'PANADAPTER'

NEW, G4HUP's buffer amp, Jan 2nd, 2014

NEW, Cristi's build also. 22nd Dec 2013

NEW, F1CHM's build photos added. 27th Nov 2013


Nov 2013:- It's been a long time since I updated these pages from the original notes..

In the meantime, I discovered another PANADAPTER type project on the Web, using a DSP system. This looked appealing and I also mentioned it to VK3ATC, who quickly built one up and is very happy with it. I followed on and have now built a "proto" unit too.

This DSP system used an AVR Atmega8-16 to process the signals into a 60KHz wide display on a graphics display. The original design used a 128x48 display which is a bit hard to find, so we both used "HG12605" 128x64 displays, which are very cheaply available here in VK3 and possibly on eBay also. Some types use different polarity chip selects but this can be overcome by altering the source code "ifspec.asm" module.

Here are a couple of pictures of my work so far plus other builders. The original design used an input at 455KHz so for use in most transceivers, a down converter is required. We both used an SA612 mixer to convert and it appears to be OK so far. Crystals for the mixer are easy to find also when using either a 10.695MHz (10.24xtal) or 10.700MHz (10.245xtal) IF system as is used in PICASTAR, which we both have built also.

Overall, we found the gain to be a little low and a single transistor amplifier stage needs to be added after the down converter and BPF.

The original design uses 455KHz input as above but it 'might' be possible to alter this to suit the actual IF frequency of the Transceiver directly, but this has not been investigated further. It would mean high levels of the IF frequency being present on the Panadapter PCB which might interfere with the transceiver unless very well shielded.

PARTS REQUIRED:-

You may have difficulty in finding some of the parts, especially the IC's. In my case, they were purchased from www.mouser.com but be aware their shipping charges are high. $39 to ship to Australia for example. Best to do a group buy with your friends if possible to share the costs. www.utsource.com have some of the parts also, but not the MAXIM devices. The project can, though, be built without them, by bridging input to output.

This is a test only.

The VK3PE 'panadapter.

As you can see above, the Panadapter is quite simple. This H/B PCB mounts on the rear of the LCD display. The down converter is not shown here as it's a separate PCB. The AVR Micro is at the top and the signal comes in at the RH side of the PCB and is conditioned (converted to I&Q signals, filtered then converted to digital signals) and enters the Micro on the left side.


New Dec 22nd 2013:

Hi Glenn,

I`ve attached to this mail two pics with my panadapter (not quite ready yet). Unfortunately I could not find the MAXIM IC`s, so I will use it without these chips. For now I have a self oscillation in the 455KHz osc (about 30MHz HI), and the transistor stage between downconverter and panadapter PCB is not made yet.

But it works, and this makes me happy. Thank you for support and PCB files. In my case, the CSR and CSL are reversed (crossed, probably this is the type of LCD).

That`s my news. For now I want to wish you and your family all the very best, good health and a Merry Christmas! (and why not, happy building as before)


73 and best regards,

Cristi YO3FLR

 


Michel, F1CHM has also been building this version from a home made pcb pattern by vk3pe.

Michel is a prolific builder and had his version up and running in only a few days.

 

 

 

 

 


 

1st December, 2010, See end of page for a working Panadapter !

 

A "Panadapter" is a device which is connected to a receiver's IF, at a point before any roofing filters. It may then be used to display signals near those to which the receiver is tuned. Of course, a suitable display is required. In the older days of Panadapters, long persistence display tubes were used. In these times, the display may be via a PC or for a self contained unit, some type of graphical display.The horizontal axis is frequency (centered on the receiver's current frequency) and the vertical axis is signal strength, normally calibrated in some fashion. A Panadapter is a form of spectrum analyzer.

These days, there are quite a few small graphical displays available on eBay. In particular, the 128 x 64 dot type are very cheap. Under US$10 if you look around. This is the one I bought, a "Lumex S12864 G". This one has in-built LED backlighting, but more importantly, has its own bias supply. Some displays need external 12 or 13V etc. This one only requires a single 5v supply. It is a little port hungry on a Microprocessor interface though, requiring about 12 lines.

I wrote a quick bit of code to try it out. This represents several signals either side of the centre frequency. At the bottom is a scale with centre frequency and +- 10, 20KHz. This is not the final version. Since there are 128 dots across and 64 down, I have allocated a section to the left (dotted line) of 8 dots across for a scale (not there yet) of signal strength with the bottom 8 dots vertically, being the frequency offset.

