Has anybody here used the AD9851 DDS signal generator? I've seen them on EBay for what seems to me to be a reasonable price.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270940101864

Right now, my only signal generator is an aged Heathkit, and I have doubts as to its accuracy and stability based on past performance (the analog dial does not help matters any...). One day I may get around to rebuilding it, but meanwhile I am trying to find a low-cost generator strictly for doing alignments, and this one SEEMS to fit that niche.

It's only part of a signal generator. With 1 volt output, you will need to build a calibrated attenuator to take that level down to 1 microvolt in discrete steps (that's 120dB of attenuation !). You will also need to build an adequately shielded cabinet to prevent leakage radiation from the pc boards from corrupting your measurements. That may be a challenge, while providing a window for viewing the digital display. You will need to build a amplitude modulator circuit - if you want the AM modulated output option provided by most signal generators.

So, as impressive as the digital device's specs are, there is still a big project required to make it a useful device.

--Chuck

.... and besides they can't even get the Chinglish translation correct to describe the product. Can you imaging trying to understand the data sheet it comes with - if it comes with one!
Ebay has Leader and Wavetek function generators auctioned used for around that amount. Don't be too eager to give your money to the land of rice and honey.

The days of the $3.00 "all on one chip" or PC based ligitimate RF signal generator are still a long ways off. Even if you went through the process to fabricate what would be needed to initially make that board operate, it wouldn't end up being much better than your Heathkit performance wise. There is no shielding for the signal path at all, which would be the biggest problem. Forget about calibrated attenuation, as they state the signal ampltude gradually fades over 1 MHz and I don't see any way to work around that which will never take it anywhere beyond turd status. Then as mentioned you'll need a source for modulation. I wish RF signal generators were as easy as plugging the wall-wart in to that thing, but it's not the case.

-Mark-

I would like to differ with "Mars" on the suitability of function generators for radio alignment. Function generators generally have an output level in the low volts, needing a calibrated attenuator for alignment use. They lack amplitude modulation capability. They also tend to lack the shielding necessary to prevent sneak path radiation to interfere with alignment measurement. They are a great toy to have on your workbench, but unsuitable for any kind of precision work.

I use a Tektronix function generator for casual audio work, a General Radio 1001A for alignments and an EICO signal generator for times when the GR generator is just too heavy.

--Chuck

The board might be adequate as a function generator having the sine and square wave outputs being used for situations where shielding isn't a big concern. But that said, and what Mars said, one can get a decent used function generator for the same price. As an RF generator to use for radio alignment, the board in itself is far from adequate as are just about all function generators.

-Mark-

Got to agree with the crowd, nixing the function generator, too much down side, with leakage, drift, and lousy attenuators. A lot of the kit and service type "RF" generators have the same problems.

BUMMER! I wish I could at least find a cheap frequency counter that worked properly so I could calibrate my Heathkit. I made the mistake of buying one on EBay, and it turns out it only works well with hand-held radios. I can't get it to pick up a signal from my Heathkit, even if I wrap a loop of wire connected between my test lead clips around the frequency counter's antenna!

Have you tried feeding the signal generator's output directly into the frequency counter?

Dave

How would I go about doing that? The antenna is a "rubber ducky" that screws in to the top of the counter's case (it's a hand-held).

This is the frequency counter I have, by the way:
http://www.ebay.com/itm/FC-1-Frequency-Counter-10Hz-2-6GHz-for-2-way-radio-FC1-/110591117700?pt=LH_DefaultDomain_0&hash=item19bfbe8984

According to the specs, the antenna (useful only for UHF) uses an SMA coaxial connector. So you will need to make a cable that ends in the same type of connector that the antenna has. Do the instructions tell how to use the counter for the lower range of frequencies?

Dave

Same way as for the upper range; just push the buttons until you're on the right setting.

I found a short version of the manual on line and, you're right, they say nothing about replacing the UHF antenna with something else if you want to measure lower frequencies. But they say not to apply more than xx volts to the input so they must assume you'll be using a cable for some measurements. (I forgot what the stated voltage was.) I think you'll be happy to see that, when you connect the counter to your RF generator with a cable, it will read its frequency.

Dave

I'd suggest you get a bench type counter, HP, Fluke, or Tektronix. In order to easily use any of the counters, You'll probably have to bring out a separate connector ahead of the attenuator.

One word: money. Or more precisely, a lack thereof. I have never found one on EBay that I could afford, once the bidding got going.

Fifty bucks, minus the plug-in, at a local ham fest. You can find counters on ebay easily for the same price or less, just don't bid till literally, the last ten seconds. Bid early, bids it up = no bargain. A lot of guys here have gotten bench counters for less than that.

I never suggested using a function generator for RF alignment -- I know better than that! I was simply replying to the OP's link to the brand/model and noted that the foreign dealer couldn't get the translation correct, therefore the likelyhood of a poorly written user's manual.

You have to keep at it and at it and not give up. Eventually some day lady luck will be with you. Too often those high auction prices are jacked up by the sausage stuffed, fat bellies with equally fat wallets! They make me sick... right along with sausage sandwiches!

You just have to keep at it with E-Bay. I got my nice 5334A universal counter there last year for $35.00, without a single competing bid. 500 MHz+ counters tend to command big bucks, but for the regular Joe just working on radio equipment that doesn't involve VHF or UHF cheap good working 80-100 MHz counters, even excellent quality ones, are abundant.

-Mark-