diy, electronics, Radio, Videos September 15th, 2010
Foxhole radio receiver or Crystal receiver is a form of radio that does not operate on local oscillator, which makes it hard to be detected by other electronic device. One of the most interesting thing of Foxhole radio is that it could be operated without the use of batteries, as it is powered solely by the radio waves through its long wire antenna.
Foxhole radio was (supposedly) popular during World War II because it enabled the GI to receive radio broadcast in the middle of the war, particularly in France as the Germans has outlawed the use of radio by civilians, thus the American GI need to build their own receiver to receive broadcasts. Typical component of foxhole radio during those days are : a period razor blade (not the newer galvanized one), carbon (obtained from pencil) and some copper wire with woodblock or cardboard as its base.
I’ve found a video on Youtube on how to build a Foxhole receiver, it still requires considerable skills and experience to build a working version of the receiver though.
Here’s another 11 meter Moxon Antenna plan suitable for 27MHz CB, Freeband and lower 28MHz Amateur Radio operation band.
A- 392.09 cm (154 3/8 inch)
B- 58.62 cm (23 1/16 inch)
C- 11.25 cm (4 7/16 inch)
D- 73.4 cm (28 7/8 inch)
E- 143.27 cm (56 7/16)
Gain, Radiation Pattern (mounted at approx 30feet)
Gain : Approx 10-11dBi (30 feet above the ground)
Freq range : 27.300 MHz – 28.300 MHz
The main advantage of Moxon rectangle antenna are :
- Compact and Small
- Has considerable gain
- It can eliminate noise on HF band
- Easy to construct
- Suitable for HF operation (mid-low radiation angle)
Refer here for 10 meter Moxon Antenna Plan for Amateur Radio operation (28.2MHz-28.8MHz) : 10 Meter Band Compact directional antenna, Moxon
I think many of you might have heard about this particular 2 meter VHF antenna. Called
“Antenna ASTRA” which derived from the name of one of the most popular Amateur Radio Society in Malaysia.
Here is the details of its construction. Click on the photograph to enlarge it.
KakiBiawak @ Astra Antenna in action
Here are few photos that 9W2AZV and I have taken during the course of building our 6 element OWA yagi with 10dbi gain.
Materials used to contruct the antenna
- 8mm aluminium tube, 20 feet
- 6 feet length of 3/4″ PVC plumbing pipe
- Ordinary household plug box
We use a plan taken from LB Cebik (W4RNL) website, first covered in : 10dBi – 6 element OWA Yagi-Uda Antenna for 2 meter band
Here are the photos of the antenna in construction :
For starters… It does not actually sounds like that, I had to lower the voltage because the speaker output is too loud and you can hear that i’m not a good at sending morse too.
Still in progress, I’m still looking to modify it abit and put it in a nice box and attach it with a decent key.
This will be my next homebrew project, a morse practice oscillator circuit. 9W2AZV and I are going to build this as we are preparing ourselves to perfect our Morse code sending/receiving skills.
In the spirit of amateur radio/ham, we will homewbrew the equipment using easily obtainable parts from our nearest electronic stores.
Here’s the circuit
We are still thinking of the easiest and cheapest way to homebrew the keyer, but we are considering to use discarded/faulty computer mouse as our first keyer.
As a bonus, we thought of hooking this keyer straight to PC serial port, so we could use it with XChat CWirc plugin to enable us to test our Morse skill on the irc.
With the amount of work i’m having this week, I would estimate that this project would be completed by the end of March. So stay tune for photos!
Here is a guide to modify your PC power supply unit to power up your mobile rig. If its done correctly you can have a cheap (regulated) VDC power supply solution for your mobile rig to operate at home.
First get a ATX PC power supply from the nearest computer store. Price is around RM30-70.
Make sure it could supply sufficient current. Look at the label. We need at least 10-17amp at 12V for a sufficient operation of mobile rig. Lower Ampere rating means that your mobile rig cant transmit with a typical HiGH setting (50w).
Look for ATX power connector. It should look like this.
Look for black and green wire at the ATX connector. The wire position is 4th from the top left side of the connector and 4th from the bottom right side from the connector as pictured above.
Read the rest of this entry »
Slim Jim (J Integrated Match J-Pole) is probably the most easiest and powerful 2 meter antenna to build provided you have the exact measurement and material to build it.
This how to will show you how to build a 2 meter slim jim antenna from ordinary insulated copper wire commonly used for carrying AC (alternate current) electricity in your household.
Slim Jim construction basic
I am not only going show you the measurement of slim jim antenna for specific frequency, but I’m going to show you how to calculate slim jim antenna by your own using the basic formula below.
The figure above shows that the longest side of slim jim is 3/4 wavelength long and the shorter side of the slim jim consist of 1/2 wavelength and 1/4 wavelength long seperated by a gap.
The feedline (coax cable) is normally connected 1/20 wavelength from the bottom of the slim jim antenna with the center conductor connected to the longest side and the shield/braid is connected to the shorter side.
Building the Slim Jim antenna
This guide assume you want to build a slim jim antenna that centered on 146MHz.
The formula for calculating wavelength in metric system is 300/(freq MHz)
Using the formula from the figure, we have :
300/146 = 2.055 M
Wavelength = 205.5 cm
Wavelength x copper wire velocity factor = 205.5 cm x 0.94
= 193.17 cm
3/4 wavelength = 193.17 x 0.75
= 144.88 cm (57″)
1/2 wavelength = 193.17 x 0.5
= 96.585 cm (38″)
1/4 wavelength minus gap = 193.17 x 0.25 – 2.6 cm
= 45.69 cm (18″)
Coax tap = 193.17 x 1/20
= 9.6 cm (3 3/4″)
- 3/4″ diameter PVC (20mm) – 6 feet (180 cm)
- ordinary insulated copper wire for carrying altenate current (AC) – 11 feet (3.40 meter)
- Cable ties
- Soldering iron
- Glue gun
- Somthing to make a hole on PVC pipe
Wire Slim Jim Building Steps
- First take the PVC pile and measure it according to the 3/4 wavelength formula above (144.88 cm).
- Make two holes at the opposite side of the pipe. This hole is used for putting the copper wire through the pipe. Repeat this step 144.88 cm away from the top hole. Both of these holes will hold the copper wire.
- Insert the wire through the hole until both end reaches each other on one side of the PVC pipe. Then measure the length of the wire and cut the wire on that side so the setup resembles the figure above.
- Cut the wire insulation (but leave the wire uncut) 1/20 wavelength away (9.6 cm) from the bottom of the PVC pipe, again refer the figure above.
- Solder the center of the coax cable at the longest side of the slim jim (3/4 wavelength part) and the braid/shield at the shorted part of the antenna.
- Test the antenna using SWR meter to ensure that its SWR is at minimum or within acceptable level.
- There you go, you’ve build yourself your own 2 meter Omnidirectional Slim Jim antenna for less than USD2 (RM 6.00)
2 Meter Wire Slim Jim Antenna in action