I may not use the vertical bar idea but use a single dot for each horizontal point, forming the more usual graphical display for a Panadapter. The exact scaling on the bottom is yet to be determined and is limited by the crystal filter used.

WHERE I WILL USE IT:-

I happen to be be building a PICASTAR transceiver. (See Yahoo groups) So I thought of adding a Panadapter display for it. My thoughts are for the IF signal at 10.695Mhz to be buffered out to a point where, say, an old 10.7MHz 25Khz wide filter could be used. (I have since bought a couple of 10.7MHz, 35KHz wide, 8 pole filters on eBay for AUS$16. Perfect.) Mix this down to maybe 6MHz where cheap crystals are available for a filter to get 200Hz resolution. The filtered output signal can be measured by an AD8307 log detector (or use an FM IF chip with RSSI {signal strength} like the NE604, which is cheaper and easier to get) The local oscillator for the mix down to 6MHz could be done with a DDS controlled by a micro, which sweeps the DDS across the bandwidth of the crystal filter. The micro would convert the level from the log detector using its in-built analogue to digital convertor and then display it on the graphics display.

Here is the bottom of my PICASTAR. Not too tidy just yet as it will be moved into a new homemade box, similar but a little larger than this home made one. The mixer (known as Magic Roundabout) is located at the bottom. The Panadapter will interface to it with a buffer board. Centre is the IF board and above, the T/R timer board.

All of this was prompted by a recent Panadapter article in QEX (I think March/April 2007) and I am about to try an adaptation of this article, using parts to hand, specifically the 128x64 dot graphical display, driven with a Motorola MC68HC908GP32 or QB8 micro. The Panadapter will be self contained, with a (buffered) connection from the PICASTAR IF board, before the 10.695MHz (6KHz wide) roofing filter.

The first thing required is a buffer stage to tap off the IF signal. This should not load the IF stages and it should also provide a low impedance output, for the following stages in the Panadapter. I was looking around the WWW and saw an article on using FET's as source followers. Ref "FET Principles and Circuits, Nuts & Volts Magazine (June 2000), Figure 8." I breadboarded up this circuit for testing: It's not a single FET. It also has a bipolar transistor in the biasing and output stages. It seemed OK, so I etched a PCB for it.

I used BC547's in prototype, but 2N3904's in PCB version.

If this buffer proves OK with low signal levels, I will fit it to my PICASTAR, with a co-ax cable and connector on the rear. A shield will be fitted around the PCB. At this stage, the Panadapter will probably be external, but if I re-build my PICASTAR in a new case, I may incorporate it also.

Here is the information for the PCB in pdf format. It's given as is. I have not done any further testing at this stage.

Following the buffer, some amplification may be needed, followed by a mixer, to mix down to the 6MHz filters.. I will use a SBL type mixer initially as its quick and easy. Later I may go to an H mode mixer, as is used in PICASTAR.


Another Buffer Amplifier

NEW Jan 2nd, 2014:- PANORAMIC ADAPTER TAP (PAT). Recently found is this buffer amp by G4HUP, which is also available in kit form.

Refer to G4HUP's web page in link above for schematic and other details. He has a kit available also. This one does have some gain, so maybe more usefull in the DSP Panadapter version. VK3PE has made up his own PCB from G4HUP's schematic. Preliminary testing shows good gain. In fact maybe too much, will see how it performs in the DSP based Panadapter when fitted to my PICASTAR.

I had to fit a leaded J310, until an SMD one becomes available. Its on the left side of the picture. The other two transistors (BFR92) are SMD parts. The output LPF and attenuator stage is not yet fitted. This PCB is about 1.6" * 0.75".

 

More later.........


1st December 2010: This is an analogue based Panadapter. Signals off air are down converted and measured for signal strength as the local oscillator of the device is swept across the range in steps. The older panadapters we are all familiar with, used this scheme, as DSP was unknown then ! Its still very effective though.

A friend (Peter) has taken up the Panadapter project and now has a working prototype. Very impressive result.

A 128x64 graphic display is used with an Atmel controller. Sweep rate seems very fast so updates are quick.

Below are some pictures of actual on-air signals. There is some 'ghosting' due to the fast sweep and slow camera !

The sweep width is 200KHz......

Above: currently only a 1KHz home made filter is fitted. A 200Hz will be added later.

I will add an IF output on my STAR and try Peters Panadapter in the near future. <vk3pe>


 

Page created by VK3PE

 

 

Updated:- January 6, 2014