Tuesday, July 19, 2016

I have a question about the term ‘meter’ as it relates to the various labels used for amateur bands..

Q John asks, “I’ve just started studying for my Technician license and I have a question about the term ‘meter’ as it relates to the various labels used for amateur bands. Does the ‘meter’ of a given band correspond to the wavelength of the frequency of that band?”

Not necessarily. When you’re discussing Amateur Radio frequency bands, consider their metric labels in broad terms only. This will be easier to understand once you know the historical background. However, let’s start by defining a “meter” in terms of wavelength.

To convert wavelength to frequency, the speed of light is used, as it is also the speed of radio waves. In metric, this is 300 million meters per second. So the conversion formula is:
F(MHz) = 300/wavelength

wavelength = 300/F(MHz)

So, 6 meters is really 50 MHz; 2 meters is actually 150 MHz and 70 centimeters (0.7 meters) is 428 MHz. Notice that the frequency that corresponds to 2 meters is well above what hams consider to be “2 meters.”

While some folks would like to have the bands named more accurately (2 meters would be 2.1 meters, for example), tradition
runs deep in this hobby and the majority feel this tradition should be preserved.

In this day of computer-controlled rigs, it is easy to forget that radio technology was once crude indeed. Before the advent of vacuum tubes, there was no such thing as an amplifying oscillator with feedback to control it. Radio signals were generated via a spark gap.

Anyone who has listened to an AM broadcast radio when a thunderstorm is approaching knows that sparks generate wideband RF. The lightning discharges will create bursts of RF that cover the entire AM band. Thus it was in the early days of radio—transmissions were made by spark and the best one could do to limit the output bandwidth was to use an output filter made of a couple of inductors and capacitors along with a narrow-bandwidth antenna. This determined what “band” you were on and you could hear everyone else on the same band at the same time.

Yes, it was bedlam after a fashion, but the range you could work was quite short (a couple hundred miles was “DX”) and there were far fewer operators then. The label for a particular band was broadly interpreted because the signals themselves were broad—and that legacy remains today. That’s why we have a “20-meter band” at 14 MHz even though the true frequency equivalent of 20 meters is 15 MHz!

From QST June 2001

When a beam antenna such as a Yagi or quad produces ...

Q George, VE3LTU, asks, “When a beam antenna such as a Yagi or quad produces a major radiation lobe at, say, 35º, would the radiation angle be improved by tilting the boom 20º toward the Earth? Would the radiation angle with respect to the Earth now be 15º, resulting in improved DX performance?”

A The short answer is “no.” An array as you describe has its major lobe aimed directly along the boom (0º elevation) when it is in free space. When ground is considered, it increases the elevation of the lobe. Therefore, it is the relation of the antenna to ground (height)
that determines take-off angle.

We can look at it another way. The radiation pattern of an antenna is a summation of the radiation each of many antenna segments as they interact with each other and the ground below
the antenna.

We can visualize the result by imagining a mirror image of the antenna below the ground surface by a depth equal to the antenna’s height above the ground. Thus, as we tip the antenna boom downward, the imaginary boom tips upward to counter it—we achieve nothing.

From QST June 2001

I have two low pass filters. If I put them both in series ...

Q George, AD5CQ, asks, “I have two low pass filters. If I put them both in series with my transmission line, will I get more reduction of harmonics or would the input losses be excessive?”

A The answers are “yes” and “maybe” respectively.

The amount of loss would be double that of a single filter, but depending upon the filter design, it may be acceptable. I have seen filters with insertion losses as low as 0.25 dB and a 0.5-dB total loss would be quite acceptable to most folks. The best way to check is to put a power meter in line after the filter. A 1-dB loss is about 21 W out of 100.

If you don’t have an external power meter, you can check the difference in receive signal strength. Find a strong steady signal like WWV or W1AW and try switching the filters in and out of line to see how much the S-meter changes.

A 1-dB change would be just about noticeable in terms of meter movement (it’s about 1/6 of an S-unit by the old Collins standard—not that any modern rigs follow the standard, but it should be in the ballpark).

From QST June 2001

I am currently running a Yaesu FT-901 transceiver ...

Q John, N9QC, asks, “I am currently running a Yaesu FT-901 transceiver with a Cushcraft triband Yagi antenna. I’m considering adding a long-wire antenna for 80 and 160 meters and upgrading to a more modern transceiver. Do you think the automatic antenna tuners included with many of today’s rigs would work for both antennas?”

