Category Archives: General

Articles about Amateur Radio and the Nashua Area Radio Society. This is a general category which includes most articles on our website.

It’s All About The Decibels – Factors In Enhancing Station Effectiveness

Reposted By Layne AE1N

In electronics and communications, the decibel (abbreviated as dB) is a logarithmic expression of the ratio between two signal power, voltage, or current levels. In acoustics, the decibel is used as an absolute indicator of sound power per unit area. A decibel is one-tenth of a Bel, a seldom-used unit named for Alexander Graham Bell, inventor of the telephone.

Suppose a signal has a power of P1 watts, and a second signal has a power of P2watts. Then the power amplitude difference in decibels, symbolized SdBP, is:

SdBP = 10 log10 (P2 / P1)

This is much easier to understand by observing the table below.

1  dB ~ 30 percent increase

2 dB ~ 60 percent increase

3 dB ~ 100 percent increase

6 dB ~ 400 percent increase (~ 1 S-unit)

NOTE: For purposes of this article, our “Zero-Point” is a modern SSB transceiver running 100 watts to a half-wave dipole up about 30 feet. The objective is to improve station effectiveness in any various ways:

-27 dB ~ Switch from CW to AM

-17 dB ~ Switch from CW to SSB

-14 dB ~ Switch from CW to FM

-12 dB ~ To protect final transistor blow out manufacturers recommend reducing power to one-fourth normal when switching from ‘intermittent modes‘ (CW, SSB) to ‘Key-down’ modes (AM, RTTY, Digital).

– 4 dB ~ Switch from CW to RTTY.

+2 dB ~ Switching from FT8 to JT4. FT8 is operationally similar but four times faster (15-second T/R sequences) and less sensitive by a few dB. (On the HF bands, world-wide QSOs are possible with any of these modes using power levels of a few watts (or even milliwatts) and compromise antennas.

+2 dB ~ Switching from JT9 to JT9A. JT9A is 2 dB more sensitive than JT65 while using less than 10% of the bandwidth.

+2 dB ~ 2 Element collinear arrays.

+ 2 dB ~ single Cubical Quad loop.

+2.2 dB ~ 2 Element end-fire array 0.125 wave spacing.

+2.8 dB ~ 2 Element broadside array 0.64 wave spacing.

+ 3 dB ~ the ambient noise level has a profound effect on your ability to hear weaker signals. The following data was from VOACAP. VOACAP (Voice of America Coverage Analysis Program) is free professional HF propagation prediction software from NTIA/ITS, originally developed for Voice of America:: For 100 watts to a dipole at 33 feet located in grid square FN42 on a path to Central Europe at 1800 GMT. The following circuit probabilities are shown based on noise level at the receiver site: Quiet 55%; Rural 53%; Residential 42%; Industrial 26%; Noisy 23%. It appears that a noise quiet area has a 3 dB advantage.

+3 dB ~ 5/8 wave vertical vs. ¼ wave vertical hence the popularity of the 43 foot vertical.

+3 dB ~ Extended Double Zepp antenna.

+3 dB ~ Raise power from 100 to 200 watts.

+3 dB ~ vertical stacking of 2 identical antennas (0.5 to 0.75 wavelength spacing).

+3.4 dB ~ Moxon antenna.

+3.9 dB ~ 2-element Yagi parasitic director.

+4.3 dB ~ 13-32 MHz Log Periodic.

+4.5 dB ~ 4 element collinear array.

+6 dB ~ Raise power from 100 to 400 watts.

+6.6 dB ~ Rhombic 2 wavelengths per leg.

+6.8 dB ~ 4-element yagi beam.

+7 dB ~ Switch from CW to PSK31.

+7.3 dB ~ 2-element Cubical Quad.

+7.5 dB ~ 10 wavelength long wire at peak lobe.

+7.9 dB ~ 5-element yagi beam.

+8.5 dB ~ 6-element yagi beam..

+8.7 dB ~ 3-element Cubical Quad.

+9 dB ~ Raise power from 100 to 800 watts.

