| AM Loop Antenna |
As I get older I keep getting tired when I keep watching TV, and recently listening to radio has become more common. My house is a two-story wooden building, but AM reception is weak in radio waves and there are many noises except for NHK 1 and 2. Especially I like Radio Japan of 1422 kHz and the frequency is high and radio waves are weak, so I can’t enjoy Japanese popular song satisfactorily. So I tried to make AM loop antenna and to improve reception sensitivity. As a result of fabricating four loop antennas including the kit, great improvement was seen in the reception state of any antenna. In addition, the inductance of the loop coil was found to be 213 μH to 276 μH, and the stray capacitance was found to be 15 pF to 26 pF. For the method of connecting to the radio, I tried the method of connecting the pickup coil directly to the antenna terminal and another method of fixing the loop antenna attached to the radio near the center of the AM loop antenna. As a result, I felt that the former was better. The more the pickup coil is away from the primary coil, the smaller the number of turns is, the clearer the tuning point can be found but decided by considering its sensitivity.
Many examples of production were found when searching "AM loop antenna" on the net. Although
it seems to be able to make it even as soon as I buy the material, the number of receivers in
my house is four, but there are only three variable condensers for AM on hand. Therefore, I
decided to buy one kit of Shamtec Electric (L-001) for research. It cost about 4,000 yen including
shipping cost but it will be cheap tuition fee as I will make 3 units later. Everyone can do
assembly according to the instructions. I used it with SONY 's stereo component (DHC-MD333),
but the reception condition has been greatly improved. Because I bought this component in
second hand, I didn’tt have the antenna attached, so I connected the pickup coil directly
to the antenna terminal.Well, the next is loop antenna analysis (inductance, stray capacitance, tuning frequency range). Circuit area: 40 cm x 40 cm, coil length: 1.8 cm, number of turns: close contact wound 14.75 times, coil pitch: 1.2 mm, coil copper wire diameter: 0.3 mm, variable condenser capacity: 20 to 300 pF, pickup coil: 2.75 times tightly wrapped with a vinyl cable with a diameter of 0.3 mm inside the coil. The inductance of the primary coil measured with the LCR meter was 213 μH. Next is estimation of stray capacitance. When the oscillation frequency was measured by connecting this loop antenna to my own L meter, the calculated value was 3.367 MHz, but actually it fell to 1.809 MHz. When the capacitor value of the oscillator was measured with the LCR meter, it was 10.5 pF, so the stray capacitance was calculated to be 26 pF from the oscillation frequency difference. As a result, the tuning frequency range was 604-1609 kHz, and it turned out that it was close to the feeling actually used. The NHK 1 at 594 kHz, which is slightly out of the tuning range, is originally very strongly entered, so there is no problem.
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Original work machine No. 1 was synchronously remodeled the spider coil type loop antenna made
long ago. The coil is a single-core cable for intercom, the variable condenser is 25 to 220 pF
air variable condenser for TS520. The reception condition was greatly improved when I used it
in Denon’s tuner (TU-1500) after completion. Although this tuner had the attached antenna,
I connected the pickup coil directly to the antenna terminal without using it. Circuit area:
40 cm x 40 cm, coil length: 2.8 cm, number of turns: 15 contact windings, coil pitch: 2 mm,
coil copper wire diameter: 0.5 mm, variable condenser capacity: 25 to 220 pF, pickup coil: loop
coil It is three times space winding of the 26th copper wire with a diameter of 0.45 mm on the
inside. The inductance of the primary coil measured with the LCR meter was 238 μH.
When connecting this loop antenna to the self-made L meter and measuring the oscillation
frequency, the calculated value was 3.185 MHz, but actually it fell to 1.900 MHz. From the
oscillation frequency difference stray capacitance was calculated to be 19 pF. As a result,
the tuning frequency range was 668 - 1556 kHz, and it turned out that it was close to feeling
actually used. Since NHK 1 at 594 kHz out of the tuning range is originally very strongly
entered, there is no problem.
My own machine 2 was made using cheap wood bought at the 100 yen shop. The coil is a single-core
cable for intercom, and the variable condenser is 15 to 150 pF polyester variable condenser of a
broken transistor radio. After completion, I used it with Onkyo’s stereo component (R-811M),
the reception condition was greatly improved. Although this component had the attached antenna,
I connected the pickup coil directly to the antenna terminal without using it. There is no point
in the color difference of the coil at all in relation to the handheld cable. The finished data
of the loop antenna is cross sectional area: 20 cm x 22 cm, coil length: 5.5 cm, number of turns:
28 contact wound, coil pitch: 2 mm, coil copper wire diameter: 0.5 mm, variable capacity: 15 to
150 pF.
Pickup coil: Space winding 5 (= 2 + 3) times of 26th enameled wire with a diameter of 0.45 mm on
both sides of the loop coil. The inductance of the primary coil measured with the LCR meter was
276 μH. When connecting this loop antenna to the hand-made L meter and measuring the oscillation
frequency, the calculated value was 2.958 MHz, but actually it fell to 1.898 MHz. From the
oscillation frequency difference stray capacitance was calculated to be 15 pF. As a result,
the tuning frequency range was 746-1750 kHz, and it turned out that it was close to feeling
actually used. Although the tuning frequency shifted slightly higher, NHK 1 and 2 are no
problem because they are very strongly intrinsically entered.
My own machine No. 3 was also made using cheap wood bought at the 100 yen shop. Coil No. 26
Copper wire, variable condenser of 25-220 pF for TS520. After completion we used the Sony’s
tuner (ST-S333ESG) where the reception condition has been greatly improved. Although this
tuner had the attached antenna, I connected the pickup coil directly to the antenna terminal
without using it. Circuit area: 33 cm × 33 cm, coil length: 4 cm, number of turns: 18 turns
of space winding, coil pitch: 2.4 mm, coil copper wire diameter: 0.45 mm, variable capacity:
25 to 220 pF, pickup coil: loop coil It is three times space winding of the 26th copper wire
with a diameter of 0.45 mm on the inside.
The inductance of the primary coil measured with the LCR meter was 216 μH. When connecting
this loop antenna to the hand-made L meter and measuring the oscillation frequency, the
calculated value was 3.344 MHz, but it actually decreased to 2.136 MHz. From the oscillation
frequency difference stray capacitance was calculated to be 15 pF. As a result, the tuning
frequency range was 707-1713 kHz, and it turned out that it was close to the feeling actually
used. NHK 1 and 2 which are out of the tuning range are originally very strongly entered,
so there is no problem.