Tag Archives: HF

Featured, General, Homebrewing, Station Equipment

RF Driver Amplifier Circuit With Receive Bypass

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This article discusses how a 3W commercial off-the-shelf (COTS) amplifier [1] may be used to drive a COTS 30W power amplifier [2] for use in a QRP transceiver transmitter. When homebrewing, it can be challenging to determine when to design and build something from scratch or when to assemble it from COTS parts. Several low-power amplifiers were considered for use as driver amplifiers, and the one selected is capable of a 1W (+30 dBm) output with only 0.032 mW (-15 dBm) input, resulting in a 45 dB gain at 10.12 MHz. This amplifier works over the entire HF spectrum. The 30W power amplifier was advertised for use as a linear amplifier that follows a low-power transceiver. It is provided with a receive bypass relay circuit so that the received signal will pass through the linear amplifier unimpeded. The 3W amplifier, however, does not have a receive bypass circuit. To use it in this application, a receive bypass path must be provided. That is the subject of this article.

Component Parts

The 3W amplifier selected for this application is shown in Figure 1. It consists of two Monolithic Microwave Integrated Circuits (MMICs) cascaded to produce the specified gain and power output. It was acquired from a seller on AliExpress [3] for less than $15. Upon arrival, the circuit board was removed from its heat sink. That is when it was discovered that no thermally conductive paste of any kind was applied to the interface. The ground tabs on the MMIC amplifiers were designed to dissipate heat. However, the only conduction path is through the via holes in the circuit board in proximity to the ground tabs. This is an ineffective conduction path to the ground plane on the rear side of the circuit board.

RF Driver Amplifier

Figure 1. A Commercial-Off-the-Shelf MMIC Driver Amplifier. This is a commercially available MMIC amplifier with an advertised output power of 3W. When operated with 12 to 15 VDC, the amplifier overheats. There was better luck once a layer of diamond thermal compound had been spread between the circuit board and the heatsink. Once reassembled onto its heat sink, the amplifier ran lukewarm at an operating voltage of +9 VDC with a power output of 1W (+30 dBm) when driven with 0.032 mW (-15 dBm). If the photo is studied closely, the grey thermal compound may be seen finding its way to the top of the PCB through the PCB via holes. Please click on the image to open in a new screen.

Once diamond thermal compound {4] had been applied to the back of the circuit board, the thermal paste began to fill the via holes thereby increasing the area of the conduction paths to the rear ground plane and to the heat sink beneath.

Next, operation was attempted at +13.8 VDC. While not hot enough to boil water, the heatsink became uncomfortably warm with the module dissipating more than 6W. Clearly, something didn’t seem quite right. These modules were specified for operation between +12 VDC and +15 VDC for the stated output power. The reliability of operation at this temperature was questionable.

If the heat sink area and volume is not increased, the simplest remedy is to reduce the operating voltage. Operation at +9 VDC was investigated with very good results. The RF power output of the module at 10.12 MHz is shown in Figure 2. The modulation sidebands are due to the bench switching power supply used. An output power of 1W (+30.11 dBm) was achieved for  0.032 mW (-15 dBm) input power, and the power dissipation dropped to 3W. One watt is more than enough power to drive the power amplifier to 10W (+40 dBm). When cooled by the fan in the transmitter, the MMIC driver amplifier will operate reliably.

Figure 2A

Figure 2B

Figure 2. Output Power of the 3W MMIC Driver Amplifier. At A, the spectrum analyzer photo is of the amplifier output power at 10.12 MHz. The modulation sidebands that originate with the switching power supply are visible. An output power of +0.11 dBm is observed. At B, since a 30 dB attenuator protects the spectrum analyzer input, the actual power achieved is 1W (+30.11 dBm) for -15 dBm input power. The gain at +9 VDC operating voltage is 45 dB. This is 10 dB higher than the specified gain, at least at 10.12 MHz. Please click on each image to open in new screens.

The 2-channel relay selected for this application is shown in Figure 3. These are commonly referred to as Arduino relays. Typically, they are operated from the TTL outputs of an Arduino after inversion. The relays may be operated with positive logic or negative logic by moving a small jumper. The relay inputs are optically isolated which greatly simplifies their use.

