Antenna situation at JO20vx

Since 8-May-2020 I’m quite more often QRV from JO20vx, the city of Geleen in The Netherlands because of home care duties. One advantage of this location is that there is a 30m long garden that is about 7 meters wide, so there are plenty of opportunities to play with different antennas in a low noise environment. I can carry two sets of fiberglass mast elements with me while going here, and whatever fits in the car.

Setup 1: a mast in the center of the garden and a 20 and 40 m band antenna, getting everything 10 meter off the ground is a challenge

Setup 2: a smaller pole in the garden, few meters closer to the house, it is doable but the antennas at too low, will try it in the future with a delta loop.

IMG_0180
The idea is nice, but this secondary mast/pole is too low, the other mast elements are but to get above a tree right behind me.

Setup 3: tall pole at the end of the garden, and a g5rv to one of the chimneys on the house, benefit is that it somehow works

IMG_0197

IMG_0198
This is the better way to do it, a tall mast at the end where a metal gate is used as a support, and a G5RV to the roof
IMG_0199
From the second floor looking down on the garden

Typical setup, ft857d, travel tuner, 3 way coax switch so you can switch between the SDR, the radio and an antenna analyzer. The SDRplay rspduo is for band monitoring.

IMG_0200
Modifications: get ethernet cable upstairs and free this plank to work on.

Last update 18-May-2020

Counting is fun

Decimal, hex, octal, binary, Gray and BCD compared (left), including a rotary encoder setup (right)

counting_is_fun

Note the difference between counting in binary and in Gray code, the latter is used in rotary encoders and digital modulation. Try to understand rotary encoders and connect one to an Arduino, as you can read here

1:6 Balun, 50 to 300 Ohm

The design comes from F6GWO and it turns out to be useful for transforming a 300 Ohm symmetric transmission line to a 50 Ohm asymmetric coax cable. I made it with the available material in the shack, and measured the SWR when the symmetric side is terminated with a 300 Ohm resistor:

IMG_0144
How to make it
IMG_0157
Testing the reflection with a MetroVNA
balun6
Observed SWR against Frequency, so it is good enough, maybe the 80m band and frequencies beyond 30 MHz should be avoided, this may be due to the quality of the ferrite core.

In reality 300 Ohm antennas are typically folded dipoles and delta loops etc. This balun could be useful for a receiving antenna’s, don’t think it will be able to withstand a lot of power and I didn’t intend to test that.

Last update: 6-May-2020

Speaker wire dipole

I’m on travel, have a laptop and a sdrduo with me, but there is no antenna in this house. Ran to the local store and got 100 meter of loudspeaker cable, and it is really all you need to make an antenna to listen to shortwave.

Just make a dipole with arms as long as the garden allows, and use the loadspeaker cable as transmission line. It will work because the impedance of this cable is around 75 to 100 Ohm, there will be impedance differences but around 7 MHz you should have a match with two dipole arms of 10 m. Use anything that you can find to secure the T part of this construction (use rope, wire straps, tape, etc)

They sell this as 0,75 mm loudspeaker cable, cut off 20 meter, split it in two parts, adjust until it somewhere fits in the garden, and use the remaining speakercable as transmission line
Add some rope at both ends and let it run from the roof to a tree in the back of the garden, the wire shouldn’t touch anything, that would probably deteriorate reception quality
Connect the cable to the P and the N of the Hi-Z of the rspduo and there you go. The impedance of the Hi-Z port should be 1 K Ohm, at the moment this is not too important.

Noise levels at this place are fortunately pretty low, there is no need for anything fancy. The speaker cable dipole is good enough to listen to the HF which was the intention of this project.

Here I compare my reception against the University of Twente websdr. This project is not a bad deal, think it is even more sensitive than the websdr.

Last update: 3-May-2020

Top loaded vertical for 80m

gploading

The third design for a small 80 m antenna is a top loaded ground plane vertical. In this case you take a 40m ground plane with 4 ten meter radials and you add four top radials which you can partially use as guy-wires. As you can see, we have 150 kHz width if the SWR has to stay under 2, and a little less when the SWR has to stay under 1.5 as some solid state amplifiers without tuner require.

