Comments wanted regarding the HP 8656B

[N6YW]

Greetings to all
I am considering buying a better RF signal generator and have found several people I know own
and operate this machine, the Agilent HP 8656B. I have never used one and know nothing about them
other than what I have heard. George, W1LSB uses one and it gave me the idea to look into this
model. I am looking for comments and or suggestions that either point to this one or something better
in the same price range, around 500 bucks max.
I thank you all in advance.
73 de Billy N6YW

[W4AMV]

I have three and use them for IM measurements. Their phase noise is good, not great (i.e. as good as the 8640). However, their frequency range is greater and quality is up to par with HP/Agilent as you know. Take care in the one you purchase... Several years ago HP had an "oops" event and was shipping the 56 with the LINE VOLTAGE directly TIED TO THE FAN . So the FAN operated all the time!

73'

[flintstone mop]

I swear that the HP unit comes so close to the Marconi 2019. There is one on eBay BTW.
Front panel layout.

I kinda regret the purchase I made for the Marconi.
Fred

[N4LTA]

I have one and use it often. I would be in bad shape without it.

Pat

[N6YW]

Having never owned a really good generator, this model looks to be more than adequate to provide
meaningful and accurate results. My current generator is a BK Precision, and is anything but precision.
These seem to be a fairly good bargain in the range of 400-800 dollars depending on where you purchase one.
The tricky part, is buying one that doesn't have problems or is on the verge.
Can anyone give some advice on how to properly purchase one? What to look for and which options are
really needed?
Thanks again for your comments.
73 de Billy N6YW

[flintstone mop]

During my searching, the more you want guarantees and that the instrument is calibrated the higher the cost, even on ePay.
You take your chances. NOW buying from someone on this board gets more personal and there may be those guarantees you are looking for.
Even an HP unit will have issues. Abuse, lack of needed maintenance. A function quit operating, etc etc. A GOOD sig gen is gonna cost.

Fred

[N6YW]

During my searching, the more you want guarantees and that the instrument is calibrated the higher the cost, even on ePay.
You take your chances. NOW buying from someone on this board gets more personal and there may be those guarantees you are looking for.
Even an HP unit will have issues. Abuse, lack of needed maintenance. A function quit operating, etc etc. A GOOD sig gen is gonna cost.

Fred

No kidding, and you are correct about the cost going up with the guarantee. I found someone locally who is in the test gear business, is a ham and loves boat anchors. He has a late model in mint condition that he said may let go off for around 600 bucks. It's been calibrated too. May have to check this one out.

[Opcom]

I have the older version with the crank knob and I like it. If you can get a clean one do it.

[flintstone mop]

$600 not bad at all with TLC and calibration

[gerry_w1id]

I have owned one for about 5 years which I bought it on ebay for around $550. I wanted frequency and amplitude accuracy to not only perform alignment on various things but also to have the ability to collect accurate data should the need arise. I got everything I expected. One thing I miss is the ability to vary the frequency as easily as I could with my old HP-606B. For example if trying to align a receiver that is completely out of whack, it is difficult to determine just exactly where the receiver is tuned to. For example if I'm looking for  signal at let's say 7mHz but the receiver is really tuned to 6.8mHz I could vary the frequency of the 606B up or down until I heard a signal on the receiver and then make an adjustment. The 8656B is not continuously variable and so you have to set the frequency increment to a low value and press the up or down button until you hear something. That can take a while depending on the increment selected. On the plus side, besides the frequency and amplitude accuracy is the ability to turn the RF output off and on with the push of a button. This is great for checking AGC response when either troublehooting, modifying, or home brewing. Another thing I like is the precise AM and FM modulation settings. I am very happy with mine and I could not imagine doing without it. A couple more things I'd like to add is it came with a temperature compensated reference oscillator and IEEE-488 interface. There is also an input for an external 10mHz reference.

[W4AMV]

A couple more things I'd like to add is it came with a temperature compensated reference oscillator and IEEE-488 interface. There is also an input for an external 10mHz reference.

The 8656 units I have are locked to a common TCVCXO operating at 100 MHz and I divide its output to 10 MHz. Then a common reference is distributed to all 3 units and this is a plus when doing IMD measurements. On your comments for the 606, I agree, however you can store into memory your desired "poking" frequencies and then just press memory recall! Quite FAST.

Alan

[John K5PRO]

The 8656 is old enough (even B) that it can suffer from the HP click button disease. I have used one that had a number of the buttons that didn't respond. I removed the front PCB and washed it in my dishwasher, this made it last an extra few years before it was finally worthless and scrapped. What happens is the little metallic strip gets weakened, its sort of cupped so that when you press it, it closes a contact with a click. Many HP machines of that era used these. Make sure that the one you get has been tested, every button pressed for response. The clickers are no longer available parts.

The HP8657 was the replacement instrument, superior in most ways. They go for a lot more on ePay. I'm using one right now for oscillator for testing big amplifiers at work.