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.

Featured, General

How to Calculate Battery Life

BATTERY LIFE CALCULATORTo calculate battery life, use the formula:
Battery life (amp hours) = Battery Capacity (amp-hours)
Current Draw (amps)
Battery life (amp hours) = 2.6 (amp-hours) / 0.135 (amps)

Given your battery’s capacity of 2.6 amp-hours and a current draw in the receive mode of 0.135 amps (135 mA), you can plug these values into the formula:

Battery Life (hours) = Battery Capacity /  Battery Draw

Battery Life (hours) = 2.6 Amp-Hours / 0.135 Amps

Battery Life (hours) =    2.6 /  0.135

Battery Life (hours) = 19.26

With a 135mA current draw in receive mode, your battery will last approximately 19.26 hours.

For Example:

Elecraft KX2 Current Draw in Transmit Mode
The KX2’s current consumption during transmission varies based on factors like output power, operating mode (CW, SSB, DIG), and connected accessories.
At 5 Watts Output Power (Typical QRP Operation):
• CW Mode: Draws around 0.8 to 1.0 amps. Considering a 25% duty cycle, the effective average current is approximately 0.20 to 0.25 amps.
• SSB Mode: Draws around 1.5 to 2.0 amps. With a 30% duty cycle, the average current falls between 0.50 to 0.70 amps.
• DIG Mode: Draws around 1.5 to 2.0 amps. Given a 65% duty cycle, the average current ranges from 0.98 to 1.3 amps.
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At 10 Watts Output Power (Higher Power Operation):
• CW Mode: Draws around 1.5 to 2.5 amps. With a 25% duty cycle, the average current is approximately 0.38 to 0.63 amps.
• SSB Mode: Draws around 2.5 to 3.5 amps. Considering a 30% duty cycle, this results in an average current of 0.75 to 1.05 amps.
• DIG Mode: Draws around 2.5 to 3.5 amps. Due to a 65% duty cycle, the average current is roughly 1.6 to 2.3 amps.
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Key Takeaways:
• Higher output power increases current draw proportionally.
• Digital modes (DIG) have the highest duty cycle, leading to greater average current consumption.
• CW and SSB modes, due to lower duty cycles, are more battery-efficient, especially at QRP levels.
Understanding these current draws and duty cycles can help you optimize battery life for portable operations.
DUTY CYCLES – CW vs SSB vs DIG
The duty cycle of a transmitter refers to the percentage of time it actively transmits RF energy during operation. This varies significantly depending on the mode of transmission—CW, SSB, or digital.
CW (Morse Code) Transmitters
For CW transmitters, the duty cycle during active transmission typically ranges from 10% to 30%. This is because Morse code involves alternating between brief periods of transmission (the dots and dashes) and silence (the spaces between characters and words).
For example, if you’re sending Morse code at a moderate speed of around 12 words per minute, with evenly spaced characters and words, the transmitter might be active for 1 to 3 seconds out of every 10 seconds. This results in an estimated duty cycle of roughly 10% to 30%.
However, this is only an approximation. The actual duty cycle can vary based on several factors:
• The specific Morse code being sent (longer dashes vs. shorter dots).
• The operator’s sending speed and technique.
• Pauses or breaks between transmissions.
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SSB (Single Sideband) Transmitters
For SSB voice transmissions, the duty cycle is generally higher than CW but still relatively low compared to modes like FM or AM. This is because SSB transmits only when there’s audio input—primarily during speech.
The duty cycle for SSB typically falls between 20% and 40% during active voice transmission. This means that while conversing, the transmitter is active for part of the time when the operator is speaking, interspersed with silent periods between words, sentences, or pauses in conversation.
Factors influencing the SSB duty cycle include:
• Speaking rate and style (fast talkers vs. slow, deliberate speakers).
• The frequency and length of pauses.
• The nature of the conversation (continuous speech vs. short exchanges).
For digital modes over SSB (like FT8), the duty cycle can be much higher because data signals are more continuous compared to the sporadic nature of human speech.
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Digital Mode Transmitters
Digital modes exhibit the widest range of duty cycles, depending on the specific mode and the data transmission pattern.
• High-Duty Cycle Modes: Modes like PSK31, FT8, and JT65 involve continuous data transmission in structured bursts, often with very minimal breaks. The duty cycle in these modes can approach 100%, meaning the transmitter is active almost the entire time during data exchange.
• Lower-Duty Cycle Modes: In contrast, modes like Packet Radio (AX.25) or APRS transmit data in discrete packets with intermittent breaks. The duty cycle in these cases is lower and varies based on:
o Packet size and frequency.
o Network activity and traffic load.
o Transmission settings and protocols.
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Summary
• CW: 10% to 30% (depends on sending speed and style).
• SSB: 20% to 40% (varies with speech patterns and pauses).
• Digital Modes: Varies widely—from near 100% (FT8, PSK31) to much lower (Packet Radio, APRS).
Understanding these duty cycles is crucial, especially when considering transmitter cooling, power output settings, and overall equipment longevity.

Antennas, DX, Featured, General, Station Equipment

Low-Band Receive Antenna Upgrades at AB1OC-AB1QB

Low Band Receive System - NCC-2

We have two low-band receive systems at our station:

These antenna systems use short active vertical antennas in various combinations to create directional receive antennas for the low bands (80m and 160m).

We recently upgraded our low-band receive antennas to use the latest electronics. The upgrades improved the performance of both antennas and enabled us to contact China on 80m. You can read more about the project here.

We did a guest spot on DXendineering’s weekly video broadcast about the project. You can view the video here.

