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G4HUP DFS takes 2nd place in SVHFS Design Contest!

The Flexible DFS PCB concept, and its support resources here on the web-site, took second place in the Design Contest run as part of the Southeastern VHF Society Conference in Orlando, Florida, 25-26 April, 2008. The Conference Paper was based on the 124.5MHZ DFS for 24GHz operation, and a separate presentation demonstrating the versatility of the design was made to the competition judges.

My thanks to Sam, G4DDK, for presenting on my behalf, and congratulations to N5AC, the overall winner.

Issue 2 DFS PCB!!

A revised PCB for the DFS is currently on delivery from the fabrication house. This PCB provides a little more flexibility in terms of the divider configuration, and incorporates better support for screening of circuit stages to reduce spurii levels - lessons learned from the 92.25MHz and 124.5MHz versions - thanks also to input from Brian, GM8BJF.

Other changes include:
  • moving to Toko 7k coils instead of 10k - because they are still current (10k production ceased some time ago, and stocks are becoming harder to find), and it avoids any coil re-winding, since full ranges of inductance are stocked in the UK.
  • better filtering available (two stage LC) in both low frequency signal paths
  • re-arranged and improved filtering after the first mixer - now there is a 2 stage BPF immediately after the mixer, and another one following the amplifier/multiplier
  • change to Minicircuits ADE series mixers - they are cheaper than the A-06 package (SBL-1, SRA-1) types and consume less PCB real-estate
  • change to D-PAK regulators, mounted on the top side of the PCB - this allows the PCB to be mounted just a mm or so higher in the box, and avoids the SMA sockets fouling the lips of the box covers
The Iss2 PCB will be available for delivery around the middle of May. To support it I will be extending my component stocks to include the ADE-1 and ADE-6 mixers, and the necessary range of Toko 7KLL inductors. I will also order crystals at your request but I will not be holding stock of them.


Current Developments

Two other items are undergoing development at the moment - these may or may not make it to 'products' depending on interest! They are:
  • a 1 in 4 out distribution amplfier, suitable for both 10MHz or 1575MHz GPS antenna feeding within the shack. It will support any other frequency within the range of the MAV-11 devices that it uses, and incorporates the option for GPS antenna power feeding (5V at up to 80mA). There is an optional output for feeding another splitter
  • an outboard amplifier/multiplier for the DFS. To replace the LO xtal in modern DEMI transverters, a source at around 190MHz is needed - 2 times the normal DFS frequency. Also it can sometimes be useful to replace an LO xtal with a more easily synthesised DFS frequency - for example, the DB6NT 9cm LO starts at 135.667MHz - but 101.75MHz is a better solution for a DFS. Experience has shown that the DFS output is too clean, and that having 4 times the DFS frequency (407MHz) is a good solution as it is the same as 3 times 135.667MHz. This unit has options for filters using Toko 7HW 2 chamber helicals, or S18's (good up to 250MHz)
E-mail me from the home page to check on the current progress of either of these items.


DFS Frequency Calculation Worksheet

An Excel based worksheet which allows you to experiment with the numbers for a 'standard' DFS architecture -ie the configurations for which the G4HUP DFS PCB is intended. Using this sheet you can confirm the divider ratios, multiplier factors, mixer products and filter requirements.

DFS Design Worksheet

A single page worksheet has been made available as an aid for designing DFS implementations. You can download and print the sheet. All the potential features of the circuit are indicated, and you can use the sheet to identify which functions you need for your design, and which filters you will have to implement

Page Created 26.11.07

Page Last Updated 27.04.08