Here is their website
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As there are multiple models, you're going to have to be a lot more specific. Precisely which one did you get? I'm guessing the SWL model.
The PAR has a set of connections that allow you to change the configuration of how the antenna is grounded or strapped- it doesn't appear that the Dutch antenna has that. The Dutch antenna is using an unun - I am pretty sure the PAR isn't. On the other hand, you get roughly 70 foot of wire from the Dutch antenna - the PAR, as supplied, gives you 45 foot. Before you can do any comparisons, the 2 lengths of antenna wire need to be the same..
But we're jumping the gun here. You haven't said anything about what radio you are using, how long you've compared the 2 antennas, are the setups the same (same height, same coax, etc.), what band(s) you are doing the comparison, at what times, did you ground both transformers?....
You get the idea. You need to compare over a fairly long period of time, across multiple bands and conditions. It's quite likely the difference is in the transformer
It's anecdotal in nature; let's put some science to it.;..Mike