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Activdipole Stampfl X-One

 

In 2019, I tested the first active dipole from Heinz Stampfl (HB9KOC). This antenna was, so to speak, the revival of the forgotten active dipole. Why this interesting antenna type was forgotten is a mystery to me. There was only talk of the "magnetic loops" and their excellent reception performance. And rightly so, of course! The Stampfl active dipole found many enthusiastic fans after its market launch. The reception was and is excellent for the small dimensions of the antenna. Unfortunately, it was only sold as a kit, which obviously made it difficult to distribute the antenna.
Now Heinz Stampfl is presenting the successor to his first active dipole. The X-One! This antenna is now (almost) ready to be assembled in the hands of the SWL.

 

The most important technical data of the X-One
-- Frequency range: 90KHz - 150MHz (usable from 10KHz)
-- Polarization: Horizontal
-- Large signal strength IP3: 28dBm - IP2: 66dBm
-- High selection efficiency
-- Excellent common mode rejection
-- Power consumption 270mA / 12V
-- Mast mounting: 40-60mm
-- Total length of the antenna: 0.8m
-- Weight: approx. 900g

Scope of delivery:
-- X-One
-- Bias Tee DCW-1
-- DC cable
-- Banana plug
-- N to BNC adapter
-- Claw clamp

Unpacking, assembly

The X-One arrives largely assembled in a sturdy cardboard box. After inspecting the contents of the package, it's time to assemble!
Only the dipole elements, the end caps and the claw clamp need to be fitted. When fitting the dipole elements, make sure that the sealing surfaces on the gray polycarbonate housing are not damaged. Otherwise leaks may occur and moisture may penetrate the antenna housing.
The two O-rings on the dipole elements are also very important for tightness. These must lie neatly in the groove. A little tip at this point: If available, lubricate the O-rings with a little silicone grease. This keeps the rubber O-rings soft for a very long time. Then tighten the screws inside the housing. Be careful not to slip with the tool and damage the amplifier electronics. Unfortunately, a tool stop was forgotten during the manufacture of the dipole elements. This could have been two small milled recesses in the round bar so that a wrench, for example, could be used to tighten the dipole elements. Not everyone has a vice!
If you want to activate the FM lock, the jumpers J1 & J2 on the amplifier board must be removed. Make sure that the neoprene seal on the cover lies neatly in the groove. Then tighten the four corner screws. Done!

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Installation site and mast assembly

Ideally, the installation site for the X-One should have been determined in advance. This should be a quiet HF location, as far away as possible from domestic interference. The X-One is mounted on an aluminum, steel or GRP mast. The mast diameter can range from 40mm to 60mm. It is also important that the antenna is as free-standing as possible. Minimum distance to walls and trees approx. 4m. The installation height is essential and should be at least 5m. If the X-One is mounted higher than 10m, you should watch out for overload effects. If this occurs, the installation height should be reduced. The directivity of the X-One can be used to suppress interference. As with loop antennas, active dipoles are also directional antennas, primarily in the lower frequency ranges. The higher the frequency, the more the directivity decreases. The use of a rotor can be considered and increases the flexibility of the antenna.
If the mast is metallic, it should be properly earthed. The X-One itself does not need an earth connection because it already has its counterweight through the second dipole element. An active dipole is a symmetrical antenna.


Above: X-One
Below: Datong AD370 in a do-it-yourself housing.


 

The receiving direction of the active dipole. 90° offset to the dipole elements.

 

The appearance of the X-One

Admittedly, an active dipole with these disks at the ends of the dipole elements is unusual to look at, but nothing new in practice. If you look at professional active dipoles from Rohde & Schwarz, you will notice that certain models have such disks fitted.
Why these disks? These are so-called capacitors and are used to increase the capacitance and reduce the antenna size. If the capacitance increases, the voltage at the dipole elements also increases. This has a direct influence on the reception level.

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Chasing waves with the X-One

Test conditions
-- GRP masts
-- X-One superstructure height 5.5m
-- Installation height AD370 4.9m
-- Bias Tee the same for both antennas. Stampfl DCW-1
-- Coaxial cable Belden H155 for both antennas
-- Receiver Winradio Excalibur G33DDC
-- Elad ASA-62 antenna switch

I had the X-One in continuous operation for several months and was able to get a good picture of the antenna.
The first thing that stands out is the antenna itself! With the capacitors on the dipole elements, it looks very special. You could be forgiven for thinking that a Rohde & Schwarz antenna is mounted on the mast. Due to the thick dipole elements, the X-One is heavy compared to the competition, the Datong AD370. I compared the X-One with this tried and tested antenna, which is my reference antenna. The AD370 is significantly lighter and not as conspicuous as the X-One. However, the dipole elements are each 1.2m long and 2.5mm thin.
Such thin dipole elements have their disadvantages, especially in winter when there is snow. Then the thin dipole elements are literally pressed down by the weight of the snow. This does not affect the X-One with its thick dipole elements. It is made for this. The mechanics are super-stable and defy all weather conditions. Except for the round capacities at the ends of the dipole elements, which provide a surface for the wind to attack.

