Monthly Archives: March 2015

Avstörning av “Hembioanläggning”

En granne skaffade en ny “Receiver” av typen SONY STR-DN 1050 till sin “Hembioanläggning”. Jag hörs kraftigt i den vid sändning. En tidigare “Receiver” hade inte alls det problemet. Avståndet från antennerna är ungefär 80 meter. Uppskattad fältstyrka är klart under 3 V/m. Störningen hördes i “Surroundhögtalarna” dit de längsta kablarna gick. De högtalarkablarna lindades 5 varv i en FT-240-77 ferritkärna från Amidon. Samtidigt kopplades en skarvsladd in mellan vägguttag och samtliga enheter. Den var också lindad 5 varv på en likadan kärna. Störningarna var kvar, men hade ändrat karaktär. Vid prov att koppla från kabeln till TV-antennen försvann störningen. En kabel med en galvanisk isolator kopplades in i antennledningen (anm 1). Det återstod en svag störning. Vid kontakt med SONY support säger dom bara att receivern ska återställas till fabriksinställningarna. Hur det ska kunna få bort EMC-problemet har de inte kunnat förklara.

Ett filter för högtalarledningarna ska tillverkas.

Mätningar gjordes på en koppling enligt figur 1.

Fig.1

Filtret består av 7 ferritkärnor FT-140-77 lindade med ca 2×1 meter lackerad 1 mm koppartråd. En drossel för varje högtalare. Det blev ca 21 varv. Subwoofern ansluts med speciell kabel, så den får lindas på en stor FT-240-77-kärna.

Uppmätta data.

Frekvens MHz U1 Volt t-t U2 Volt t-t Dämpning 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

14,1 38 1,1 31

18,1 34 1,1 30

21,1 30 1,2 28

24,9 25 1,1 27

28,1 23 0,37 36

Försök gjordes för att hitta sämsta möjliga dämpning inom frekvensområdet. Det gjordes genom att variera frekvensen och belastningsimpedansen vid U2. Impedansen vid U1 hölls hela tiden till 50 ohm. Minsta dämpning uppmättes vid 25 MHz till 20 dB.

För att minimera risken för serieresonanser har även drosslar med ned till 5 varv provats, men dämpningen har över lag varit mycket sämre. Man får förmoda att förluster i kärnmaterialet är viktiga för dämpningen vilket är viktigt i den skarpa uppkopplingen i en odefinierad högtalarledning med en okänd impedans i förstärkarens utgångssteg.

Anm 1: Det visade sig senare att dämpningen av common mode-strömmar med den galvaniska skiljaren var mycket låg på kortvåg, ca 5 dB. Därför lindades en antennskarvsladd genom en ferrittoroid och seriekopplades med antennen.

The gain of the FB-53 tribander and influence from the 30/40-meter dipole

In order to ascertain the extent to which the dipole for 30/40-meter affected tribander I performed a number of measurements. These were conducted during October 2014, and were limited mainly to the 20-meter band. The results can be summarized as follows:

1. With the dipole along the radiator and the dipole coax shorted in the lower end
* -3 dB relative to a reference station.
* -2 dB relative to a reference dipole.

2. With the dipole along the radiator and the feeder terminated with a capacitor for SWR = 1 on the tribander.
* The -3 dB compared with reference dipole. (1 dB worse than with shorted coax).
* In direct comparison with shorted coax the signal is 3 dB less with variable capacitor. (Does not agree with the measurement to reference dipole).

3. Failed to change the F / B ratio by shifting between the capacitor and short circuiting.

4. With the dipole along with the radiator and dipolkoaxen closed with dummy load of 50 ohms and 13% dumped effect (of what is fed to the FB 53an).
* Difference = 0 dB compared to referensdipol (compensated).

5. With the dipole along the boom.
* +2 dB relative to the reference station
* +3 dB relative to the reference dipole.

That is: The Gain of the tribander is measured to 3 dBd.

Antenna for 40 m

The antenna for 40 m is a dipole inside two 12 m fiberglass poles from Spiderbeam. The outermost section is not used. It is mounted just below the tribander at about 21m.

The 40 m dipole has been shown to have a negative impact on the FB 53 when oriented parallel to its radiator. It is therefore currently oriented along the boom of the tribander.

See the post about the influence between different antennas.

My antenna for 10, 15 and 20 meters

UPDATE October 2017:

2017 October 15

Today the rebuilt radiator for the tribander was put in place. The traps were removed and there is now a full size dipole for 20 m made of aluminium from scrapped tubing. For 15 m there is a wire dipole erected 15 cm above the 20 m dipole and fed with a pair of copper wires. The dipole for 10 m is another 15 cm up and fed with 400 ohm ladder line. All dipoles are connected to the common original voltage balun from the FB-53.

The whole device was adjusted for resonance at a height of about 5 meters with a MiniVNA PRO connected via Bluetooth to my Android phone.

When the radiator was in place it was swept from the shack with the length of the feeder (34.5 meters) removed. The most spectacular change was for the 20 m dipole. It was set for minimum SWR at about 14050 kHz. When in place in the beam the frequency for minimum SWR had moved to 14650 kHz and resonance was now at 14350 kHz. When I measured the length of the dipole at ground it was 2×5.0 m and not 2×5.2 m as I had simulated for a similar three element beam. But I didn’t believe it would change that much. The SWR is acceptable at the band edge so won’t take it down to change the length.

The 15 and 10 meter dipoles didn’t change that much but the overall SWR on 15 is on the high side all over the band.

SWR numbers:

1.86:1 at 14000 kHz falling to 1.60:1 at 14350 kHz with a minimum of 1.44:1 at 14650 kHz

1.54:1 at 21000 kHz rising linearly to 3.10:1 at 21300 kHz

1.67:1 at 28000 kHz with a minimum of 1.56:1 at 28170 kHz and then rising to 2.20:1 at 28500 kHz.

I expect the gain of the beam on 20 to increase from the earlier measured figure of 3 dBd to about 4.2 dBd as a result of the “lossless” radiator.

The possible increase of output power to 1 kW due to the trapless radiator will give a boost of the signal with 1.5 dB on top.

Previous text:

The antenna for 10, 15 and 20 meters, is a FB-53 tribander from Fritzel with 7.3 m boom length. It’s approximately 21.5 m above the ground.

Measurement data for FB53 with the radiator and parasitic elements extended 2x3cm at the ends. Resonance at 14 MHz lowered about 120 kHz:

The gain over a dipole on 20 m has been found to be about 3 dB on the CW portion. The measurement was made with a reference dipole and Reverse Beacon stations on the US East coast.
Standing wave and F/B ratios below.
Measuring antenna was a delta loop at a distance of 100 m and height above the ground about 4 meters.

Using WSPR to check reciprocity

WSPR ( Weak Signal Propagation Reporter ) is a mode created by K1JT ( Nobel Laureate
in Physics ) . The measurement results can be sent over the Internet to a common
server that presents the results in an Excel friendly format . The stations transmit 
and listen by turns and all results are uploaded . It may look like this . 
Signal / Noise level specified relates to a bandwidth of 2.5 kHz .

A site about HAM radio

by SM0BRF