Figure 3. A 2-Channel Arduino Relay. These relays are optically coupled and can be controlled with positive and negative logic by moving the tan jumper that is visible in the photo. This module consists of two discrete, individually controllable single pole double throw (SPDT) relays. Please click on the image to open in a new screen.

Voltage regulation is provided by the LM317 adjustable voltage regulator [5]. The ripple output of the device is not of concern because it is being operated from a bench power supply. The voltage adjustment potentiometer has been bypassed; nonetheless, since the ripple voltage tends to increase with increasing adjust resistance.

A 2N7000 MOSFET is selectable at the logic input to the relay pair. If selected, it serves two purposes; a high impedance logic input for CMOS as well as a method for logic signal inversion, if desired, at the relay input.

Circuit Design

The circuit was designed on EasyEDA [6], a free, easy-to-use online design software package. As is usually the case, the Gerber files were transmitted to JLCPCB [7], a printed circuit fabrication house in Hong Kong. Turnaround time is typically 5 to 10 days depending upon the complexity of the circuit.

The circuit schematic diagram is shown in Figure 4. All of the key components of the previous section are shown on the schematic. Note that the receive path is through the normally closed contacts of the relays. Thus, no relay coil current is required during receive.

RF Driver Amplifier

Figure 4. Driver Amplifier Receive Bypass Schematic Diagram. The module has been designed around readily available COTS component parts. All parts are of the through-hole variety since there is little area to be gained through the use of SMT because the amplifier and relay are so large. Please click on the image to open in a new screen.

The jumpers for logic high input and logic low input operation are shown next to J1 and J3. Some of the connections to the relay are made with pin headers and Dupont ribbon wires. Power connections to the driver amplifier are made by connecting wires to screw terminal, J8.

Through-hole components are used in construction. Surface mount (SMT) parts would not reduce the area of the circuit board by much because the 2-channel relay board and 3W driver amplifier are relatively large, and the driver amplifier connects to the circuit board with right angle SMA adapters.

Two SMA connectors provide circuit I/O.  SMA connecter, RF4, provides the interface to the transceiver bandpass filters while SMA connector, RF1, provides the interface to the power amp.

The relay coil is operated with supply +13.8 VDC while the driver amplifier is operated with regulated +9 VDC.

The circuit board layout is shown in Figure 5. Places for the 2-channel relay with mounting holes and the driver amplifier with mounting holes are provided. The driver amplifier will be connected to the PCB with right angle SMA-male to SMA-male adapters.

Figure 5. Driver Amplifier Receive Bypass Circuit Board Layout. This is the silkscreen view of the assembly. The dimensions of the board are visible in the photo. Please click on the image to open in a new screen.

A 3-D rendering of the design is provided in Figure 6. Please note that some of the components are missing because 3-D models were not provided for the entire online library.

Figure 6. A 3-D Rendering of the Driver Amplifier Receive Bypass Circuit Board Layout. This 3-D virtual reality image was generated by EasyEDA. Some of the components are missing because 3-D images of the parts were not found in the library. Please click on the image to open in a new screen.

Conclusions

A design has been described that may be useful in conjunction with just about any RF amplifier for use in ham radio transceivers. The amplifier receiver bypass described in this paper will permit bi-directional operation as is required in one direction on transmit and the opposite direction on receive.

References

[1] https://www.aliexpress.us/w/wholesale-3W-shortwave-amplifier.html?g=y&SearchText=3W+shortwave+amplifier&sortType=price_asc

[2] https://www.aliexpress.us/w/wholesale-30W-shortwave-amplifier.html?spm=a2g0o.productlist.search.0

[3] 3W shortwave amplifier. Op. cit.