+10 dB ~ 3-element tribander.

+10 dB ~ Rhombic 4 wavelengths per leg.

+10.5 dB ~ 4-element Cubical Quad.

+11.1 dB ~ 11-element yagi beam.

+12 dB ~ Raise power from 100 to 1500 watts.

+13.4 dB ~ 19 element yagi beam.

+20 to 25 dB ~ switch from SSB to CW. It is mostly the signal-to-noise (S/N) improvement on the receive side that gives you the advantage on CW.  Assume a 2.5 KHz receive filter needed for SSB, and a 250Hz receive filter used for CW.  Now you have a 10dB advantage.  However, it is also easier to hear a CW tone than it is to understand SSB in a noisy environment.  I.e., the required S/N for CW copy is lower than for SSB copy. So, add a few more dB advantage to CW.  So, a rule of thumb is that CW has about a two S-unit (12dB) advantage or so over SSB. A 100-watt CW signal is equivalent to a full legal limit SSB signal. 20 to 25dB is a reasonable expectation for seasoned CW ops when the entire system includes the operator.

+25 dB ~ Switch from CW to FT8.

+25dB ~ Switch from CW to JT65.

 

 

These charts are from “How Much ‘Punch’ Can You Get from Different Modes?” by Kai KE4PT and Bruce N0ADL in QST, December 2013.

COMMENTS – Any change in power has no effect on receiver capabilities. Antenna gain figures are typical for that type of antenna. No cost/benefit attempt is made here. Most hams have limited pocketbooks. Besides marketplace prices are ever changing. And time is limited. Elevating you vertical slightly and installing 4 radials is a lot faster than laying down 120 radials!                                      73,  Layne AE1N

References:

http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-1.8.0-rc3.html

Students Analyze HAB-2’s Flight Data

The HAB team members in NARS have created a five-session curriculum to teach physics, atmospheric science, and radio technology that we use as part of our HAB launches. The last session is the most fun of all – analyzing the telemetry data from our HAB’s flight to see what the students can learn from it.

High-ALtitude Balloon Data Analysis
HAB-2 Flight Data Analysis

Our students at Bishop-Guertin High School that participated in our High-Altitude Balloon 2  launch this past weekend got together to analyze HAB-2’s flight data.  All of our students tracked HAB-2 using APRS.fi and were excited about the HAB’s flight and final altitude of almost 118,000 ft!

Flight Path

We began by reviewing our flight predictions and expectations for atmospheric conditions that we covered in our previous classroom sessions. You can see the materials that the students worked from via the preceding link. Also, the full set of data from HAB-2’s flight computer can be viewed as well.

HAB-2 Predicted Flight Path
HAB-2 Predicted Flight Path

We began by comparing the predicted flight path with the actual data from the APRS system on HAB-2.

HAB-2 Actual Flight Path
HAB-2 Actual Flight Path

The students concluded that the shape and direction of the predicted and actual paths matched quite well giving us confidence in the path modeling software.

Balloon Performance

Balloon Performance Calculator
Balloon Performance Calculator

They also noted the HAB-2’s ascent took longer and went much higher than the Balloon Calculator we had used predicted. After some thought, one of the students observed: “maybe we did not put enough helium in the balloon”.  This tuned out to be correct. We checked the scale that we used to set HAB-2’s lift with calibrated weights and we found an error in the scale’s calibration that led us to put about 200 g less lift (less Helium) in the balloon than our model required. We also used the same scale to weight the flight platform. These errors would certainly account for the higher altitude and long ascent times that we experienced.

Temperature and Pressure

High-Altitude Balloon Data Aalysis
GoPro Camera Early Shutoff vs. Temperature (click to enlarge)

The students also looked at the pressure and temperature data from the flight. The pressure was about what was expected but the students noticed that HAB-2 had flown through some temperatures as low as -70° F! The discussion turned to the question of why our video cameras had stopped recording at almost exactly the same time – 53 mins into the flight. An examination of our temperature data gave as a probable answer: the temperature took a dip to -50°F about the time that the GoPro video cameras shut off! Their LiPo batteries are only rated to about -40°F. We concluded that we’d need to find a way to keep the camera batteries warm during our next flight.

