First DX Signals Of The New Season - And A Comparison

I rarely hear any Trans-Atlantic DX here in August. My northerly location is of course to blame. Last night though, the ususal eastern North America stations were heard with ok signals, such as 1200-Ottawa, 1500-Detroit, 1510-Boston, 1520-Buffalo, 1540-Toronto and 1600-Boston together with quite a few others (including rather surprisingly Pulse 2 from Huddersfield on 1530). The first signal from Down Under was heard Friday evening with presumed 1620-Sydney with Arabic music.

Tonight's DX was somewhat noisy as there were frequent static crashes from thunderstorms somewhere. This gave me the opportunity to compare how the AGCs of the Excalibur software and SDR-Radio handled the noise. Generally there was a noticeable difference in favour of SDR-Radio. Nowadays with SDR software, AGC settings can be adjusted ad infinitum, but at least when it comes to out-of-the-box settings, SDR-Radio was the winner.

Antenna Preparations II

340-degrees beverage daytime noise level. The peaks are semi-local Russian stations (and the very local  "BV" NDB on 399 at extreme left)

The 340-degrees beverage (Western North America) was put up today. Unlike the other beverages it is lamp cord fed, not Twinax, and while the noise floor is at the same ultra-low level as the 50 and 310 degrees beverages, there are a few local noise peaks though not above -115 dBm. The jury is still out on the question should we replace the lamp cord with twinax.

This Is What I Call A Quiet Location

Actually, I have never experienced a noise level as low as today. China Radio International 1323 is 90 % readable at a signal level of 0.37 uV in AM mode, and 100 % readable at 0.6 uV. It doesn't get much better than this. Beverage 500 meters at 50 degrees, Twinax feed line.

Antenna Preparations

The 50-degrees Pacific beverage was set up last weekend, and erected to an average of 1.2 meters today. I also set up the 310 east North America beverage, but decided to keep the lamp cord feedline for now since the thought of rolling out 175 meters of thick and heavy Twinax was discouraging.

When I connected the 310 there was practically no signal at all. The observant reader will have guessed that the feed line was at fault. I didn't at first, so I spent a few hours in total confusion. This year rodents are exceptionally plentiful, and it appears that the seasick-green lamp cord was mistaken for food by the voles who thrive around the house. So I decided to roll out the Twinax anyway. The endless hours at the gym finally paid off. And the 310 is now in excellent shape, except I have to elevate it from the ground.

I think this calls for a Heineken on the balcony. Still a bit early in the season for any real DX.

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Balanced Feed Line - Replacing Lamp Cord With Twinax

Observant readers will know that last year, we replaced our old coax feed lines (mostly RG-213 and RG-58) with cheap "Lamp Cord". Using balanced feed lines instead of unbalanced proved to be an immediate success in terms of noise reduction and flexibility. The cost was the need to put a 100:50 ohm transformer into the feed line before entering the 50 ohm receiver antenna input. Though if you didn't, you wouldn't lose more than a few dB.

This summer, we purchased two 1000-ft rolls of "real" balanced feed lines, namely Twinax. It is not lightweight and flexible like the lamp cord - actually it's only a bit thinner than RG-213, but well screened and protected from precipitation, salinity, temperature changes and rodents.

A brief test run last evening with the 50-degree, 500-meter beverage proved that Twinax is indeed the best solution. Some unidentified local noise sources were greatly reduced, otherwise the noise picture in general was the same. I also noted that signals coming perpendicular to the 50-degree beverage were reduced substantially. Indicating that the lamp cord compromised the beverage's side nulls. There was a slight improvement in signal levels alongside the beverage lobes as well, but this could be attributed to the Twinax test being done five minutes later than the lamp cord test (with a declining sun).

Summary: The lamp cord is an excellent feed line for beverages (and other antennas as well). The Twinax is a superior feed line.

Lamp cord feed line

Twinax feed line. Murmansk stations on 657, 1134 and 1521 are attenuated compared to the lamp cord. Higher signal levels elsewhere.

Twinax

The Clifton Labs Z1501 Active Antenna - Pt 4 The 3 Meter Whip

This morning I replaced the 1.5 meter whip with the 3 meter whip. On SW, the difference was significant, with my semi-local Radio Rossii 5930 increasing 10-15 dB in gain. On MW however, there was only minor gain improvements as Rossii-657 increased its strength by only 2 dB.

