The W2PM Mini Diamond Receiving Flag

Another nice receiving antenna…

This description is taken from the Pete’s W2PM posting into Topband reflector.

This antenna is very simple – it’s a mini diamond Flag – with a 660 ohm terminating resistor and a 16:1 transformer. It is the exact size of the so-called magnetic loops, – 5 ft per side, 20 ft total wire, and about 7.1 ft wingspan. It has classic Flag cardiodal pattern and, of course, pretty low output (-50 dB from what I recall). F/B is about 30 dB. I use it with a single preamp with good results. This antenna is quite easily rotatable as you can see (altho the standard 15 X 30 ft Flags have been made rotatable too as most of you know).

This has several advantages over the “mag” loop (for those on small lots) – it’s broadband 1.8 MHz past 30mhz; cardioid pattern with very nice null to rear, decent low angle take off (abt 32 deg) AND is simple – make it in minutes. I used 2 – 330 ohm resistors a binocular 16:1 transformer. I “potted” the resistors and xfrmr in epoxy.

I’ve since cleaned mine up – routing the RG-174 coax from the transformer to the center of the crosses, then connect it to a RG-58 run vertically down the mast.

Thanx loads to Earl K6SE for the design.73 Pete, W2PM


The antenna might look like this:

The W2PM Diamond Flag

The W2PM Mini Diamond Flag.

My NEC-2 analysis shows that it has:

Z = 670 + j51.3 SWR (800) = 1.21

RDF = 7.91

Gain = -43.5 dB

Takeoff = 36 deg. on 3.52 MHz with h=1 m (3.1 ft) above an average ground.

These data are quite impressive, taking into account that this antenna is extremely small (the same size as many others building “magnetic” loops). The low gain (read high attenuation) can be a problem – there is high demand on the transformer and common mode currents suppression, also a 30 dB amplifier is a must. Anyway, the radiating pattern looking very nice:

W2PM - vertical

The vertical radiation pattern. The takeoff angle is some 36 degrees.

 W2PM Horizontal

The horizontal radiation pattern. Note the nice cardioid with excellent F/B.

W2PM - 3D

The 3D radiation pattern of the W2PM Mini Diamond Flag.

The SWR response is flat from 1.8 to 4 MHz. A 1:16 transformer is used for impedance matching to a 50 ohm coax.

W2PM SWR response

SWR Response 1.8 – 4 MHz

W2PM Smith Chart

Smith chart

The figures above are valid with a 1:16 transformer wound on 3 stacked BN73-202 binocular cores (glued together) with 2 turns on primary (coax side) and 8 turns secondary (antenna side). A detailed transformer description is here.

Here are some photos takem from Pete’s archive:

W2PM front

Front view of the W2PM Mini Diamond Receiving Flag

W2PM overall view

Another view of the W2PM Mini Diamond Receiving Flag

W2PM matching transformer

The transformer

W2PM terminating resistor

… and the terminating resistor