[hpsdr] Cyclops Update

[Phil Harman]

All,

Here is the latest status of the Cyclops project. With the assistance of Warren, NR0V, and Bill, KD5TFD, I’ve been investigating an alternative architecture for Cyclops. This is explained in detail on the Wiki but basically we use an architecture that will not eliminate images and then use software to assist with their removal.

Initial tests have been very successful and Warren has developed an innovative set of algorithms that effectively perform the image removal.

This is not a panacea for all image conditions e.g. very wide band, complex and fast changing images will present a challenge. However, there will be software options to turn the image cancellation off and such conditions are hopefully infrequent. 

The solution is looking like a single Atlas bus board that will include a 0 – 4.4GHz Spectrum Analyser plus tracking generator. It’s planned that this can also be used as a VNA. The supporting boards will be a standard Mercury board and Metis. Given how full the FPGA on Ozy is now, and the fact we have 500kB of RAM on Metis, then its unlikely Ozy will be used. 

I’ve not done recent work at GHz frequencies so would appreciate input from our membership who have microwave design and construction experience. 

Some items that require design input are:

1. The previous Cyclops design used a Mini Circuits SYM-25DMHW first mixer. Since this is only rated to 2.5GHz we need an alternative. What is recommended – active or passive? The Analog Devices ADL5801 looks like a possible candidate.

2. My current prototype has a noise floor in the –140dBm region – is this good enough or should we add a wide band pre-amp – if so what part? If we use an active mixer do we in fact need a preamp?

3. Should we use an on-board switchable attenuator or external ones (e.g. Mini Circuits) that can be directly connected to an SMA socket?

4. Given the wide frequency range input filtering will be desirable, so that we don’t suffer from signals mixing with harmonics of the LO. Again there are external SMA based filters available (e.g. Mini Circuits) or should we include these on board – if the latter how do we implement and switch them?

5. Is FR4 PCB material going to be acceptable over this frequency range given that we immediately down convert to a low IF and MMIC ICs are an easy way of making up any losses in the Tracking Generator output.

Comments, suggestion and ideas are requested!

73 Phil...VK6APH 
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