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AQZ HF rig demos

The links on this tab show various demonstrations carried out on various modules that have been constructed as part of a home brew HF rig. This rig was constructed using legacy parts from my stock of bits accumulated over the years. Some of these items are still quite good, and if not used in some way, would most likely end up in landfill. The design is a traditional analogue type, and consists of basic building blocks. The building block method makes it easier to experiment with various sections of the transceiver without having to start all over again, unlike designs using one large circuit board. 

Extensive shielding has been used in order to reduce the problem of cross talk and RF pickup from the various circuits. After having built several HF transceivers over the years, I have found that without shielding various circuits, the cross talk and interference between sections can be quite bad – particularly from the high power RF and PA stages.

I decided the appearance and construction of the case would reflect the look of vintage radios rather than the more modern black box style. This is in keeping with the analogue theme. One can purchase lots of black boxes quite cheaply these days, with lots of buttons and menus. The case used was originally an ACITRON SSB400 radio designed in Australia back in the 70’s. It was not being used and had sufficient room to house this design. As it turns out, every cubic cm has been used.

The rig receiver covers 100kHz to 54MHz continuously.

The front end uses double tuned, top coupled circuits, which cover the whole range using 8 bands, and tuned from the front panel using varicaps. In order to meet modern day frequency stability and accuracy, the VFO system uses microprocessor controlled phase locked loop circuits. There are 2 independent VFOs that can be locked together or tuned independently. The idea is to use the independent VFO to drive a separate receiver system incorporating a spectrum and waterfall  display. The RF tuned circuits are switched electronically so as to follow the VFO selected. The mode selection I have used, is manual. Menu driven mode selection can be used since the manual switching is actually all electronic. I prefer manual selection as I find menu driven selection of important functions not as user friendly.  The idea of this rig is that it be easy to operate without having to fiddle with a series of button pushes.

The rig does have 10 memorises for each VFO but these are used for quick selection of the ham bands. The transmitter section uses fixed tuned filtering for each amateur band with ALC and SWR protection.

The transmitter contains a broadband 10W RF FET PA driver which works up to 54MHz. The 100W PA currently uses bipolar transistors and is limited to 30MHz. In future, it is hoped to replace that with a 100W FET PA.  However at present, suitable robust FETS are quite expensive. My junk box has quite a few of unused, good quality, genuine RF transistors so they have been used for now. The rest of the TX chain uses modern IC speech processing with automatic level control, and also offering compression if needed.  At present, the main area of improvement needed is in the RX front end mixer. It uses an LM1496. But I believe it needs to be a more robust mixer, such as a H mixer, or similar. The rest of the front end uses high IP devices like the 2N5109 etc., and relay only switching (to avoid cross mod which can occur with diode switches).  If the design proves stable, I am hoping to submit it for magazine publication as a source of ideas for other constructors.  

So that is a brief description of the rig, and a lead in to the video demos I have so far made of some sections.


VK3AQZ, Lou.

 

 


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