SoftRock 6.2?

[M0GLO]

Anyone here used the SoftRock 6.2 rxtx?

I just ordered it and was thinking of modifying it for use with a DDS instead of crystal controlling it.

Quick question. Why DDS and not PLL? Isn't PLL easier and if you have 5 kHz steps, you can step right enough to stay within your receive and transmit passband.

I think Ryan is really into this softrock stuff.

[N2RJ]

Yup.

I've built the whole line of Softrocks including the rxtx.

DDS is definitely possible. There's info in the yahoo! group using the AMQRP's DDS-60 kit. I have a DDS 60 and have used it with the receive only softrock but have not tried it with my rxtx.

However, the most creative use for a Softrock I've seen is where it's fed the IF from a conventional transceiver. There's even a build of HRD that integrates the softrock seamlessly with PowerSDR.

[N2RJ]

Quick question. Why DDS and not PLL? Isn't PLL easier and if you have 5 kHz steps, you can step right enough to stay within your receive and transmit passband.

I think Ryan is really into this softrock stuff.

PLL is easier if you were using discrete components, but thanks to DDS chips made by Analog Devices (AD9851) and others, DDS is easy to implement. And of course, DDS is better, so it's a no brainer. :)

[M0GLO]

That's what I was thinking as well, and with the DDS-60 kit being available for like 20 bucks it makes it an easy choice.

How do you like the 6.2 kit? I picked up the 40/30 kit for my trip to the UK.

I've also picked up a couple of BLF177's for an amp to use for it. Should get about 180 watts out with a watt in.
I'm basing the amp design on this:
http://www.nxp.com/acrobat_download/applicationnotes/NCO8703.pdf
The circuit they give looks OK, but I'll have to add some band pass filters to clean up the harmonics.

For the trip I don't really have time to get the DDS setup together, but I did want to move the whole thing up a little in the band so I was thinking of bypassing the 30M crystal oscillator and using a SG51 @ 28.6363MHz to move the center frequency up to 7.1590. That should give me RTTY/SSB and the top portion of the CW band, and using the low crystal oscillator so I can still use the DX/PSK portion of the CW band as well.

Have you noticed any problems with moving the bands around on these?

I was messing with the schematics this evening to see how I could hook it in.

[N2RJ]

Moving the bands around is no problems at all, but it gets a bit less sensitive around the edges In fact, with a 192kHz sound card I pick up the broadcast stations on the lower end of 40m.

Looks like to me the DDS chip is still 10 times the price of the PLL, but you are right in that the phase noise is typically lower on a well designed DDS rather than the well designed PLL. But essentially, your phase noise is dependent on your design anyway. With DDS, you will need a clean reference, and with a PLL, you will need a clean reference and a clean VCO.

There are ceramic resonators with a high Q although not as high as a crystal. This will allow for tuning over the whole band possible.

I am a member of the DDS Yahoo group. They have quite a following, and like politics, there are people who refuse to buy reality when it comes to measuring phase noise.

[N2RJ]

Looks like to me the DDS chip is still 10 times the price of the PLL,

True, but irrelevant when you're using free samples from Analog Devices.

[M0GLO]

And like I said, the cost of a DDS-60 is around 20 bones.
I spend more than that on toilet paper every month.

[ad4mg]

And like I said, the cost of a DDS-60 is around 20 bones.
I spend more than that on toilet paper every month. :shock:

Sounds like an issue with your diet ... :lol:

Quick question. Why DDS and not PLL? Isn't PLL easier and if you have 5 kHz steps, you can step right enough to stay within your receive and transmit passband.

I think Ryan is really into this softrock stuff.

PLL is easier if you were using discrete components, but thanks to DDS chips made by Analog Devices (AD9851) and others, DDS is easy to implement. And of course, DDS is better, so it's a no brainer. :)

Yeah, well when actually working with these projects and running simulations knowing what you can use for circuits, there are ways of improving on the new DDS with old PLL technology.

Looking at the spec for phase noise on the AD9851 reads a level of -132 dBc/Hz @ 1kHz offset. With a properly designed VCO using a ceramic resonator, a PLL can be in the area of -155 dBc/Hz @ 1kHz offset.

Couple this with a vast drop in spurious emissions from the DDS design specifications, and a brainer says to use a PLL. But it is a lot more work for a 23 dB improvement.

[M0GLO]

Hey Ryan where did you hook the DDS-60 into, right at the clk pin?

[N2RJ]

http://groups.yahoo.com/group/softrock40/message/5310

[M0GLO]

Awesome, I've been searching for that for a couple of days.

Thanks!

After comparing the schematics between the V6 receiver only information and the V6.2 RX/TX the correct location is C45 right after the emitter of Q13.
The V6 notes you pointed at give the cap as C7.

It looks like the correct way to do this would be to depopulate the xtal oscillator section, replace R57 with a 1/4w 50 ohm and solder the RG-179 at the emitter solder point where Q13 used to be. That way I get the 50 ohm termination using the existing mount point and have a clean connection for the DDS input.
Once I've tested and tuned this up with the crystal I'm going to depopulate the oscillator section and give the DDS-60 a go.

[N2RJ]

Yep, pretty much.

I didn't depopulate the osc section though. I had bought several of the softrock kits and I just didn't assemble the osc section to begin with in mine that's connected to the DDS60.