Very good active dipoles are now available. It is becoming increasingly difficult for testers to assess the reception performance of these antennas. The reception performance is often very close! Recording audio comparisons was almost not worthwhile in this comparison. The differences are only audible at very weak stations, if at all. Both antennas receive largely equally well. Differences are only recognizable at the turf. And only if you concentrate on the signal.
In the evening hours, when the sum signals increase and the levels at some stations rise above S9+30dBm, slight clipping was noticeable on the X-One. Intermodulation on twice the frequency was particularly noticeable with signals from the 31m band. The AD370 also exhibited this behavior. However, only at higher signal strengths around S9+35dBm and higher.
What the X-One can do much better than the AD370 is suppress common mode interference. This can be seen very well in the lower frequency ranges. Reception is significantly less noisy. As the frequency increases, the overall level of the X-One decreases slightly, which is noticeable with very weak stations in direct comparison.
Activating the FM lock has a slightly negative effect. The noise floor increases slightly. Depending on the frequency range, this can be up to 3dB. According to the manufacturer, this is due to asymmetries in the FM cut-off.


Always use headphones to listen to the audio recordings.
Second   0-10 > X-One
Second 10-20 > AD370

18.3khz
RDL Russian Navy
 66.66khz
BPC Time Signal
 153khz
Antena Satelor
 1170khz
R. Capodistria
 3485khz
Gander Volmet
 6290khz
Piratensender NL
 8957khz
Shannon Volmet
10051khz
Gander Volmet
 13020khz
Sound of Hope
 14670khz
Time Signal CHU
 21630khz
BBC Acension
 25000khz
Time Signal Colorado
 25900khz
BBC Talata Volondry
 28257khz
 Bake DK0TEN


 

Waterfall diagrams

Level differences between the two antennas are best seen in the waterfall diagram. The dark blue represents the background noise. The lighter the blue, the higher the noise floor. Basically, it can be said that the level differences between the two antennas are max. 5-8dB. The SNR (signal-to-noise ratio) can also be roughly derived from this. The more colored the lines (transmitter) are and the darker the blue, the better the SNR.

Waterfall diagram below:
For the first time I made such a 0-30MHz diagram with highest resolution. The JPG file is over 70MB in size. If you click on it, a new browser window opens with the section below. This is greatly enlarged. The 0-30MHz are displayed with a resolution of 1.5KHz. So you can see every detail in the waterfall. I recommend to open this file only with a fast internet connection. Otherwise use the spectrum sections below. The sections are each 4Mhz wide.

 

Waterfall chart sections:
 0 - 160KHz , 0 - 4MHz, 2-6MHz, 6-10MHz

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Waterfall chart sections:
10-14MHz, 14-18MHz, 18-22MHz, 22-26MHz, 26-30MHz

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Reception in the FM range and up to 150MHz

According to the technical data, the X-One receives up to 150MHz. The Datong AD370 should also receive up to 100MHz. Unfortunately, the topographical location of my home does not allow very good FM reception. Aircraft radio is just about possible. Anything above that is not suitable for comparisons. The X-One has therefore only been tested in this frequency range.
I made the comparisons with the ELAD FDM-S3/DCM.

 

Below is an almost 20MHz wide waterfall diagram of the VHF band. It clearly shows that the X-One receives much better than the AD370. It delivers the stations at a higher level with practically the same noise floor. In other words, better SNR.

Use headphones to listen to the audio recordings.
Second 0-10 > X-One
Second 10-20 > AD370

FM-89.0Mhz
300k-SWR4 FN
 FM-91.8Mhz
80k-SWR1
 FM-101.5Mhz
300k-SRF1
 FM-106Mhz
80k-Baden FM

 

The entire aeronautical radio band at a glance. Unfortunately, the radio activity was very poor. The X-One receives quite well here too. The AD370 drops off significantly, which is not surprising.


Conclusion:

The X-One stands out with its special look. It is robustly built and can withstand many a storm.
It is supplied as a complete antenna and thus saves many SWLs the annoying task of finding certain components such as housing, claw clamp etc.. Installation is therefore completed quickly.
In terms of reception, the X-One is one of the top active antennas. It impresses with very quiet and low-noise reception and is slightly superior to the AD370 in some reception situations. The large signal behavior on shortwave is not entirely convincing. With strong sum signals, intermodulation can be heard here and there on twice the transmitter frequency. If the FM lock is activated, the background noise increases slightly, which is a disadvantage.
The X-One does not deliver a brutal level and is therefore also suitable for cheaper receivers.
Reception in the FM broadcast band is good enough for normal requirements.

An all-round successful antenna!

posted: 21.02.2024

 

 

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