Blogs

More features for the repeater database

Jan
04

I've been spending a bit more time on the repeater database. It's evolved from a simple html table with data from various sources, to a full-blown database-driven system that supports user editing and has more features than you can shake a stick at. You might ask, "Are all these features necessary?" and the answer is no. I didn't do this to try and compete with some ham radio repeater websites. I just did it to learn about databases, and to have some fun, while getting a useful list of repeaters in the area. The database now has a google map for every repeater, as well as websites, and other information in every entry. It's probably overkill, but like I said, it was a learning experience.

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Ham Radio's Newest Band: 600 Meters

Jan
03

Many have long awaited the arrival of the newest band for ham radio. The 600 Meter band was recently allocated by the International Telecommunications Union (aka: ITU) to amateurs worldwide. However, US hams are still waiting for the FCC to domestically recognize and allow operation on this band. There is currently a "Notice of Proposed Rule Making" on the table which would allow US hams to transmit on the frequencies between 135.7-137.8 kHz. However, the FCC is currently waiting for comments regarding these new allocations, particularly comments from power companies who operate some protection equipment in this band. It is expected that the FCC will allocate these frequencies sometime later this year. Amateurs can submit comments to the FCC about this proposed rule, and are encouraged to do so.

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Selecting a power supply

Nov
12

Many modern ham radios operate on low voltage DC instead of high voltage AC. This is done for several reasons. First, most of the circuits inside these radios actually run on low voltage DC, so high voltage AC isn't needed. Second, running the radio on low voltage DC saves space inside the radio. This is because the radio can directly accept the low voltage DC it needs, and dosen't need an internal power supply to convert from high voltage AC to low voltage DC. Finally, the last advantage is that these radios can easily be installed in a car or run on a car battery.

So, this leads to the main point. What power supply do I need for my radio if it says it requires DC? The short answer is: Many different supply will be adequate. The two most important things to pay attention to are the following:
Does it produce the proper voltage?
Can it supply enough current?
Many DC power supplies on the market today provide 12 Volts DC (Actually 13.8 Volts is considered "nominal"). It is important to check the specifications and make sure that the output voltage on the supply is close to what your new radio calls for. A few volts difference is usually OK.

Next, check the maximum continuous current rating of the power supply. The power supply should provide at least the amount of current your radio needs plus 10%. The extra 10% is headroom to prevent your power supply from overheating. Most hams follow this extra 10% rule and some go even higher. Remember that you radio will not always need the max current that is listed on the radio's specs. This is usually the current drawn when the radio is transmitting on full power. The current the radio requires when it's recieving is typically much less.

So, in conclusion, you will need a power supply that matches the voltage of your radio, and can supply enough current to keep your radio running. Extra features like meters aren't absolutely necessary, but can be nice for troubleshooting problems, however, they cost more!

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Washington State Repeater Database

Aug
22

My latest project has been to develop and easy-to-use repeater database for the state of Washington. It is currently filled with repeaters from across the state on bands from 10 meters up to 900 Mhz. I'm in the process of verifiying all of this data which has been collected from various sources on the internet. Some of them are cited with a link, and some were not able to be confirmed. I need help doing this. If you'd like to lend some help by simply getting on the air and trying out the listed frequencies in you're area, let me know! I'll get you access to the database editor right away.

I'm considering launching a full website with publicly available and free-to-download repeater information. I've found several site on the internet that offer this information, but I feel like there not good enough for my taste. The database on this site is a kind of trial run. If the trial is successful I may launch a world-wide database in the next few months. That will depend on how many people offer to help verify the information because I want to have "known good" data in the database.

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How To Use an Antenna Tuner

Aug
03

Using a manual antenna tuner can be a dauting task for someone who has never used one before. Before we begin using the tuner let's take a moment to define what an antenna tuner is, and some of its most important parts.

Contrary to what it's name implies, an antenna tuner does not "tune" an antenna. In fact, it does not modify your antenna in any way. It simply serves as an impedance matching device, or impedance matching network. Allow me to use a metaphore. The gears on a bicycle serve to connect the pedals to the wheel so that the person riding the bicycle can turn the pedals at an efficient speed, which is somewhere between 70-100 rpm depending on the rider. If you did not have these gears you would have to turn the pedals very fast when riding down hill, and very slowly when riding up hill. This is not efficient. The gears simply allow you to pedal at an effiecient speed so that you can deliver maximum power to the wheel at all times. The antenna tuner serves a similar, albeit much more complicated purpose. Note that the gears on a bicycle do not change the way the back wheel works, they simply change how the wheel is connected to the pedals. The antenna tuner operates in the same way. It does not change the antenna. Rather, it modifies how the antenna is connected to the radio so that the radio can deliver maximum power to the antenna.

In almost every antenna tuner you will find capacitors and inductors. These capacitors and inductors can be wired in several configurations, but the most common is two capacitors and an inductor wired together in a "Pi" network. Take a moment to look inside your antenna tuner sometime and identify these components. See how they move when you turn the dials on the front of your tuner.

Now that you have an idea of the basic components inside your tuner, and the purpose a tuner serves, let's take a look at the steps required to tune an antenna.

First, begin by setting the capacitors to their highest setting. Next adjust the inductor until the background noise in your reciever peaks meaning you see a rise in the S-meter. If you are not able to produce a peak in the reciever try reducing the settings of the capacitors to 90% of their highest setting, then adjust the inductor. If you are still unable to produce a peak in the recieved signal, reduce the capacitors to 80%, then 70% etc.

When you have found a strong peak in the recieved signal, you are close to you're optimal tuning point. It should be noted that there are many tuning points which will produce a low SWR, but in order to maximize efficiency you'll need to minimize the inductor setting and maximize the capacitor settings.

Next, put your radio in CW, FM, or AM mode. Do not use SSB mode because no power will be produced unless you are talking into the microphone. Make sure the output power setting is set to it's lowest value. After making shure that you can legally transmit on the frequency you've selected, key the transmitter and observe the SWR on the tuner. Fine tune the two capacitors until a low SWR is obtained. Again, remember that there are many combinations of settings that will produce a low SWR, but combinations with low inductance and high capacitance will have higher effieciency and reduce losses in the tuner.

Once the SWR reads zero, and you are confident that the inductor is set to the lowest value that will produce an acceptable SWR, you are finished!

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