A Most of the auto tuners incorporated into new rigs have limited tuning ranges. They’ll only deal with SWRs up to about 3:1. That may be sufficient to extend your ability to use your tribander beyond its 2:1 SWR bandwidth on each band. Don’t count on the built-in tuner having enough range to handle the long-wire, though. You will need a separate, wide-range tuner to load your long-wire.

From QST June 2001

Sunday, July 17, 2016

Can you offer some tips on chasing radioteletype (RTTY) DX?

Q Can you offer some tips on chasing radioteletype

A Glad to! Like any other form of DXing, the quest for RTTY DX
demands patience and skill. When a DXpedition is on the air with RTTY from a rare DXCC entity, your signal will be in competition with thousands of other HF digital operators who want to work the station as badly as you do. Sometimes pure luck is the winning factor, but there are a couple of tricks you can use to tweak the odds in your favor.

Let’s say that you’re tuning through the HF digital subbands one day and you stumble across a screaming mass of RTTY signals. On your computer screen you see that everyone seems to be frantically calling a DX station. Oh, boy! It’s a pileup!

You can’t actually hear the DX station that has everyone so excited, but what the heck, you’ll activate your transceiver and throw your call sign into the fray, right? Wrong!

Never transmit even a microwatt of RF until you can copy the DX station. Tossing your call sign in blindly is pointless and will only add to the pandemonium. Instead, take a deep breath and wait. When the calls subside, can you see text from the DX station on your screen? If not, the station is probably too weak for you to work (don’t even bother), or he may be working “split.” More about that in a moment.

If you can copy the DX station, watch the exchange carefully.
Is he calling for certain stations only? In other words, is he sending instructions such as “North America only”? Calling in direct violation of the DX station’s instructions is a good way to get yourself blacklisted in his log. (No QSL card for you—ever!) Does he just want signal reports, or is he in the mood for brief chats? Most DX stations simply want “599” and possibly your location—period. Don’t give them more than they are asking for. (A DX RTTY station on a rare island doesn’t care what kind of weather you are experiencing at the moment.)

When DX RTTY pileups threaten to spin out of control, many DX operators will resort to working split. In this case, “split” means split frequency. The DX station will transmit on one frequency while listening for calls on another frequency (or range of frequencies).

A good DX operator will announce the fact that he is working split with almost every exchange. That’s why it is so important to listen to a pileup before you throw yourself into the middle. If you tune into a pileup and cannot hear the DX station, tune below the pileup and see if you copy him there. If his signal is strong enough, he shouldn’t be hard to find if he is working split. His signal will seem to be by itself, answering calls that you cannot hear. This is a major clue that a split operation is taking place.

Finally, don’t neglect the other modes if you’re hunting digital DX. An increasing number of DX stations are now using PSK31, so make sure you add that to your list of operating modes.

From QST June 2001

The material in an NPN transistor consists of a positive layer (the base) surrounded by two negative layers...

Q Ken, KE6ZWN, asks, “The material in an NPN transistor consists of a positive layer (the base) surrounded by two
negative layers (the emitter and collector). How do the manufacturers build transistors so that the current flows correctly
between layers while at the same time keeping them insulated
from each other?”

A See Figure 1. Transistors are made up of layers of material
that are “doped” with impurities so that they are either “P” type (positive charge) or “N” type (negative charge). Now, these charges aren’t quite like the ones in a battery— they exist in the form of an occasional extra electron or positive ion (an atom with an electron deficit) that are available as “current carriers.”

Where two different layers of material touch, an exchange of current carriers takes place and a neutral (or near neutral)
“depletion region” forms (an area where the net charge is depleted).
In a bipolar transistor, the base-emitter junction depletion region is fairly thin, whereas the region between the base and the collector is rather thick.

From QST June 2001

Wednesday, October 19, 2011

Over the past two years or so, I have received dozens of QSL cards from DX stations ...

Q Joe, WT7V, asks, “Over the past two years or so, I have received dozens of QSL cards from DX stations that I’ve never worked. In fact, many of these QSLs confirm contacts supposedly made when my rig was completely off the air for weeks at a time. Do you think someone could be bootlegging my call sign?”

A Bootlegging is always a possibility, but it is rare. If the
cards seem to arrive in spurts, there is a more likely explanation.

It is not at all unusual for a call to be consistently misrecorded in contests. For example, K0NS gets several cards per year intended for K0DI, a very active CW contest operator. If you sound out the suffixes of both call signs in Morse, you can understand how someone could blur the two together. Early this year, NT1A inquired about some cards that were apparently meant for our own Dave Patton, NT1N, here at Headquarters. In the heat of a contest, missing or transposing the individual letters is easy to do.

From QST June 2001