TR7, HW101, Corsair, Cubic Astro fans - gather 'round...

[N8YX]

For a long time I've been kicking around the idea of building and fitting a DDS VFO to the 7-line rigs I own - and went so far as to buy a couple of NJQRP's DDS-60 daughtercards. These use an AD9851, which uses a 40-bit control sequence to set frequency. Thoughts were to control them with Parallax BASIC Stamps. Project gets put on hold for 4+ years due to a variety of reasons...

Fast forward to a couple days ago when I began looking at this a little more closely. There are several commercially available kits and lots more "do it yourself" options to choose from:

http://www.wraase.de/dds/

http://www.pongrance.com/super-dds.html

http://www.n4yg.com/ - This one was the most promising - commercial-wise - but the link is now dead.

http://www.karinya.net/g3txq/corsair_pto/ - And here's our best "homebrew" bet.

http://www.hamradioindia.org/downloads.php?d_op=viewdownload&cid=3

http://www.wd8das.net/DDSVFO/ddsvfo.html


A list of rigs that use VFOs which tune from 5.0 - 5.5MHz:

Heath HW-101
Drake TR7/R7
TenTec Corsair I/II
TenTec Omni (A/B/C/D)
Cubic Astro 102/103
Kenwood 120/130/520/820/530/830
Yaesu FT901/902, 101ZD

The possibilities are interesting.

I hope Joe, 'YG's site comes back soon - his offering was the most comprehensive commercial unit. The 'TXQ project bears serious consideration, however.

A stable VFO is just what many of the older rigs need. I would love to equip one of my 103s with two of them. Its PTOs are pretty stable but a synthesizer would be icing on the cake.

[W1GUH]

Have you considered Cumbria Design X-Lock (http://www.cumbriadesigns.co.uk/x-lock.htm)?

Some notes about it here (http://www.cumbriadesigns.co.uk/x-lock-TR7.htm).

Looks interesting.

[NQ6U]

Tell me about phase noise in these DDS VFOs. Ever since getting the R-4A up and running, I've discovered that there are some advantages to going purely analogue. Not that I'm going to turn in the ricebox any time soon but I have to admit that it sure is a lot more pleasant to peruse the ham bands on the Drake than it is the IC-736.

[W1GUH]

Tell me about phase noise in these DDS VFOs. Ever since getting the R-4A up and running, I've discovered that there are some advantages to going purely analogue. Not that I'm going to turn in the ricebox any time soon but I have to admit that it sure is a lot more pleasant to peruse the ham bands on the Drake than it is the IC-736.

re: Phase noise.

Good thinking about "purely analogue." After years of being conditioned to rice box synth's, I was blown away with the Drakes...both the TR-3 AND TR-7. The difference was breathtaking. That's one of the reasons that X-Lock looks so inviting!

[N8YX]

Have you considered Cumbria Design X-Lock (http://www.cumbriadesigns.co.uk/x-lock.htm)?

Some notes about it here (http://www.cumbriadesigns.co.uk/x-lock-TR7.htm).

Looks interesting.
I've also been acquiring parts to build a huff-puff setup. The Cumbria might be the best way to go in the case of the 7-lines because one has enough space to fit the unit into the parent radio.

Not so the other equipment. Maybe the Corsair has enough case space to accomplish the trick. I may have to buy one and find out.


Tell me about phase noise in these DDS VFOs

The general rule of thumb is: The higher the clock frequency of the reference oscillator and the lower the DDS output frequency, the less phase noise will be generated. AD was supposed to have come out with a device which utilizes a 200MHz reference and its harmonic/noise content will rival or exceed that of the best analog sources which we're discussing.

One of the links above contains a bit about an AD9832-based unit, and a TR7 equipped with this construct turned in better performance - phase noise wise - than when using its OEM PTO. On my shopping list is a good spectrum analyzer - that will be the definitive means of determining purity. Too much "grass" on the display and I won't put the unit into my rigs.

[W1GUH]

Thanks for that great info.

[K7SGJ]

Thanks indeed. I may get one the N3ZI units to resurrect an old radio I built years ago. Have to build a buffer/amp stage most likely, but it twould be fun to nutz around.

[N8YX]

N4YG's site is back.

5055

http://www.n4yg.com/Corsair.html - for you Ten Tec fans

http://www.n4yg.com/Drake.html - the Drake Gang is well represented

http://www.n4yg.com/Heath.html - as is Heath


I'm going to e-mail Joe and let him know about possible applications within the Cubic line - and see about grabbing three of the kits. One for an R7, the other two for an Astro 103.

He specifies a rotary encoder for use with the kits, and I'm not sure of its service life. My preference is the Grayhill 63R256D (~$50) which is spec'd at 300 million revs/failure. It also uses a ball-bearing shaft support arrangement and the rotation is smooooooth. Well worth the cost difference, IMO.

[KA9MOT]

That Drake in the video is sweet. I have always loved the look of Blue back lighting.....

[W3WN]

There was a thread on the G3TXQ board last fall on the Ten-Tec reflector. In general, it got very good to rave remarks.

The gist of the thread, though, was talking about using that board as a DDS replacement for the existing Corsair/Corsair II PTO unit.

Personally, I'd be interested in a design that would use this board, or a similar board, as the core of an external Remote VFO. That would permit all of the advantages, without compromising the rig itself... although at the moment, it's a bit academic, since my Corsair II & RVFO work just fine.

[K7SGJ]

I order the N3ZI board. He had info on changing parameters in the eeprom. Since they all use the same DDS IC, I suppose the others are similar in form and function, but I liked this one. It will be fun to experiment with it. I plan to eventually build an external VFO for some of my older stuff.

Thanks again for the links.

[N8YX]

I order the N3ZI board. He had info on changing parameters in the eeprom.
Tell me more - on the site, or elsewhere?


Thanks again for the links.
No problemo. I heard back from Joe, 'YG and he's interested in the Cubic project. Said I would only need one DDS unit (as it incorporates two separate VFOs) but I like the idea of fitting both and having four. :yes:

[WØTKX]

Oh my yes, 'YG has got it dialed in for the good 'ol Omni D as well... :agree:

[K7SGJ]

Tell me more - on the site, or elsewhere?


No problemo. I heard back from Joe, 'YG and he's interested in the Cubic project. Said I would only need one DDS unit (as it incorporates two separate VFOs) but I like the idea of fitting both and having four. :yes:

Yes, it's on the website. All the DDS circuits I've explored all use the same basic AD9834 design, which has the dual VFO capability. Where they differ is in the use of eeproms or PICs etc. I am also ordering a Bournes optical encoder from Jameco. It's about $22 and in stock. Others can get it, but it would be a factory BO. I think the optical encoders will perform much better than the mechanical. I'll find out when it all gets here and I can start playing around with it. I'll post anything worth passing on.