fix for that problem but have been unable to locate him. Will be very interested in the replies to your question.
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WB8VLC

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Re: RF signal generator
« Reply #2 on: February 03, 2022, 10:36:26 AM »

Same issue here, while my HP8640 still works fine I'm also planning ahead for when it stops working.

So I just picked up in a trade an excellent condition HP8920B  with a good working display, in return I installed an HF vertical with 60+  ground radials that I purchased myself along with trading of a good condition older kenwood HF transceiver and a power supply to a co-worker for  one of his spare HP8920B.

Since he had 3 of the HP8920's  the trade wasn't really an issue with him as he didn't have a problem with letting one good HP8920 go and I had pick of the litter, he was happy to get back on HF and he didn't have to do anything in the install and setup.
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G4AON

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Re: RF signal generator
« Reply #3 on: February 03, 2022, 11:24:23 AM »

I bought a new condition, military surplus IFR (Marconi Instruments) 2025. These signal generators are superb, covering 9 KHz to 2.51 GHz with output levels from -140 dBm to +25 dBm (with the high power option that mine has).

A good condition 2025 isn’t cheap, costing in the region of $1000 depending on options and warranty/calibration. There are also the 2023 and 2024 models with similar specs.

73 Dave
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K7LZR

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Re: RF signal generator
« Reply #4 on: February 03, 2022, 12:10:47 PM »

I've had several HP 8640B generators over the years and all of them worked but most developed various problems eventually. I did do the plastic gear repair on at least one of them I think. I later moved on to an HP 8656B which was a great generator albeit higher phase noise than the 8640B of course. I sold it due to needing something physically smaller and lighter.

For HF needs, I am currently using a GW Instek model AFG-2125 Arbitrary Function Generator. It will generate a very clean sinewave up to 25mhz, and AM, FM etc. modulation are available. Amplitude is accurate to within 1 dbm at 50Ω and I have verified this with a calibrated spectrum analyzer and also with an oscilloscope.

Its been a fantastic little generator and I'm pleased with it. Such generators are available with higher frequency ranges also.
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VK6HP

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Re: RF signal generator
« Reply #5 on: February 03, 2022, 04:11:27 PM »

I needed a signal generator with good phase noise performance but with tolerable construction complexity, and reasonable size and weight.  I looked closely at the IFR/Marconi range mentioned by Dave (G4AON, above) and would have been quite happy to own one of the models he mentions. However, other excellent performers, with slightly better phase noise, are the Rohde and Schwarz SML series and I was fortunate enough to find a pristine, ex military contractor, SML-01 with the pulse modulator and reverse power protection options fitted for AUD 800 (USD 560). Here's a data sheet:

https://www.testequipmenthq.com/datasheets/Rohde-Schwarz-SML01-Datasheet.pdf

One good feature is the fast and accurate electronic attenuator; stepped "sweep" functions are often less useful in ham environments than they appear by the time switching and settling specifications are accounted for but, with the fast frequency step and the electronic attenuator, I've found the SML-01 to be much more useful than e.g. a Rigol DSG815.  Like the Marconi generators the SML range also allows a "divider only" mode (pioneered by the HP8640B), which gives excellent phase noise over a very useful part of the frequency coverage.  Overall, the R&S unit shows a clean pair of heels to the old HP in overall phase noise terms.  (Still not as good as some of the later behemoth HP generators, which are fine instruments but weighty and not known for their reliability as they age).

One thing I liked about the IFR/Marconi generators is that more of the service information (to component level schematics) is in the public domain.  However, I judged that there was just about enough SML information around to make the trade-off between serviceability and phase noise swing towards the SML.  If you look at the failure points of the better HP and similar generators, mechanical attenuators are prominent, so well-designed electronic replacements are desirable.  (Bear in mind we are comparing low-GHz generators here; all bets are off if you decide you want a mm-wave synthesizer)!

73, Peter.
« Last Edit: February 03, 2022, 04:25:43 PM by VK6HP »
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KO4CFV

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Re: RF signal generator
« Reply #6 on: February 03, 2022, 04:27:25 PM »

I also own an HP 8640B. Regarding the delrin gears, there is a guy on ebay that sells brass replacements:

https://www.ebay.com/sch/i.html?_nkw=8640b+gears&_trksid=p2380057.m4084.l1313

Reasonably priced too..
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WA3SKN

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Re: RF signal generator
« Reply #7 on: February 05, 2022, 03:11:45 PM »

Gotta budget???
I love the old lab eqpt too, but the new eqpt costs are out of my ham budget range for most items.
Circuit Specialists does have some cost effective gear, and I can recommend the random wave generators, scopes, etc.
You will need to determine if their eqpt would meet your needs though.
73s.

-Mike.
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