Henry Kolesnik. WD5JFR wrote:
"It seems that three antennas spaced about 1000 feet apart on an
equilateral triangle was a 100% solution."

Radio Free Europe relayed broadcasts from Munich to Lisbon by HF.
Satellites now make HF obsolete.

The point to point relay used one or more rhombics in Munich and three
in Lisbon for triple diversity reception. The three rhombics in Lisbon
may not have had optimum spacing. We had to clear cork and olive trees
to make room, but the recieved signals in them faded separately, in
spite of their side by side placements. We had apace diversity. All
rhombics were horizontal.

Frequency diversity was also used by transmitting on more than one
frequency in Munich. More than one horizontal rhombic was sometimes used
in Munich. Due to ionospheric polarization scrambling, no attempt was
made at polarization diversity.

Each receiving rhombic fed three or more receivers. The outputs of three
receivers were fed to an election box which selected the strongest and
least noisy signal while squelching all others in its group.

Henry mentioned, among others, the 51-J and SP-600 receivers. The 51-j
was incompatible with this mission. It had too many spurious responses.
We once tried to use one as a bridge detector at a transmitter site and
it was useless. The SP-600 has the front end selectivity required.

We used double sideband (AM) transmissions, but the SP-600`s had
selectable sideband responses which allowed us to supress interference
on one side of the carrier frequency.

These TDR systems worked like gangbusters.

Best regards, Richard Harrison, KB5WZI