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The MD300DX is delivered with 2x 2.5m long rods made of stainless steel wire rope. It can be flexibly attached to trees or non-conductive masts. The manufacturer recommends vertical installation because the active dipole offers all-round reception and delivers full performance. With the recommended vertical installation, however, there are some important factors to consider that hardly anyone knows. It is essential to ensure that no metallic masts are used. This is absolutely important when using vertically polarized active dipoles. If a metal mast with a short boom is used, resonances occur between the rods and the mast and the frequency response of the antenna is significantly disturbed. There are strong level increases or even signal cancellation. The cable to the antenna is also very important. The coaxial cable feed line must be at least 2 m at right angles to the rods. Otherwise you have the same effects as with the metallic mast.
Picture below: Comparison between a horizontally and vertically polarized active dipole on a metal mast with a 60cm long arm. The horizontally mounted active dipole (Datong AD370) shows a clean frequency response. So no reaction to the metal masts. The vertically mounted active dipole (MegaDipol), however, reacts violently to the metal mast. Distance to the metal mast around 70cm. Level increases and signal cancellations are the result.

Picture below. In order to be able to operate the MD300DX vertically, it must be mounted on a plastic mast. This is how a vertical active dipole is correctly built up.

In order to do my experiments and comparisons, I built the amplifier board of the MD300DX into a stable and larger housing in order to be able to use rigid antenna radiators. I used two 3m telescopic antennas from Buddipole. With this variant I can easily operate the antenna vertically as well as horizontally on a mast. The length of the rods can also be varied by inserting the telescopic rods.

Reception with the MD300DX (horizontally polarized)

The MD300DX was tested for reception performance for several weeks. I ran it horizontally for a while and compared it to the Datong AD370. As you can see in the picture below, the MD300DX is significantly larger than the Datong AD370, which is mounted on the rear arm. Overall, the reception performance of both antennas was very similar. There were differences mainly on the lower frequencies up to about 5Mhz. If the antennas were aligned accordingly, the Russian alpha signals could be received well on 11.9, 12.65 and 14.9KHz. The Datong brought the signals a little stronger, but noisy. In the VLF, long wave and medium wave range, the MD300DX was clearly ahead. The signal-to-noise ratio (SNR) was always slightly better than the Datong. The differences were small on the shortwave. The antennas could not be distinguished from one another. The MD300DX of the Datong could only pull away a bit from around 16MHz. The weakest signals, especially in the 11m or 10m band, came more clearly with the MD300DX or could only be heard with it.
There is a jumper on the amplifier board that can be used to increase the gain by 3 dB. However, the additional reinforcement brought no benefit. This is more intended for short rods.

Image below: The three alpha signals received with the MD300DX are horizontally polarized.

Reception with the MD300DX (vertically polarized)

Vertically aligned and mounted on a plastic mast, the MD300DX ignites the receiving turbo! The signal levels, especially in the lower bands, rise up to 25dB! Not every receiver can cope with such strong, almost brutal levels. Cheap receivers, especially the RTL-sticks, are hopelessly overwhelmed with this antenna. Even the Kiwi-SDR had to give up, as did the Airspy HF+ Discovery. These overdrive regularly in the evening hours. Only the Winradio G33DDC, Elad FDM-S3 and the Rohde & Schwarz EK070 coped with the strong signals of the MD300DX.
The reception successes in the VLF area were very interesting. With the MD300DX, the Japanese time signal JJY on 40Khz and the Chinese time signal PBC on 68.5KHz could be received here in Switzerland! That was very rare in the past. Thanks to the very good signal-to-noise ratio (SNR) that the MD300DX delivers, these reception successes are possible here almost every day. It continued on the long wave. Island on 207KHz was practically only audible with the MD300DX in vertical polarization. My rotatable loop also had to fit. The signal levels were very high on the long wave. RTL on 234KHz popped in here at times with S9+50dB. Some receivers are already reaching their limits. The medium wave continued in the same rhythm. During the day you could hear medium wave well because not many stations could be heard. The dance then starts in the evening. The medium wave is so full of transmitters, the channels are occupied several times and with very high signal levels that normal listening was not possible. For hardcore DX'ers ​​this is not a problem. New York could be recorded at 1130KHz at times. But there wasn't much more to it, because my location for America reception on medium wave no works well. In the medium wave range, the horizontally polarized variant is much more pleasant. On the shortwave it continued with the strong signal level, but was no longer so extreme. Nevertheless, there were stations in the 49m and 31m bands in the evening that brought around S9+50dB. About 20dB more than the horizontal variant.

The vertical polarization offers all-round reception. This is an advantage, but also a disadvantage! No disturbances can be hidden. With horizontal polarization, you can turn the antenna and thus hide certain interferers. If the MD300DX is operated vertically, it should be located far away from the house. Preferably in the open field. The horizontal polarization is not that sensitive in this regard. But that applies to every active dipole.

Conclusion:
The MegaDipol MD300DX has a very strong reception! If it is operated vertically polarized, it needs a good receiver that can handle its level. With her, receptions were possible that I hadn't succeeded until then. Horizontally polarized, it is more compatible with hobby receivers. But the most important thing is the signal-to-noise ratio (SNR). This is excellent with the MD300DX. The secret lies in the low gain and the extra long rods.

Highly recommended! A top antenna!

posted: 03.02.2021