Gonzgo, another option is the Garmin MSC 10 which is worth while step up from a LT500 - a bit cheaper than the SCX20

Always very cautious of spec claims made from these low cost “gps compasses”, especially with such small antenna baselines. I suspect they are not delivering true gps compass solutions, but more a slightly enhanced magnetic compass solution, or potentially just aiding with the internal deviation offsets. They may even revert to DR/cog when signal quality is very poor and/or applying significant damping to mask errors. And you’ll never know which solution is being applied. I recall a top brand starting with g advertising a 10hz GPS with USB in recent years, but on investigation it was updating at no better than 0.5 hz and simply serving a DR pos at 10hz…

GPS compass solutions such as from SBG and hemisphere (c. £10k installed), with dual antenna setups with over 0.8m separation have been extensively tested in our environment by many teams and have fallen short in reliability (performance wise).

Here you might not see many on high end racing boats, where the choice really is to go full FOG, or build your own HDG offset table in your instruments.

rvsail wrote:

I have been tempted to build my own using a Control board and two antennas, placing the antenna's at the back corners of the boat (around 4m apart).

https://www.ardusimple.com/product/simplertk3b-heading/
 

That would be quite some project!

After 2 years working with a military/helicopter/drone grade system with direct intervention from their engineers, I'm dubious of the 'real' output of these low cost units, especially with such a small baseline.

A relatively stable environment of a 12m might well be OK - possibly better than a poorly calibrated LT500/1000/P9 etc....but not by much. I'd rather know what my repeatable errors are, than have a device mask them.

gonzgo wrote:

Since FOG systems are beyond budget (>40k€), I’m considering alternative combinations.
Would you recommend LT‑500 + Garmin 24xd, LT‑500 + LT‑300, or LT‑500 + Furuno SCX20 (primarily for LT calibration and used mainly as a GPS)?
 

Yes, agreed, FOG aren't cheap!

Hard to advise the best combination to go for, but published specs are very interesting...
Static hdg: LT-500 +/-0.5, SCX20 +/-1.0, MSC10 +/-2.0
Dynamic hdg degrades a little bit for the LT-500 to +/-1.5. But still better than the Garmin unit.

Hardly encouraging accuracy for a 'GPS compass'! Not surprising for such a short baseline, and there has to be some sort of failover in these units or some seriously good kalman filtering to maintain a good gps fix.

So, a well located and swung LT-500 *should* provide better accuracy than the Furuno and Garmin units?

Here are some comparisons of a high grade SBG Ellipse D vs a couple of magnetic sensors from a transatlantic crossing - the mag sensors falling within the +/- 2deg spec that the cheaper GPS compass units are claiming. Admittedly the P9 was not swung pre start, and a large change in magnetic dip etc over a 2600nm race.