sposullivan

This is the Faraday spectrum of the calibrator that I mentioned above: 

Ah yes maybe so, the DI calibration step done by the ddf-pipeline, not the prefactor one you mean?

Annoyingly this effects all four surrounding pointings (P219+52, P223+52, P219+50, P223+50). This problem is also noticeable for the P17 field due to an 84 mJy polarised source (the above source,...

No, there is a small variation within each field and a larger variation between fields for %p. The RM spread is unrealistically narrow. 

Potentially yes if any additional real peaks are sufficiently distinct in RM space eg. the smallest peak in these FDFs are close to the Van Eck values (the ones at...

A potential way to identify the fields with fake sources (and just bad fields) is by looking at the median absolute deviation of the RM and the degree of polarisation...

@twshimwell In terms of a field with a decent ionosphere but very few polarised sources, what about P178+67? No polarised source above 1 mJy/beam in this field.

Below are the details of how I insert a fake polarised source into the prefactor visibilities and then image with the ddf-pipeline. It crashes pretty early in the pipeline for...