Recommend a 900 ohm low capacitance primary antenna connection. Isolation: Less than 6pf (3-4pf typical) inter-winding capacitance for minimum common mode transfer, and best ground independence.
Use a SO-239, for 50 ohm coax matching, or a F type fitting for matching 75 ohm coax.
Flag, Pennant, and Delta antennas, in order to receive low angles, need to be decoupled from ground to achieve ground independence.
Ground independence requires common mode signal decoupling of the coax cable shield. This is done by minimizing the matching transformer primary to secondary capacitance. A BN-73-202 binocular core, with low capacitance windings, can provide the needed isolation.
With the coax cable buried, or on the ground, a common mode choke may not be necessary.
Avoid metal, metal enclosures of the matching transformer as this can increase transformer winding inter-capacitance.
A small strong plastic box can provide transformer protection in most weather events.
As per Earl, K6SE (sk). The Delta receiving antenna has been the favorite of many DX-peditions, requiring only one non-metallic support at the top apex. The lower corners are typically fastened with ropes to tent pins that can be easily relocated to change antenna direction.
eham K6SE delta-FO0AAA antenna info
Flag, Pennant, Delta antennas operate with low signal levels. A 15-20 db gain preamplifier, usually located in the radio room, is necessary. The preamplifier in your transceiver is not adequate in gain, although it may help in conjunction with the external one.
Use insulators where the transformer and termination resistor connect, to take mechanical strain away from components.
For rotatable flag, pennant, delta antennas. Use a light weight support rod, such as fiberglass, from the antenna mast to the transformer for physical support of the transformer and coax cable.
Reception direction. If you are standing by the termination resistor, reception is from the direction of the transformer.
Any problem with poor reception, and/or poor front to back is most likely coupling to the transmit antenna. Transmit antenna detuning may be necessary. A relay may need to be installed at the transmit antenna feed point to disconnect the coax, or to disable/change other element tuning components while receiving.
A deep null on the back of the antenna is useful for interference control.
Typical terminations resistors are, 903 ohms for point terminated Pennant antennas, 945 ohms for Flag antennas, and 948 ohms for Delta antennas.
Avoid using heat shrink wrap over termination resistors. Protective coverings are not necessary.
Increased common mode decoupling of the coax cable was often accomplished by addng a coil of many coax turns, beyond the matching transformer, where the coax first met earth ground. As time passed the number of turns were reduced by adding ferrite cores.
Now a popular choke is constructed by winding 6-8 turns of small diameter coax in a 6 inch diameter coil and held together with plastic ties. One mix 31 ferrite 'clamp on' core Amidon 2x31-1081P2, or equivalent is installed over the windings.