Fred, AB1OC

General, Homebrewing, Station Equipment

A Broadcast Interference (BCI) Notch Filter for General Coverage Receivers

General coverage short-wave receivers may lack preselection against strong AM broadcast stations, and these broadcast stations may overload the receivers. SDR receivers, particularly the USB type[1], that plug into your computer are examples of this receiver type.

When I was designing my 10-band QRP transceiver, I wanted to incorporate an AM notch filter into the receiver for general coverage. In this mode of operation, the bandpass and lowpass filters are bypassed leaving the front end of the receiver wide open.

Since there are no FM broadcast transmitters nearby, I chose to include a notch filter for AM only because the receiver gain in my QRP transceiver from 88 to 108 MHz is greatly attenuated.

Rather than design and build a suitable notch filter, I looked for a suitable commercial off-the-shelf  (COTS) product that I could package into what I wanted.  The solution was the Nooelec Flamingo+ AM – High Attenuation Broadcast AM Bandstop (Notch) Filter[2].

My transceiver is based upon the N3FJZ software and hardware architecture [3], and Rick’s software architecture provides for general coverage whenever the receiver is tuned to other than one of the 10 designated ham bands. Thus, under these conditions, all of the filters in the transceiver are switched to bypass mode. I made use of this feature to incorporate the Nooelec Flamingo+ AM Notch filter in the bypass path.

Should I decide to incorporate an FM notch filter into the design in the future, the Nooelec Flamingo+ AM notch filter is easily disconnected from the printed circuit board carrier, and it may be replaced with a Nooelec Flamingo+ FM – High Attenuation Broadcast FM Bandstop Filter [4].

The schematic of what was built is shown in Figure 1. Optically coupled, 2-channel Arduino relays[5] are employed. When a bypass command is asserted in software, the receiver RF is routed around the bandpass and lowpass filters in the transceiver when it is in receive mode, only, i.e., the bypass does not function when the transceiver is in transmit mode.

Figure 1. Filter Bypass With BCI Notch Schematic. When the software command is asserted to place the transceiver in bypass mode, the relay modules will bypass the bandpass and lowpass filters in the receive path and insert the Nooelec Flamingo+ AM – High Attenuation Broadcast AM Bandstop (Notch) Filter. Since the AM BCI notch filter is connected to the PCB with right angle SMA connectors, it may be replaced by an FM BCI notch filter, as desired. Please click on the figure to enlarge it.

A printed circuit board, Figure 2, was designed as a carrier for the optically coupled relays and AM BCI notch filter. Pin headers are used for all connections to the 2-channel relay modules. Dupont[6] wires provide easy interconnects for power and logic inputs while pin headers are used for relay connections into and out of the printed circuit board. Dupont wires may be homebrewed with suitable component parts and a crimping tool, or they may be purchased at predetermined lengths.

Figure 2. As-Built AM BCI Bypass Printed Circuit Board. The AM notch filter may be replaced by an FM notch filter of similar form-factor by disconnecting the right-angle SMA connectors. Please click on the figure to enlarge it.

Finally, the response of the Nooelec Flamingo+ BCI Notch was measured on a spectrum analyzer with integral tracking generator. The result obtained is shown in Figure 3. The measured notch depth is close to 70 dB over most of the AM broadcast band. This result compares favorably with the plot provided by Nooelec[7] in Figure 4.

Figure 3. Measured Nooelec Flamingo+ AM BCI Notch Depth. The performance of the AM BCI Notch printed circuit board was measured on a spectrum analyzer with integral tracking generator. The notch depth is approaches 70 dB over most of the AM band. Please click on the figure to enlarge it.

Figure 4. Nooelec Data. The plot found in the Nooelec data sheet compares favorably  with the measured data of Figure 3. Reproduced with permission from Nooelec. Please click on the figure to enlarge it.

Anyone wishing to duplicate this printed circuit board may contact me for a Gerber file. I will not be offering any printed circuit boards.

References:

1. https://www.nooelec.com/store/sdr/sdr-bundles/hf-bundles.html

2. https://www.nooelec.com/store/sdr/sdr-addons/flamingo-plus-am.html

3. http://www.remmepark.com/circuit6040/MAX-SSB/MAX-SSB.html#110

4. https://www.nooelec.com/store/sdr/sdr-addons/flamingo-plus-fm.html

5.https://www.amazon.com/gp/product/B081MVCS8F/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

6. https://www.amazon.com/TOAPPNER-Multicolored-Breadboard-Arduino-Raspberry/dp/B089FZ79CS/ref=sr_1_2_sspa?crid=IB4C4C33XMM4&dib=eyJ2IjoiMSJ9.tjHxIQLJsk16_0YVtUGN6Tqnr8euWNsWVjpSaq5RQkYtxZ9Cezy7x5qOhagKvYtMzwlO3bKCBbaL1aW0gvt6neKoy9ihFziKKV1XaMgGsZAE8xRYaSTrpxQdRvB0pAUE20gJVd3C2KcNPIu-KcdICH9n984YMZgPEz0KU8pLTtGa-RcD9BD6ef2DqvC9xEyQTaj2b0LmfNg1lNr1V_BlptXMnJAI1jqwkYqPQCB5h5I.fVWAD3xtI6a-TS73_L9fQ9c26h3fo70muKyIhPmYqA4&dib_tag=se&keywords=dupont%2Bwires&qid=1732556600&sprefix=dupont%2Bwires%2Caps%2C99&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1

7. https://www.nooelec.com/store/sdr/sdr-addons/flamingo-plus-am.html. Op cit.

 

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