This concludes the test of the Clifton Laboratories Z1501 Active Antenna. I will most likely dismantle it from my Kongsfjord QTH and erect in in a tree outside my apartment in Vadsø. It will be interesting to see how much it will be affected by the usual noise a residential area will produce.

The Clifton Labs Z1501 Active Antenna - Pt 3 Properly Erected

The next step was to find a better location for the antenna. I erected it on a pole around 30 meters away from the house, and prepared the necessary RG-58 coax. Still with the 1.5 meter whip, I mounted the enclosure at around 2 meters, so the total height of the antenna is 3.5 meters. Mounting it higher will increase its gain.

Both the noise level and signal levels improved considerably. As can be seen below, the antenna appears to have  equal sensitivity all the way up to 30 MHz. I didn't compare with the Mini-Whip this time. At the time of writing, 90 minutes after sunset, it seems to work well on MW with a noise floor around -120 dBm.

Weather permitting, I will erect my 310-degree beverage tomorrow. It will be interesting to compare noise floors and signal levels. I will also replace the 1.5 meter whip with the 3 meter whip to see how much gain increases.

Already at this stage though, the Z1501 has proved to be an excellent all-round antenna, both with regards to coverage (since it is omni-directional) and frequency range.

The Clifton Labs Z1501 Active Antenna - Pt 2 Initial Tests

I didn't have enough coax at hand, so for the first test run, the Z1501 was put up with the 1.5 m whip alongside the house wall. Not a favourable position with regards to RFI, but enough to see how (and if) it worked, and to make a brief A-B test with the Mini-Whip.

It has gain all right. I feared that the semi-local Loran C transmitter (250 kW on 100 kHz 14 km away) would make trouble when I connected the Z1501 to my Winradio Excalibur SDR. The Excalibur has no band pass filters or preselectors, so in principle it is wide open.

I was right. I got ADC clipping and needed to attenuate 12 dB to get rid of it. I assume though, that conventional receivers with band pass filters or tracking preselectors will not be affected. Anyway I am used to Loran C trouble, so I have a suite of 100 kHz notch filters, one of which was inserted between the DC Coupler and the Excalibur. Loran C gone.

To compare with the Mini-Whip, I mounted the latter at the same height as the Z1501 enclosure and ran a few tests.

Mini-Whip MW Response 

Z1501 MW Response

The difference in this daytime test (almost no stations audible) is significant. The 1449 Radio Rossii signal is 15 dB higher on the Z1501. But keep in mind that the price tag is at least "15 dB" higher too. It's a bit like comparing a Ferrari to a Fiat 500.

And I still haven't put the 3 meter whip on...

The Clifton Labs Z1501 Active Antenna - Pt 1 The Hardware

Conventional wisdom says that MW DX-ers use beverages whenever they can. And if they can't, they use loops of various sizes and properties. So what about whips? Noooo, serious MW DX-ers don't use whips. Whips are for FM or VHF. Only if nothing else works or is possible to erect (including a five cm ferrite bar), will a serious MW DX-er even remotely think about mounting a whip.

Time to think again. Whips with good performance have been around a while. Many NDB DX-ers have successfully used Roelof Bakker's "Mini-Whip", an excellent proof that size doesn't always matter. I've had the Mini-Whip myself a couple of years, and although it has never outperformed my beverages and QDFA, it is an excellent device.

For quite some time I have wondered about purchasing another whip. This summer I finally decided to go for it - not that I really needed it (and I don't think it will outperform my beverages and QDFA), but I was curious if it could perform even better than Roelof's mini antenna.

The Z1501 is sold with either a 1.5 m or a 3 m whip. I chose both, since it was only USD 16 extra.

The Z1501 is an electric field responding “active” antenna, employing a high impedance field effect transistor input stage to efficiently couple electromagnetic field from a physically short antenna to a low impedance (50 ohms) load. The most effective frequency range is 20 kHz to 30 MHz. The size of the weatherproof enclosure is 114x63x25 mm mounted on a larger mounting flange. It has a female BNC connector for 50 ohm coax feedline.


In-house is a DC coupler which delivers 9-24 VDC to the antenna. It can also be used with other active antennas - I have used the Mini-Whip with it with good results.

Enclosure and mounting flange. BNC out to the left.

Telescoped whips, 1.5 and 3 meters

DC Coupler back panel

DC Coupler front panel with green LED

The Z1501 is bought as a kit or assembled. Knowing how soldering limitations, I opted for the assembled version.

So how does it perform? We will soon find out.