I’ve been a bit sceptical about the balance of the military telephone cable called DL1000 in Sweden. It almost looks as if one wire is wound around the other rather than two twisted wires. So I made a measurement as outlined in the sketch below while listening on strong signals:
As reference I connected both wires in parallel connected directly to the measurement receiver.
The results were:
Frequency Common mode rejection
7 MHz 25 dB
3.5 MHz 40 dB
There was no difference with and without the load resistor R.
So the telephone line is OK as a feeder for receiving antennas on 80 and below as regards to common mode pick up but doubtful on 40m.
I was using a 50m length of DL1000 telephone cable with a transformer with binocular BN73-202 at each end with a turn’s ratio of 2:3. There was a MINI VNA Pro used in transmission mode connected to the transformers.
Attenuation in the transformers:
Attenuation in transformers plus 50 m of DL1000 telephone cable:
I’m replacing my Beverage feeding system. The relays in the switchbox was powered through the feeder which was 40 m of buried RG-6 coax plus 70 m of military phone line in the trees. I had problems with noise from the relay voltages so now replacing it with buried outdoor UTP cable feeding the relays separated from the RF feeder.
The impedance of a UTP pair is 100 ohms and measured attenuation over 100 meters was as follows:
1.8 MHz 1.5 dBs
3.5 MHz 1.7 dBs
10.1 MHz 2.6 dBs
I took the transformers from the old 70 ohm system and measured the 50 ohm SWR all the way through 100 m UTP to a 560 ohm resistor in place of the Beverage wire:
The SWR was 1.35 at 1.8 MHz, 1.05 at 3.5 MHz and 1.55 at 10.1 MHz
Today Oct 4, the new beverage feeding system is up-and-running. Works as expected but the ground lead is too long picking up too much signal, especially on 40 and up. Had to move the relay unit from one tree to another. Will try to improve that.
Today November 8 I improved the ground with an extra ground stake. There is also a new NE wire running at 65 Dgs. For the moment 100 m long and unterminated.
On 21st of December 2016 local K-index was 8 (with 9 as theoretical maximum) with severe aurora. Strange things happened. Sort of sporadic E (or maybe sporadic F) was formed by the strong radiation. So had a QSO with W9YXX in Indiana on 20, late in the evening with 599 signals. Normally the band closes early. At such occasions the propagation is very patchy. I got a 31 dB RBN spot from WZ7I and a 27 dB spot from K3LR. No spot from anyone else in Europe or anywhere. I was the only EU station heard at his end he was the only station heard here except for C91PA who was 59 on 20, SSB. The noise was virtually zero with the needle stuck at the bottom stop.
Part of the QSO with W9YXX:
So great fun in spite of non-existing normal propagation
Tänkte prova 30m-tillsatsen för min A3WS. Den har legat och väntat i garaget i kanske 15 år. Filosofin har varit att passa på och montera den när det uppstod ett problem på beamen och jag skulle bli tvungen att ta ned den. Nu har ett fästband som hållit koaxen mot bommen gått av. Dags att agera.
Det visade sig bli ett större jobb än vad jag trott. För att kunna ta ned WARC-beamen måste jag ta ned min dipol för 40m och min trebandare FB-53. Jag tillverkade en linbana enligt tips på nätet. Det visade sig vara lättare sagt än gjort att få ned antennerna. Allting trasslar sig med allting och det som ska fungera i teorin har allvarliga brister när det kommer till verkligheten.
Idag har jag i alla fall fått ned 7 MHz-dipolen och FB-53an. Återstår A3WS.
Efter ett par veckor sitter alla antenner på plats. 30-meterstillsatsen på WARC-beamen går förträffligt. 25 meters höjd verkar passa den bra.
FB-53an har sänkts i frekvens på 20 meter till 14070 kHz. I original ligger den på 14225 kHz. Det förbättrade SWR och F/B-förhållandet på CW-delen. Dessutom monterades 3 cm långa pinnar före trappsen på den närmsta 10/15-metersreflektorn för att försöka förbättra F/B-förhållandet på CW-delen på 10 meter, men det verkar inte ha haft någon större efekt.
Inför lågbandssäsongen har en 160-metersdipol hängts upp och ett parasitiskt element har satts parallellt med befintlig Invvee-dipol. Den antingen direktor eller reflektor genom att ändra längde ett par meter. Riktningarna är SV eller NO. Dessutom finns en inverted vee-dipol med bredsidan NV/SO.
On August 14, 2016 in the afternoon these two antennas were run against each other at SK0QO’s QTH on Gålö South of Stockholm. They were mounted on separate masts about 18 meters above the ground with water in front in a northwesterly direction. The test was done using the Reverse Beacon on 20m towards North America. The power was 100 watts.