Other Questions

High-Altitude Balloon Data Analysis
High-Altitude Balloon Data Analysis Questions

The students discussed some additional questions and previewed some raw video from the flight and the recovery included a flight path simulation created by Wayne, AG1A.

HAB-2 Open House

Amatuer Radio Open House
Amateur Radio Open House

We are planning an open house for the students at our QTH to wrap up the project and to preview the final light video. Members of NARS are welcome to join us for the open house. You can find more information about it here.

I especially want to thank all of the NARS members who worked to prepare for and assist the students with HAB-2:

Without our HAB team, HAB-2 and the STEM learning experience that it provided would not have been possible. Thank you all for helping us to create a positive STEM learning experience through Amateur Radio.

Fred, AB1OC

Member Spotlight – Jamey, KC1ENX

I am very new to Amateur Radio and came into the hobby almost by accident. A few years ago I had been looking into better communication while out hiking after myself and Abby (AB1BY) were separated from the rest of our hiking party coming down Mount Washington.  We ended up coming down in the dark – with headlamps – and were okay, but we were frustrated that we could not let the rest of our party know we were oka but just slow.

I started searching the web trying to learn more about FRS/GMRS, CB radio and anything else that might work. During my search the Nashua Area Radio Club website came up and they had a licensing class coming up… the rest is history!

Speaking of history, let me tell you a little about myself that is non-ham related. I have worked as a tennis professional for the past 25 or so years. I am the current Director of Junior Development at the Longfellow Tennis & Health Club in Wayland, MA. We have one of the largest junior programs in the north east US and I truly love my job! I also work as a National Trainer for the United States Tennis Association (USTA) and travel to other clubs around the country to help educate other pros on the teachings of junior tennis.

KC1ENX, KC1FFX, and AB1BYI have two harmonics, Connor, KC1FFX and Abby, AB1BY. Both are licensed amateur radio operators. The three of us have not yet been able to convince my XYL, Gretchen, to get licensed… but, we keep trying!

KC1ENX, KC1FFX, and AB1BY

Outside of tennis and Ham Radio, I enjoy hiking, camping, kayaking (even when not rescuing HABs), canoeing and pretty much any other outdoor activities. I also have a love for motorcycling, but can no longer ride due to an inner ear disease which affects my balance. I have ridden in a few Iron Butt (Minute Man 1000) rides – think of a big, long distance scavenger hunt! One year I rode over 1300 miles in 24 hours. I loved riding and would ride rain or shine for many years. Both kids also enjoyed many adventures on the bike!

 

As far as my interests in Amateur Radio I have many. I could be diagnosed with Ham Radio ADD. There is just too much to learn and enjoy in the hobby! I really enjoy working mobile HF on my Icom 7100 and Tar Heel II antenna. I also enjoy contesting – especially on a good station like at Fred’s AB1OC and Anita’s AB1QB QTH. My favorite activity is portable operations. I have enjoyed Summits on the Air, Parks on the Air and sometimes just getting out with the kids and throwing up an antenna and operating. I am learning new things about this hobby every day.

As a new Ham, I am always curious to learn more about this great hobby and I consider myself very lucky for having found the Nashua Area Radio Society. I’m honestly not sure I would still be on the air if it weren’t for the all of the club’s activities and enthusiastic members.

Jamey, KC1ENX

Abby, AB1BY Interview on Ham Nation

One of our own, Abby AB1BY appeared on Ham Nation on Wednesday, October 25th. The show including Abby’s interview was streamed live over the Internet. Gordon West, WB6NOA, interviewed Abby. You can view Abby’s Interview (about 3:22 in from the beginning) below:

Abby was quite a hit during her Ham Nation debut. The chatroom activity associated with her segment was off the charts! Gordon has invited Abby back to do a monthly segment on Ham Nation. Stay tuned!

Fred, AB1OC