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.
The (*)555 Timer IC software has been use in countless of electronic project that requires the use of square wave (Astable). NE555 IC can act as a timer, delayed switch (Monostable), Schmitt trigger and simple memory switch. Here a a selection of Youtube videos that demonstrate the usefulness of 555 IC timer for electronic hobbyist.
The 555 Timer can help any electronic hobbyist and newcomer to build circuits with Astable or Monostable configuration. The application is very easy to use as the user only need to key in their desirable value of when the 555 timer should activates or deactivates; and the software does the calculation for the capacitors and resistors value.
The software is written by Andrew Clarkson, and you can download the software from http://clarkson-uk.com/555-timer/
Late this few weeks I’ve been hunting and finding Solar Panels which can be use to power up various items. Among the Solar Panel that I’ve found is listed below.
1. 14 volt panel – obtained from a hobby shop
2. 4.5 volt panel – scrapped from a damaged garden light
3. 2 volt panel – scrapped from some car accessories
Why would I need solar panel for?
Just to satisfy my hobby in electronics. The place where i’m staying (Alor Setar, Malaysia) always receives equal amount of sunshine, (near the equator), except for monsoon season of course. So I’m thinking that, it’s kinda shame if I let it waste.
Among of my plans would involve of hooking up one of these panels with a regular car battery and inverter to power up my backyard lamp and various electronic projects that depends on solar power. I’m looking for any good schematic to aiding me, not too complex, but good enough for a beginner.
I would appreciate any of your suggestions, btw.
Here’s a 12 Element UHF Yagi antenna that I designed for my friend, 9w2azv. He’s going to use that antenna for his client, that needs to hit a repeater 10 kilometers away from their location.
Here’s are the measurement for the antenna :
Polar Plot for the Antenna (E-Plane)
Polar Plot for the Antenna (H-Plane) at 2 Wavelength height
Here is the YagiMAX file : 10 Element Yagi 457MHz
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
Recent events surrounding blogging community has caught my attention, in which a blogger was arrested in Singapore due to his racist remarks on his blog.
This is not the first case someone being arrested for writing irresponsible things in their website or blog. We had our share of bloggers which has been slapped with court action against them due to their writings.
For years, internet become more than a medium to communicate free speech. However blatantly using the freedom of the internet is not what we should do. We all have to abide by a set of rules and code of ethics when we write, especially when we are addressing the public.
Making undesirable remarks, spreading lies and misinformation should be avoided at all cost because it has negative impact to the community, as innocent lives might be ruined by what we write.
Similarly, those who has a website (or a blog) should learn from the hobby of Amateur Radio, where hams are bound by a similar code of ethics practiced throught out the world.
A good ham avoid talking about topics that are argumentative as well as sensitive issues which might hurt people feelings, even when it is just a guideline, the code of ethics are maintained and is still there. The bloggers community should adapt such code of ethics so we could have a better blogosphere, as I believe it is better than to be force to take legal action against the relatively few unethical bloggers.
Here are some of the photos taken during Kota Setar Amateur Radio Club (Kelab Alor Setar) Family Day on 8 March 2008. Below are the repeater maintenance activity taken on top of Gunung Keriang Hill during that day.
Btw, the guy in the blue shirt maintaining the repeater is 9W2USF, Handle: Amiruddin.
Gunung Keriang Repeater Team
You can get the rest of the photos here – RGK Repeater Gunung Keriang Photos, all of the photos taken from 9W2DOT website
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.
Continue reading “How to turn PC Power Supply to power mobile rigs”
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
Due to the enourmous size of 3 element Yagi and the current working condition on 10/11 meter band, I decided to accept the advice of 9W2RZL and thinking of constructing a directional antenna right after I obtain the 11/10 meter rig (which is maybe around April).
Moxon antenna might suit my need as it is :
- has gain of around 5 dBi
- Compact and Light weight
- Easy to construct
- designed for 50 Ohm impedance
- Great F/B ratio, useful for blanking noise
Here is the plan for the 10 meter Moxon antenna, centered on 28.5 MHz frequency.
- A – 382.43 cm (150 1/2 inch)
- B – 57.13 cm (22 1/2 inch)
- C – 11.02 cm (4 3/8 inch)
- D – 71.06 cm (28 1/4 inch)
- E – 139.76 cm (55 inch)
These calculation are made for 12 gauge wire using L. B. Cebik Moxon Calculator tool. The Moxon on the above photo belong to Mark Rabel