The N3ZI General Coverage Receiver

I like to play with simple RX’s now and again, it is interesting to see what can be done. I now have several Softrock SDR’r and they really are impressive, both on sensitivity and cleanliness.
The N3ZI is a simple Superhet design with 2 SA612 Mixers, and no RF Amplifier stage. I have the dual band version which has a relay to switch the input filters. What would have been nice is for the relay to be activated by a LOW input then just a switch on the board pads provided would do the job. As it is I had to provide a +ve voltage on a small interface board to switch the relay. As a QRP minimalist, having a relay in a simple RX which gets quite warm bugs me. My complete QRPp TX’s don’t waste that much power as heat.

n3zi-rx-si570-1

I fitted connectors to my board with no modification to the provided pads.

n3zi-rx-board

I decided to use an si570 with USB control for the VFO, interfacing for this is on the same small board. This gives me wonderful rapid QSY with Keyboard frequency entry and Mouse Wheel tuning down to 1Hz steps.
I had problems with the local pop station at first, the mast is in sight and even on some Ham Transceivers the RF noise is modulated with der duh der duh der duh der der from the nauseous music. Being a broad band RX with no input tuning other than the 2 BPF’s there is a great reliance on an ATU, preferably calibrated for each frequency band of interest, it is so easy to tune the ATU to the wrong noise peak and get bad results.

The Xtal filter gives a nice pass band, strong signals produce a lot of images and there is no AGC, which can scare the cat when you hit a strong signal, but it IS a simple RX. After getting used to the VFO injection frequencies involved I have had results on all bands from 136kHz to 29MHz, I have found no QRSS on 30m yet but the 9.996 MHz RWM Frequency Standard signal came in well, which is very handy for finding the second conversion oscillator frequency exactly.

n3zi-rx-9996

30m was the most elusive band to find signals on at first but when I got things right and there was reasonable propagation I saw WSPR which unfortunately is inverted without moving the BFO Oscillator frequency, and PSK 31. This picture also shows the si570 interface and the Xtal filter response in the waterfall.

n3zi-rx-si570-30m-psk

I am determined to see some QRSS on 30m with the RX so I will keep trying. I must admit that personally I prefer the Softrock SDR’s, they make a better simple receiver but this radio is fun.

I thought I would push my luck and tried the RX on 50MHz, I copied the GB3BAA Beacon in IO91ps 57km, 35Miles away using both a Vertical Co-linear antenna and my 5ele Horizontal Beam. The screen shot below is using the Beam.

n3zi-rx-50mhz-gb3baa-io91ps

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More Softrock’ing this time with si570 Sythesizer

A Skype call from out of the blue brought a Softrock A1 Lite+USB Xtall v9.0 in the post. I missed out on this model, I stopped following the development after building my Softrock TX/RX v6.1.

When Alun the owner mentioned USB Lite I thought only of the original Softrock Lite which got its power from the USB port and put its audio into the USB too. I knew of the si570 developments of add on si570 Synthesizers, I have a board which could be used on my v6.1, but not of an integrated Lite kit. Therefore a couple of Skype calls were a bit at cross purposes until it dawned on me that as the computer was asking for USB drivers there must be an si570 involved. Alun downloaded the drivers and got only some very patchy results. Having owned the SDR for a time, it was a supplied fully built unit, and struggled before without success it came my way.

On arrival in the post it rattled rather, that was just some board fixing hardware that had come adrift but it did mean I needed to open the box and re-fit the bolt. As I lifted the board the antenna lead snapped off, an odd one that, the small diameter coax is secured Softrock style by a 2 turn loop of copper wire. The PVC outer, braid, centre core and its polythene insulation all snapped clean after the loop. I can only suspect that the loop was too tight and too much heat was used when soldering thus circumcising the coax. Now that could be a good cause of intermittent signals.
First job then was to re-make the connection.

Next I connected up the board and set up the si570, it should store its last setting but it was showing its internal oscillator frequency. I set it to 28.2 MHz, for a 40m centre frequency of 7.05MHz x 4. Then I started Rocky, it worked nicely, CW and SSB signals were copied and BPSK31 was decoded FB. This is a nice RX and would be easier to modify to 500kHz, hmm, pity it has to go back to its home.

This blog entry will now take the form of a simple quick start guide to using the A1 Lite+USB Xtall v9.0 with Rocky 3.6.

First download and install Rocky 3.6 from HERE.

Next download and install the DG8SAQ Synthesizer Driver and Firmware from HERE.

Also download and install the USB Stand Alone Synth from HERE.
You can operate the Softrock without this but it is such a useful addition I wouldn’t want to be without it.

TIP If at any time the Softrock does not perform as expected remove the USB plug and re insert it, like all things the si570 synth can have a glitch.

On your desktop you will now have these short cuts.

Plug in the Softrock, 9 to 12 Volts Power, to avoid hum loops it is always best to run SDR’s on a battery supply. Stereo Jack to Line in on the Computer, USB and Antenna. On first use Windows will find a new USB device, allow Windows to automatically install the driver.

On all subsequent uses of the Softrock there will be no setting up do do at all and no messages from Windows.

Double click on the USB_Synth Icon the GUI will open. If all is well the Synthesizer online will show Green and the last frequency entered will be displayed, in this case 28.2MHz.

Close USB_Synth and double click on the Rocky Icon, select FileStart Radio, then – ViewSettings.

Right Click and select View image to see the complete picture.

