G4HUP Direct Frequency Synthesiser Documentation - Issue 2 PCBs

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DFS Issue 3 Documentation    

Note: the current batch of Issue 3 PCB's will be the last for this product.

Technical Update - Aug 2011 Some experimentation has taken place with the operating voltages of the DFS. When run off the 'standard' shack voltage of 13.8V, the dissipation of the regulators (esp the 8v reg) is quite high, and DFS units tend to run very warm. I've been playing with lower operating voltages, and have found that they will run with no deterioration in output level or quality down to +10v. Below this voltage there is insufficient headroom for the 8v regulator circuit.

When run at this lower voltage, the dissipation of the DFS is very much reduced and consequently it runs much cooler. Therefore, I recommend that if possible you should provide a dedicated DC supply of approx 10 to 11v for the DFS - especially if it is enclosed in another case!

Changes and Updates in Issue 3

There are several improvements and changes in the Issue 3 PCB which are intended to improve the performance and versatility of the G4HUP DFS PCB. Changes to the circuitry are minor, but in some cases significant - check through the items below:

Onboard Diplexer

The diplexer that was recommended as a modification to Iss2 PCB's is now provided on the PCB. For any case where the HF input to the final mixer, M601 is approx 15% of the VHF freqnecy or greater, the diplexer is recommended.

Replaced MMIC devices

The MAV-11 in the VHF multiplier has been replaced by a Siemens BGA616 device - saving real estate and giving greater gain flexibility, since an attenuator has now been introduced between the two amplifier stages. The final MAR6 MMIC has also been swapped for a BGA616, giving greater potential for increased output level if required.

What's gone?

Well, to make way for the changes, I took out the 'daisy chain' capability of the input buffer stage - I'm not aware of anyone ever implementing that, so don't see it as a great loss! Also there has been some small movement of some of the components on the PCB, especially mixer M601 - this was quite difficult to solder in place previously, and now there is a bit more celarance to the side of the box. The input and output sockets have moved a bit further towards the centre of the box too.

Other Comments

The majority of the Issue 2 doumentation is still relevant - worksheets, frequency schemas, attenuator tables, filters etc. A new manual is available for Issue 3 PCB - this has been updated to use a more relevant example for European operators, based on a 106.5MHz DFS version.

General Documentation:

Pi Attenuator resistor values

DFS Issue 2 Filter page - Information on all proven frequency schema and approriate filters

DFS Logic Divider Config Guide for selecting ratios and setting links correctly

DFS Issue 2 Design Worksheet for developing new DFS implementations

DFS Issue 2 Frequency Calculation worksheet an aid for proving multiplier/divider and mixing products. This example is pre-loaded with the data for the 101.75MHz DFS version, but everything can be overwritten

DFS Issue 3 Technical Manual, including circuit schematics and parts placement diagrams

Click here for Errata and updated information

Notes on different Frequency Schema versions


Page created 18 May 2008

Page last updated 7 Apr 2012