[4] https://www.amazon.com/JunPus-JP-DX2-Diamond-Thermal-Grease/dp/B0D7ZB43CF/ref=sr_1_1?crid=2Y1JXHD9J9MJZ&dib=eyJ2IjoiMSJ9.4cYW0erokqTHc7fpr9sWpA.vo3kXvGYCUoitzHMexiezvzYV0lb71EJvz3U3OOC614&dib_tag=se&keywords=JP-DX2-JunPus&qid=1761789390&sprefix=jp-dx2-junpus+%2Caps%2C85&sr=8-1

[5] https://www.ti.com/lit/ds/symlink/lm317.pdf

[6] https://easyeda.com/

[7] https://jlcpcb.com/

Disclaimers

This circuit design is provided for informational and educational purposes only and is supplied “as is” and without warranties of any kind, express, implied, or statutory. No representations or warranties are made regarding the accuracy, adequacy, completeness, legality, reliability, or usefulness of this information, either in isolation or in the aggregate. This circuit design may contain links to or information based on external sources or third-party content. Endorsement and responsibility for the accuracy or reliability of such third-party information or for the content of any linked websites are not taken.

Featured, Homebrewing

IF to Audio Baseband Converters for QRP SSB

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Introduction

Previously [1], an RF to IF Converter was described that precedes this module in a 10-Band QRP Single Sideband (SSB) transceiver.

The IF to Audio Baseband Converter modules described in this paper both serve to convert a 9 MHz Intermediate Frequency (IF) to baseband audio upon receive and from baseband audio to a 9 MHz IF upon transmit. Only one of these modules is required, and an explanation is provided for why two have been designed and built.

The discussion in this paper will be restricted to voice transmission and reception. Digital data transmission and reception on SSB will not be discussed.

Though used in the form of a trigonometric identity in one of the derivations; discussion of the Hilbert transform has been avoided.

Circuit Design

There are circuit commonalities and differences for both circuit boards designed for this application.

Module Commonalities

Please refer to the schematic diagrams in Figures 1 and 2 for this discussion. Both IF to Audio Baseband Converters employ Bridged-T Diplexers [2][3], pi-attenuators [4], and impedance matching transformers [5] on the BFO ports of their Mini-Circuits ADE-1 mixers [6]. Both employ audio diplexers [7] on their mixer IF ports. Both employ a low noise LM723 regulator [8] in a millivolt DC power supply to unbalance a Mini-Circuits ADE-1 mixer used as a balanced modulator for the purpose of reinjecting a carrier into the up-conversion path upon transmit. The carrier is used for antenna tuning. The command to unbalance the balanced modulator is asserted from the Control Panel by depressing the push-to-talk (PTT) button on the MIC or the PTT push-button on the Control Panel once the F1 button on the Control Panel has been pressed to display Tune on the 3.2” TFT display [9].  The Control Panel and TFT display will be described in another article.

One further commonality is the dual-function use of ADE-1 mixers in both module designs. Upon receive, they serve as product detectors for demodulation of the time-dependent audio message. Upon transmit, they serve as balanced modulators to mix the time dependent audio message with the IF carrier frequency for up-conversion. Descriptions of how product detectors and a balanced modulators work are provided in later sections.

Module Differences

Please refer to the schematic diagrams in Figures 1 and 2 for this discussion. The first IF to Audio Baseband Converter module incorporates a Wes Hayward, W7ZOI, fixed gain, bidirectional, termination insensitive amplifier (TIA) [10][11][12] for both transmit and receive paths, while the second incorporates the W7ZOI termination insensitive, closed-loop, IF AGC amplifier [13][14][15] in the receive path, and an open-loop, variable gain, W7ZOI termination insensitive amplifier (TIA) [16][17] in the transmit path. The variable gain amplifier has been implemented with an open-loop, AGC amplifier to which has been added an onboard gain adjustment trimpot. This trimpot is used during module tests. It is removed during transceiver integration and is replaced by a control panel potentiometer that sets the transmitter drive level.

Figure 1. The IF to Audio Baseband Converter Schematic Diagram. This module employs a fixed gain W7ZOI bidirectional, termination insensitive amplifier (TIA) for receive down-conversion from 9 MHz IF to audio baseband and from audio baseband to 9 MHz IF for transmit up-conversion. A low-noise LM723 voltage regulator is part of a millivolt, DC, onboard power supply. Its purpose is to unbalance the ADE-1 balanced modulator so that a carrier may be injected during transmit for antenna tuning.