Set your Sound Card in use as I/Q Input Device and Audio Output Device, mine are different sound cards for convenience, they can be the same card for in and out. Leave the Sampling Rate at 48kHz for most standard sound cards, there is no frequency coverage advantage with the si570 by using a 96khz card. Channels Left/Right Q/I is normally correct unless you find the band to be reversed.

Click on ViewSettingsDSP, select Use Si570-USB – set Address to 55, Divider to 4. The Local oscillator box shows the centre frequency of the Rocky tuning Scale. Rocky automatically adjusts the scale to show the correct frequency.
To move the frequency coverage around the band alter the 7050000Hz to 7060000Hz…7180000Hz etc. Do not forget to hit OK to close the box and enable the new setting.

For use on 80m and other bands plug in the appropriate BPF and set an appropriate centre frequency.

Right Click and select View image to see the complete picture.

I think Rocky is the best SDR software for the Softrocks. A very nice facility is the Automatic I/Q Balance,select ToolsAutomatic I/Q Balance and just leave it alone to just do its job continuously. Another the very useful thing Rocky provides is the direct de-coding of BPSK31 just select Mode BPSK31 and point the cursor at the centre of the signal.

Right Click and select View image to see the complete picture.
Next time you want to use the SoftrockA1 Lite+USB Xtal with Rocky all you need to do is double click on the Rocky Short Cut Icon.

Do not forget the very useful Waterfall View.

Right Click and select View image to see the complete picture.

Just use USB synth as a diagnostic tool or if you wish you can change the Local Oscillator frequency using the frequency setting window. However if the frequency is changed by this means the Rocky scale will be off as it will not follow the frequency variation and the calibration set in Rocky will not apply.

I wanted to provide a simple way of re-setting the calibration without any further need for a reference, I therefore started to play with ToolsSi570 Calibration , going through the process several times. Well you can definitely confuse Rocky this way, the calibration no longer made any difference and control of the Si570 frequency didn’t work, often after an attempted frequency shift the oscillator stopped completely.
I tried re-starting Rocky, the computer, altering and deleting the calibration figure and even deleting the Rocky Config file. Finally the only cure was to un-install Rocky and delete everything left in its folder and re-install. This worked fine, so if ever you get problems this will be the best course. This should be the only time that re-calibration should be necessary so the following screen shot shows for the record the dial Frequency to set on Rocky and the True Frequency to enter into the Si570 Calibration window should it ever be reinstalled. This figure of course applies only to the Si570 in this particular Softrock A1 Lite+USB Xtall v9.0.

Right Click and select View image to see the complete picture.

This has persuaded me to give it a little more intensive testing before returning it to its home to see if I can create more glitches. I want it to perform without problems upon its return.

Softrock Lite II for 500kHz and 136kHz

Your intrepid, no expenses spared blogger wanted to try an SDR on 500kHz. Being a big spender and having some PayPal bonus vouchers to redeem I splashed out and purchased a Softrock Lite II 80m Kit, it cost me £4 that !!

Jim Moritz published the details for converting the old Sotfrock Lite to 500kHz and 1softrock-lf36kHz, there is not a lot of difference so I reckon that it should be OK.

 

The main difference is the lack of divide by 8 so a 2MHz Xtal will be needed for 500kHz, as for 136kHz we must experiment.

First step for me was to build and test on 80m, my other SDR is 40m TX/RX so 80m would be a nice band to keep available. Hmm, I suppose I could spend another £4.

srockii-view

I must say it performs very nicely on 80m although FULL band coverage still needs one more Xtal than the 4 I have.

srockii-btm

Well I spent the other PayPal voucher on a 9m glass fibre pole so I followed my original idea of making the Softrock Lite II 80m easily changeable to 500k and 136k.

First of course we need changeable, plug in Xtals, no problem. The Oscillator/Buffer has a bias change for the lower frequencies, 2 resistors need to be removed and another added. I mounted those on spigots for ease of removal. The other changes in this department are added capacitance, this can be added to the rear of the board.

 

The front end is the other change, we must built an LPF which will be too large for the board so this will be separate, this feeds the input transformer which must replace the 80m component.
To achieve this easily I have provided tabs to mount L1 and T1 for ease of swapping.

srockii-filter

It won’t be a luxury band switch job but at least it’s not butchery. Now I need to find a source of 75 material toroid cores.

srockii-xtal

Sound Card for SDR the Hump in the Middle

There is a screen grab elsewhere showing the ‘Hole in the Middle’ of my Softrock TX/RX display. I used YouTube as a resource for storing my videos to use here, now they are a collection in themselves, hence I have produced a video of the ‘Nothing’.

There are some hideous Humps displayed by some users. Using the Delta 44 Sound Card provided the construction of the RX avoids loops, it is possible to obtain a ‘Hole in the Middle’.

SDR Flex Radio Software

I have never liked the Flex Radio Software, I looked at it long before I had an SDR receiver to put into it. I thought that perhaps given proper I and Q inputs it would perform more to my liking. Not so. Here I will show some of my personal dislikes. The Spectrum display is imprecise. Here I hunt down a CW signal and try to follow the Morse using Spectrum Display ‘real time’ and with Averaging. Using other software it is possible to read Morse Code directly from the pulsing of the incoming signal, and so you should. I find the lack of real time display unnerving. Here I hunt down an SSB signal zapping down the band with the Mouse like I do on Rocky software. I have seen another You Tube video of Flex Radio and it did the same as I find, tune rapidly and the display collapses, the very signal you are heading for has gone, you go past, stop and whoa it appears behind you.