Review of HP 8780A 3 GHz Vector generator (37 years too late) - Page 1
Forum section: electronics / testgear

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: October 16, 2024, 07:48:47 pm
content: I recently discovered HP 8780A generator, one of the first vector generators made by HP, that is still in many ways more powerful than modern ones, but has not been discussed here before. It has several unique modulation capabilities and can be found for less than $200, roughly one thousandth of its original price. It generates a signal near 10 GHz and then mixes it down, allowing for wide frequency and amplitude modulation.Here are a few examples of its capability:Wide vector modulation bandwidth >300 MHz. Uniquely, it has a parallel interface for clockless digital vector modulation in addition to analog vector modulation.Wide frequency modulation up to 250 MHz pp, even at low frequency. For example, frequency can be changed quickly by a factor of 6, from 10 to 60 MHz.Simultaneous frequency, phase, scalar amplitude, vector amplitude and burst modulation, if one desires.Here are some example screen shots:Vector amplitude modulation at 300 MHz of a 600 MHz signal. For comparison, also 30 MHz modulation of a 60 MHz signal is shown.Frequency modulation from 10 to 60 MHz and from 77 to 322 MHz, measured with HP modulation domain analyzer.Burst modulation of 1 GHz signal at 100 MHz.Measurements of burst extinction ratio. Here it is a little weak with only 50 dB extinction and some transient tail. The main signal is 500 mVrms here.The generator also has additional hidden features with "special" commands. It survived until Agilent days, there are application notes summarizing its capabilities. It is a good option for a low-cost "agile" signal source, while new ones from Keysight still cost 1000 times more.

author: Evergreen64
author_rank: Newbie
timestamp: October 16, 2024, 09:56:33 pm
content: "for under$200" Did you mean for under $2000? I did a little searching on the internet just now and I did find one on eBay for $225 (For Parts Only). The one that was listed as used but functioning was $2700.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: October 16, 2024, 10:50:08 pm
content: Look at the history of sales (available under Sell -> Research on ebay). I recently bought one for less than $200 (not counting shipping) and there were some even with free shipping in that price range.

author: rfclown
author_rank: Frequent Contributor
timestamp: October 17, 2024, 01:32:02 am
content: Ah, the memories. I used one in the late 80s. Top right in picture. The fans blew out the front bottom, and I remember the hot air blowing down on me the way I had it up on my bench riser. I used IOtech DAC to drive the IQ. Nice having built in arbs in the ESGs I have now. I think that was a two man lift device (I mean two person lift). I was surprised when I read the specs on the phase modulation input. It was REALLY low bandwidth (if I'm remembering this all correctly). I asked HP and was told it was put in for some customer who had some sort of phase tracking application.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: October 17, 2024, 03:59:37 am
content: It is a classic boat anchor for sure. The phase modulation option seems to have appeared later. It has a bandwidth greater than 10 MHz, but the maximum deviation is only a few radians, smaller than in newer signal generators.

author: KE5FX
author_rank: Super Contributor
timestamp: October 17, 2024, 03:33:15 pm
content: Interesting box, never encountered one before. Why does it need a separate phase modulation option? That's kind of the idea behind vector signal generators (well, half the idea, anyway.)

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: October 17, 2024, 04:50:20 pm
content: It mentions something about satellite communication as the application. One can imagine using phase control to rotate the pattern of digital vector modulation.

author: ttelectronic
author_rank: Regular Contributor
timestamp: October 17, 2024, 10:50:37 pm
content: Better late then never!I must admit if I found one in country and for that price, I would have a hard time not jumping on it...