Albeit not exactly a delta loop and neither for HF but for the 6 meter band, following my experiences.
I was missing a 6m antenna and therefore was looking for a simple to build antenna to experiment with during the 6/10/12m challenge. I found a very simple to build delta loop that shows about 50 Ohms at the feed point, by changing the aspect ratios (description in German: Delta-Loop für 6m mit einfachsten Mitteln › HAMSPIRIT.DE).
Then I thought it would be even better (in terms of performance) to build a quad, or for easier construction a diamond shaped quad. DK7ZB has an interesting idea (scroll down to the Rhombic Loop): The DK7ZB Oblong.
Yesterday it looked like I should be able to activate a summit WX-wise in the nearby black forrest, so I hurried in building the loop in the morning. Fortunately, all material was by hand, so I needed less than half an hour to build it.
The first thing after arriving on DM/BW-293 was tuning the loop for resonance and after two cut-offs, my fingers were freezing and it was good enough for a quick try.
Unfortunately, no one was answering my SSB calls on 50.285 MHz, so I have no idea if it really performs. I also gave up after some minutes calling, since no mobile network was available, so I had to use APRS to send a spot that needed further precious time in the cold.
I will definitely try it another time, by tuning the loop more exactly, in warmer weather and easier spotting possibilities.
Even I could only make one local (65km) 10m contact (out of a total of 24) by using my compact EFHW antenna (better on 10m than my standard EFHW and shown at SOTLAS), the activation was great fun with the first snow in this winter season and I definitely have learnt new things!
Update and note to other 6m/50MHz activators in DL:
A kind German ham informed me today that in Germany one can only use the 6 meter band from a fixed station, but not with a portable station, at least until the end of this year.
Official reference: https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Telekommunikation/Unternehmen_Institutionen/Frequenzen/Amateurfunk/AmtsblattverfuegungenAFu/Mitt1112020.pdf?__blob=publicationFile&v=11
I was aware that only horizontal polarization is allowed in Germany. This was another reason, why I built this diamond quad, fed from below. I informed myself before building the antenna by checking the German band plan from the DARC (German Amateur Radio Club, see https://www.darc.de/fileadmin/filemounts/referate/vus/bandplaene/VHF_Bandplan_6_m_Mai_2020.pdf), but the above mentioned restriction is missing in this leaflet.
I assume in the following days there will be an update in this matter, since the current rules are only valid until 31.12.2020.
73 Stephan