Antennas may not behave as you believe they do.

If these assertions shock you or you are considering building up the hybrid antenna system kit please read all the background FIRST. This includes but is not limited to

If you are thinking of constructing this system, I strongly suggest first building the PreampA along with the Shack Board. This allows testing the construction process and also provides a tool for mapping a prospective location to verify suitably low common mode and near-field noise ingress to see if a proposed site merits committing to a traveling wave antenna and junction box as well. An Active Dipole using PreampA may suffice until other noise ingress problems are solved. There is yet another reason for building only the PreampA and the Shack board. That reason is that you may be able to completely avoid building up the PreampB and Junction to create the Hybrid antenna system and achieve the ITU curve C noise floor. If your location and siting effort indicates, it may be possible to use PreampA with a larger dipole, perhaps something on the order of 2 x 5m monopoles for a total of no more than 10m tip-tip.  At this length, the antenna factor may be good enough compared to the OpAmp noise to reach ITU "quiet rural" levels all the way to 30 MHz. An antenna like this requires a vertical support that is more visible so may be a problem with HOAs and such a system is no longer "portable" for mapping but if a suitably quiet location can be determined, it may be all that is necessary to create a high quality LF through HF receive system without resorting to a Hybrid system.  The visibility problem may be mitigated through hanging rather small diameter conductor from a support. With a larger dipole such as this, signal levels will also be higher which  might cause an overload problem that wouldn't be present with a smaller structure.   Whether or not going to a larger dipole is warranted and whether the continuation to a Hybrid system is merited will depend upon a particular site.

A QUCS-S:qucsator PreampNoise.sch model may be used to examine possibilities.  This is an in-process modeling tool so please let me know if there are errors, problems or if you know a better way to write this sort of model.

None of this is a "silver bullet" and there will only be disappointment if you don't understand how to deploy this hardware. For this system, signals and the propagated noise that you want to become dominant at your receiving system detector are small. This means that unwanted ingress, either from common mode currents or near-field sources must be kept smaller still, several dB below the hybrid systems levels. If you don't do this, your limiting noise will not be from what you believe to be your antenna system.

Because both antennas and preamps are differential, it is easy to verify that the intended antenna is the source of the noise. On an installed system, if shorting  the the two monopoles in front of PreampA or the differential connections from a traveling wave antenna connected at PreampB does not drop all signals throughout the spectrum 6-10 dB then you still have work to do! This is a test that cannot be done on a single-ended monopole (whip) system.

Even if your installation meets this test, you may still have near-field ingress, which is why you need to be able to calculate absolute noise power levels and  do site mapping. I suggest building up the dipole/PreampA + Shack PCB system first and using that to map a candidate location and polarity using a portable receiver that can view 0-30 MHz. Polarization is important here as it affects both take off angle and efficiency. Over typical ground going to (H)orizontal polarization will generally incur 6-8 dB additional attenuation at the same time the take off angle goes nearly vertical. Don't let this fool you but consider SNR not absolute levels.

It is very helpful to use a broadband SDR or spectrum analyzer to  view the entire range in one sweep. This permits discovering and learning about ingress that simply viewing a narrow slice of spectrum or a single amateur band may not reveal. Propagated noise is not 'bumpy' versus frequency. It is sometimes useful to listen to broadband demodulated AM, perhaps in a 10 kHz or wider bandwidth, to see if there is a noticeable mains 'hum' component that isn't obvious in USB or narrower modes. Many local noise sources operate from switched mode power supplies that are poorly filtered and AM detection can reveal harmonic lines from these. Propagated noise, often produced by lightning strikes around the world, has a different characteristic that it is useful to learn these differences and what to listen for.

Generally, surveying an area with the dipole vertically polarized while a few meters above the ground can help determine a potentially good location. After an available candidate location that shows the most promise has been found, using that as a more permanent location is a good place to begin. If subsequent noise measurement s indicate that it is merited, an LoE and PreampB can be installed their as well.  Count on this entire process requiring months or years!

An example of the HW pieces matches the block diagram above and looks like this picture which was taken before the same were sent off to VY0ERC near the magnetic North Pole

The preamps and the junction PCBs were placed inside PVC electrical boxes which can be made waterproof. The dipole antenna connections, the traveling wave antenna connections for PreampB are made at the ends of the respective boxes with the CAT5 cable coming out of the "T" arm and connecting at the ends of the Junction box/PCB. The common CAT5 goes from the junction "T" all the way to the Shack Board.

The shack board may receive either single pair connection from the "A" side, separate connections to a diplexer when also using the "B" side or, in the case of the Polarimeter described elsewhere,  connections to a quadrature network for extracting O and X polarizations from a quadripole antenna. The shack board pictured is an earlier version.

The housing for the Active Dipole Preamp accepts two 1m long .125" diameter stainless steel rods which are placed through PVC end caps. Contact to them is made by wrapping .5" wide sticky copper tape around the end of the rod and soldering a thin wire to the tape. The other end of the wire solders to one of the antenna pads on the PreampA PCB.

The PreampB housing is similar but with connections brought out from only one end. An intervening 5:2 turn balun is usually placed here to convert the 100 ohm differential impedance to something near 600 ohms. For each preamp, the RJ45 connector points toward the "T" where the CAT5 cable exits. Teflon tape can be used to ensure hermeticity. I found it a good idea to place a thin piece of thermal padding between the PVC bottom and the PCB to aid in extracting heat.

Typical 24 Hour WSPR spots from VYOERC and N6GN/K2 using a KiWiSDR receiver and the hybrid antenna system: