My Dream DF Display

[pauldbnut]

Wondering if such a display is feasible, given a decent antenna array and multi-channel receiver...
Obviously need to tune a specific channel (e.g. a VHF BC frequency).

Please excuse horrible graphic

[Simon G4ELI]

Yes it is if you have a quad or better still 12 channel coherent SDR.

[jdow]

Technically possible. Maybe even technically feasible. But, technically meaningful to any huge degree - not so much unless you accept pretty large error bands on the antenna pattern. Modeled patterns are merely theoretical. Local environment imposes a humongous accuracy tax.

{^_^}

[pauldbnut]

Hmm, thanks for the reactions.
Was guessing 3 or 4 was the minimum theoretical, 12-channel would be brilliant but crazy expensive.

At the low end angular resolution would be fairly crap, obviously, better with more channels.
Also at VHF would expect a lot of distortion from local terrain and other large structures - but this would in itself be informative (reminds me of the old BBC FM multipath surveys).
Had hoped there might be some value for DX - spotting possible catches otherwise masked by stronger stations, steering main beam to help attenuate the big guy.

Then there's the interesting extension of nulling selected directions, with visual feedback how well it's working.
That's about all I do these days, dream .

[Simon G4ELI]

Technically possible. Maybe even technically feasible. But, technically meaningful to any huge degree - not so much unless you accept pretty large error bands on the antenna pattern. Modeled patterns are merely theoretical. Local environment imposes a humongous accuracy tax.

{^_^}

I've seen a 12 channel VHF unit with a 0.5 degree accuracy.

[jdow]

Free space I presume. Multipath can screw you up no end, especially short differential difference multipath. I've seen that produce over 5 degrees of apparent phase change from nominal at 1575.42. The multipath came from reflections from poorly designed type-N to RG223U bulkhead connectors that had a modest reflection coefficient when testing the BITE system for GPS satellite the pre-launch test receiver using a "trombone" transmission line. I quickly became very wary of the effects you get with multipath.

This was confirmed years later when I sat and watched multipath walk an Inmarsat-M tracking antenna off boresight with a grazing incidence signal from the then Atlantic West satellite received in Torrance California. (Pacific was just as bad. Both were under 15 degrees and suffered vicious multipath.)

{o.o}

[Simon G4ELI]

Yes, VHF free space. HF is very, very difficult.

[pauldbnut]

Not at all the same display, but the following caught my imagination some time back:

https://www.qsl.net/dl4yhf/speclab/colourdf.htm