Figure 2. The IF to Audio Baseband Converter with Receive AGC Schematic Diagram. This module employs a W7ZOI Termination Insensitive Amplifier (TIA) with closed loop AGC for receive down-conversion from 9 MHz IF to audio baseband. A W7ZOI Termination Insensitive Amplifier (TIA) with open loop AGC is used for transmit up-conversion. A low-noise LM723 voltage regulator is part of a millivolt, DC, onboard power supply. Its purpose is to unbalance the ADE-1 balanced modulator so that a carrier may be injected during transmit for antenna tuning.

What is a Balanced Modulator?

In the time domain a SSB signal containing the message is generated by multiplying a time dependent audio message signal by a time dependent IF carrier signal in a mixer used as what is called a balanced modulator. The audio message information is injected into the IF port of the balanced modulator while a local oscillator (LO) signal is injected into the LO port of the balanced modulator. What results is a double sideband suppressed carrier signal in the time domain. There are other methods used to produce SSB signals, but we will limit this discussion to the use of a double balanced mixer for this example. The problem could also be described in the frequency domain, but that solution will not be presented at this time. For sake of example, we neglect higher order, odd harmonics of the LO signal because the LO signal is a square wave. Also, for simplicity, we will neglect the phase terms that accompany each of the signals.

In order to achieve the best possible carrier cancellation in a double balanced mixer used as a balanced modulator, care must be taken to ensure that all of the mixer ports have been terminated in 50-ohms. It is also essential to drive the mixer at its required signal level. Once these requirements have been implemented in the design, the signal leaving the balanced modulator will consist of two sidebands, an upper one and a lower one. The carrier will have been greatly suppressed.

The time dependent, equation for the output of a balanced modulator may be derived from two expressions; the first,

is the time-dependent audio message information that is injected into the IF port of the balanced modulator,

where:

It is important to remember that the time-dependent audio message signal may or may not be a single sinusoidal frequency. For example, voice is quite complex and contains many frequency components. For simplicity here, though, it is defined as a single frequency.

while the second,

is the time-dependent IF carrier signal that is injected into the LO port of the balanced modulator,

where:

For this discussion the assumption is made that the IF carrier signal frequency is much greater than the audio message signal frequency. Multiplying the audio message with the IF carrier, we have for the double sideband suppressed carrier (DSB-SC),

Substituting, we have,

We may recall from trigonometry that the product of two cosines is just,

Substituting, we have,

This equation is comprised of two terms, where the first term,

is called the upper sideband because the output frequency is higher than the carrier.

We know from trigonometry that,

Thus, for the upper sideband, we have,

where the minus sign is correct and is the result of trigonometry.

The second of the two terms is,

which is called the lower sideband because the output frequency is lower than the carrier.

We know from trigonometry that,

Thus, for the lower sideband, we have,

where the plus sign is correct and is the result of trigonometry.

These two sideband equations may be combined in compact form as the double sideband suppressed carrier (DSB-SC) signal,

where the minus sign represents the upper sideband, and the plus sign represents the lower sideband, however counterintuitive it may seem.

One might ask how one of the two sidebands is selected for transmission? The answer comes in the form of a very narrow (of the order of 2.6 kHz wide) crystal bandpass filter [10] centered somewhere near 9 MHz. If upper sideband transmission is desired, that frequency is shifted downward so that the upper sideband sits in the passband of the crystal bandpass filter. If lower sideband transmission is desired, that frequency is shifted upward so that the lower sideband sits in the passband of the crystal bandpass filter. This is accomplished by shifting the LO frequency to the balanced modulator by a few kHz.

All of this requires some a priori knowledge of where the center frequency of the crystal bandpass filter is located. Once known, the audio message information may be shifted so that it is centered in the crystal bandpass filter passband for either sideband.

What is a Product Detector?