Could be a fun design for field days, I would use a remote antenna tuner at the base to feed this antenna. This design has a radiation pattern like that of a ground plane. It should not be used for NVIS activities but could instead be used for DX’ing.

GPLOADING_pattern

Here is the NEC file:

CM Ernst Schrama, vertical with a loading coil
CE
GW 1 20 0 0 0.1 0 0 10.00 0.0005
GW 2 20 0 -4.5 5.5 0 0 10 1e-3
GW 3 20 -4.5 0 5.5 0 0 10 1e-3
GW 4 20 -10 0 0.1 10 0 0.1 1e-3
GW 5 20 0 -10 0.1 0 10 0.1 1e-3
GW 6 20 0 4.5 5.5 0 0 10 1e-3
GW 7 20 4.5 0 5.5 0 0 10 1e-3
GE -1
GN 2 0 0 0 4 0.003
EK
EX 0 1 4 0 1 0 0
FR 0 0 0 0 3.7 0
EN

It could like this in a green field.

IMG_0082

Last update: 21-Apr-2020 10:48

Wide-band 80m antenna

ontwerp breedband 80m

This design does not fit in your garden probably, but it is a wide-banded 80m antenna that can be put up for a field day, you need 76,4 meter of wire, several 60cm spreaders a central mast of 12 meter, rope and a trafo/balun below the antenna. If the SWR has to stay under 2 then you have 350 kHz bandwidth, if it has to be under 1.5 it is a bit over 150 kHz, not splendid, but better than what we had, in the previous design.

It should work without a tuner if the trafo/balun properly transforms 300 Ohm to 50 Ohm. The 100 Ohm resistor helps to make it more wide-banded, not sure how much it will dissipate. This is the NEC file:

CM Ernst Schrama, 80m folded dipole
CE
GW 1 62 -16.238 -0.300 2.625 -0.300 -0.300 12.000 0.001
GW 2 3 -0.300 -0.300 12.000 0.300 -0.300 12.000 0.001
GW 3 62 0.300 -0.300 12.000 16.238 -0.300 2.625 0.001
GW 4 3 16.238 -0.300 2.625 16.238 0.300 2.625 0.001
GW 5 62 16.238 0.300 2.625 0.300 0.300 12.000 0.001
GW 6 3 0.300 0.300 12.000 -0.300 0.300 12.000 0.001
GW 7 62 -0.300 0.300 12.000 -16.238 0.300 2.625 0.001
GW 8 3 -16.238 0.300 2.625 -16.238 -0.300 2.625 0.001
GE -1
LD 0 2 2 2 100 0
GN 2 0 0 0 14 0.006
EK
EX 0 6 2 0 0 0 0 0
FR 0 0 0 0 3.7 0
EN

Last update: 20-April-2020 at 8:40AM

40/80 meter antenna for small gardens

4080mbdipole

I never went into the field with this one, there is not enough copper in the house to make the loading coils. It came out of 4NEC2 and the idea is to create an inverted V dipole that could be used for 40 and 80m only by inserting loading coils near the end of the 40m dipole arm.

Be warned that you need a tuner for the 80m band, because it is a narrow banded high Q antenna. If the SWR has to stay below 2 then the tuning range is probably 50 kHz, which is not a whole lot, I would not recommend it for solid state amplifiers, or at least be careful with the tuning. The other concern is the size and weight of the loading coils. On a  32mm PVC pipe you need something like 100 turns to get it to work. Tell me what you got if you decide to make it, want to verify it? Here is the NEC file:

CM Ernst Schrama, 40/80 meter dipole with a loading coils
CE
GW 1 2 -9.25 0 3.19 -8.26 0 4.18 0.001
GW 2 26 -8.26 0 4.18 -0.44 0 12.00 0.001
GW 3 1 -0.44 0 12.00 0.44 0 12.00 0.001
GW 4 26 0.44 0 12.00 8.26 0 4.18 0.001
GW 5 2 8.26 0 4.18 9.25 0 3.19 0.001
GE -1
LD 0 2 1 1 0 0.00012
LD 0 4 26 26 0 0.00012
GN 2 0 0 0 14 0.006
EK
EX 0 3 1 0 1 0 0
FR 0 0 0 0 3.7 0
EN

Last update 21-april-2020 at 11:00