Receiver A3S dB SNR spots PRO96 dB SNR spots
W1NT 11, 9 9, 11
W3UA 19, 23 16, 23
KM3T 19, 20 17, 22
K1TTT 6 5
This gives that the A3S was on average 1.5 dB stronger than the PRO-96
A neighbour bought a new “Receiver”, SONY STR – DN 1050 to his “home theater”. I was making a loud noise in his loudspeakers when I was transmitting. His old “Receiver” had no problem. The distance from the antennas is approximately 80 meters. Estimated field strength is well below 3 V / m which is, to my knowledge, the field strength a consumer equipment should withstand. The numbers are as usual not accessible to the man on the street. The disturbance was heard in ” surround speakers ” which had the longest lines.
In an attempt to cure the problem the speaker lines were wound with 5 turns in an FT 240-77 Ferrite core from Amidon . At the same time extension cord with an equal core with 5 turns was connected between the wall outlet and all units. The disturbances remained, but had changed character. If the antenna was disconnected from the TV digital box, the disturbance disappeared. If a galvanic isolator coupled into the antenna line a weak disturbance remained (Note 1).
Upon contact with the SONY support their only advice was to reset the Receiver to factory settings. How that should be able to cure the problem, they could not explain.
An EMC filter for common mode currents was made for the loudspeaker lines. It is made up of 7 FT-140-77 ferrite cores from Amidon. One for each loudspeaker. The Subwoofer is connected with a special line so it must be winded on a big FT-240-77 core.
The attenuation on the different amateur band was measured.
The measurements were made according to picture 1 below, with my IC-735 as a signal source.
Frequency in MHz U1 Volts pp U2 Volts pp Attenuation dB
1.8 37 0.2 46
3.5 38 0.25 44
7.0 37 0.23 42
10.1 38 0.28 43
14 38 1.1 31
18 34 1.1 30
21 30 1.2 28
24.9 25 1.1 27
28 23 0.37 36
In an effort to try to find a point with the lowest attenuation, the frequency was varied and also the impedance at U2. The lowest value found was 20 dBs at 25 MHz.
At a later point, it was discovered that the attenuation on shortwave for that thing was only 5 dBs. Therefore a new extension with a ferrite toroid with several turns was made.
A line filter was made:
The power cord was winded 7 turns on a ferrite #33 core. 15 turns on line and neutral on a FT-140-43 core and 4700 pF ceramic capacitors.
In order to find out the extent to which the dipoles for 30 and 40m affected the performance of the tribander, a FB-53, a number of measurements were performed. These were carried out in October 2014, and were limited mainly to the 20-meter band. The dipole was mounted about 50 cm below the tribander.
To perform the test I was using a reference dipole a few meters at the side of the beam when beaming North America and also a reference station with which there had been several measurement series over the years comparing the FB-53 Yagi with another tribander. On the average the FB-53 has been 2 dBs better than the other tribander towards North America during afternoons.
The comparisons were made by extensive number of Reverse Beacon spots from the North American East coast and averaging a large number.
The results can be summarized as follows: With the 30/40m dipoles along the radiator of the tribander and the coax from the dipole shorted at the lower end
-2 dB compared with the reference dipole.
-3 dB compared with the reference station.
With the 30/40m dipoles along the radiator of the tribander and the coax from the dipole tuned at the lower end with a capacitor for SWR=1 on 20m
1. -3 dB compared with the reference dipole.(1 dB worse than shorted coax).
(It was possible to change the F / B ratio by shifting between the capacitor and short circuiting.)
With the 30/40m dipoles along the radiator of the tribander and the coax from the dipole connected to a 50 ohm dummy load at the lower end.
13% of the power fed to the tribander was dumped in the dummy load.
0 dB compared with the reference dipole.
With the 30/40m dipoles along the boom of the tribander
+3 dBs compared with the reference dipole
+2 dBs compared with the reference station. No interaction between antennas.
The proximity of the 30/40m dipoles to the tribander severely deteriorates the performance of the FB-53.
A second finding is that the gain of the FB-53 is 3 dBd on 20 m.
Would anybody be interested in exploring signal path reciprocity for shortwave communication? Or rather changes in reciprocity over time. It sometimes happens that for a period of time the path to a distant station seems to be more or less unidirectional. And I’m not talking about different noise levels but actual signal level.
The ionised plasma together with the Earth’s magnetic field will twist and deflect radio waves travelling through it making the path more or less non reciprocal.
I’ve been using WSPR to measure the reciprocity between SM and North America and it indicates that there at times could be a difference of up to 10 dBs. But there is a problem using WSPR. The output is not signal strength but SNR. On higher bands the QRN level is fairly constant over time, if not beaming into the sun, but there could be local noise or sudden QRM from say RTTY stations. At my end I’ve solved that by listening to a local station some tenths of km away and using that signal as a reference (the difference over a 24 hour period was very little). The DX station though did not use that feature.
The means of measuring the reciprocity is open to discussion.