In this context a product detector is a demodulator used to recover audio message information from a SSB voice message signal. If a double balanced mixer is used as a product detector, a SSB signal enters the RF port of the mixer while a local oscillator beat frequency oscillator (BFO) signal is injected into the local oscillator (LO) port. When the listener tunes the receiver BFO frequency close to the carrier frequency that was removed prior to SSB transmission, the audio message information becomes intelligible to the listener. This presupposes that the signal is transmitted on upper or lower sideband in accordance with conventions used on the ham bands. It is important that hams work to the same conventions everywhere on the planet or the system will break down.

Product detection may also be described in a few trigonometric equations. This time we use the same double balanced mixer as a product detector. After passing through our crystal bandpass filter, the upper or lower sideband signal is sent to the RF input of the product detector. A BFO signal is injected into the product detector LO port to match the frequency of the carrier that originally generated the SSB transmission. Once tuned to the correct sideband, the output of the product detector passes through a lowpass filter to remove all of the remaining high frequency components, thereby recovering the message audio.

In the previous section it was shown that the DSB-SC signal may be represented by,

This expression contains the message on both of the sidebands, where the carrier has been suppressed.

If we want to recover the voice audio message information, we select the appropriate sideband that has been transmitted based upon the ham band in use.

In order to simplify the expression appearing above without any discussion of the Hilbert transform, let’s make some simple trig substitutions, and we will dispense with any of the constant terms out front. Let’s represent the time-dependent voice audio message in this way,

Furthermore, we can use a trigonometric identity,

Transformations of this type are quite common in communication theory, but we will not dwell upon them.

These two quantities having been defined; we may write our equation for DSB-SC in this way,

Now, suppose that we multiply the preceding expression by the same carrier frequency, presumably in the product detector, and we have for the carrier,

where c(t) is the BFO carrier signal that matches the one suppressed during message transmission.

Then, having performed this operation; we will have recovered the modulating time-dependent voice audio message, where,

and where R(t) represents the recovered, time-dependent message prior to filtering.

Multiplying through, we have,

Again, invoking trigonometric substitutions,

and,

which yield,

This may be rewritten to show the carrier frequency instead of the angular frequency,

The first term contains the time dependent audio message information while the last two terms contain the carrier frequency. The carrier frequency terms may be removed by lowpass filtering after the product detector with an audio diplexer to recover the time-dependent audio message.

Why Two IF to Audio Baseband Converters?

The reason that two discrete IF to Audio Baseband Converters were designed and built is twofold.

First, I wanted to fast-track the SSB radio integration task if trouble was encountered with the IF AGC circuit. This turned out to be fortuitous, and that is exactly what occurred. It took some time to de-bug the circuit.

Second, I wanted to be able to compare receiver performance with, and without, IF AGC. Differences in receiver dynamic range and sensitivity were anticipated.

Construction

Both circuit cards were designed on EasyEDA [18] CAD software that is available for free download and use. PCB fabrication was completed from transmitted Gerber files by JLCPCB [19] in Hong Kong. Turnaround time was 10-days. In order to reduce the number of via holes on the circuit boards, 4-layers were adopted. The top layer consists of ground plane. Vertical SMA RF connectors on the surface of the boards put the ground plane to good use. DC and signal connections to the amplifiers and mixers are made via pin headers and DuPont wires as are visible in Figures 3 and 4. Each of the modules derives its input from a crystal bandpass filter [20] that has sharp skirt selectivity.

Several features are visible on each of the circuit boards:

·        W7ZOI Termination Insensitive Amplifiers (TIAs) in use on both boards to present 50-ohms to the balanced modulator RF port on transmit and the product detector RF port on receive

·        A Mini-Circuits ADE-1 mixer functions as a balanced modulator upon transmit and a product detector upon receive

·        A transformer on the BFO port to transform the impedance level of the SI5351 Clock Generator to 50-ohms

·        A pi-attenuator to adjust the BFO drive level to that required by the mixer

·        An LO diplexer is used to present 50-ohms to the mixer LO port

·        An audio diplexer is used on the mixer IF port to present a 50-ohm load to the IF port, and to filter out any RF appearing on the IF port upon receive so that the audio message may be recovered

·        A low noise LM723 voltage regulator is used in a millivolt power supply configuration so that the balanced modulator may be unbalanced for carrier injection

Figure 3. IF to Audio Baseband Converter without AGC. The IF to Audio Baseband Converter module without AGC consists of a W7ZOI bidirectional, termination insensitive amplifier (TIA) to the left, a Mini-Circuits ADE-1, +7 dBm level mixer at the center, and a millivolt power supply to the right. The mixer serves as a product detector for receive and a balanced modulator for transmit. The relay at the lower right switches 100 mV onto a 50 ohm termination at the IF port of the mixer to unbalance it. This serves to inject a carrier into the transmit path so that the antenna may be tuned to resonance. An audio diplexer is visible on the IF port. This serves to terminate the IF port in 50 ohms while providing a lowpass filter to pass the receiver audio. There is a transformer visible on the LO port of the mixer that serves to match the 76 ohm output impedance of the SI5351 clock generator used as the beat frequency oscillator (BFO) to the 50 ohms required by the LO diplexer and the ADE-1 mixer LO port. A pi-attenuator is provided between the transformer and the diplexer to drop the SI5351 level to +7 dBm.

Figure 4. IF to Audio Baseband Converter with AGC. A W7ZOI termination insensitive amplifier (TIA) is visible to the left. It is used during receive only, and it operates with closed loop AGC. The AGC output voltage also serves as the S-meter signal that is routed to the Arduino S-meter input for display on a 3.2” TFT display. Another W7ZOI termination insensitive amplifier (TIA), set to fixed gain for test, is visible second from the left. It is constructed from an amplifier that has an open loop AGC input. A potentiometer on the AGC port is used to set a fixed transmitter drive level. The Mini-Circuits ADE-1 mixer, second from the right is used as a product detector on receive and a balanced modulator on transmit. The circuitry to the far right generates 100 mV that is applied to the 50 ohm termination on the IF port of the mixer. This serves to inject a carrier into the transmit chain so that the antenna may be tuned to resonance.  The relay in the photo switches the 100 mV onto the 50 ohm termination on the IF port of the mixer. A transformer is visible on the LO port that transforms the 76 ohm output impedance of the SI5351 clock generator to the 50-ohms required on the mixer LO port. A pi-attenuator is located between the transformer and the LO diplexer to lower the signal level to that required by the +7 dBm mixer. An audio diplexer and lowpass filter provides a 50 ohm match to the IF port while allowing only audio to pass.

References

[1] Blustine, Martin, K1FQL, An RF to IF Converter for QRP SSB Transceiver Use, N1FD, 4 August 2025. https://www.n1fd.org/2025/08/04/transverter/

[2] Ibid.

[3] https://www.changpuak.ch/electronics/calc_16a.php

[4] https://leleivre.com/rf_pipad.html

[5] Blustine, Martin, K1FQL, Impedance Matching to an 8-Pole Quasi-Equiripple (QER) Crystal Bandpass Filter, N1FD, 21 May 2024. https://www.n1fd.org/2024/05/21/crystal-filter/

[6] Mini-Circuits, https://www.minicircuits.com/WebStore/dashboard.html?model=ADE-1

[7] Lewallen, Roy, W7EL, An Optimized QRP Transceiver for 7 MHz, ARRL, https://www.arrl.org/files/file/Technology/tis/info/pdf/93hb3037.pdf

[8] Texas Instruments, https://www.ti.com/lit/ds/symlink/lm723.pdf

[9] Adafruit, https://www.adafruit.com/product/1743?srsltid=AfmBOopGfznYc8RKuumddbQzWwXY_d1ByQd07CqiPAZ_xqBDg2jOWuzv

[10] Hayward, Wes, W7ZOI and Kopski, Bob, K3NHI, A Termination Insensitive Amplifier for Bidirectional Transceivers, 26 June 2009. https://w7zoi.net/bidirectional_matched_amplifier.pdf

[11] Land Boards, A Termination Insensitive Amplifier for Bidirectional Transceivers. https://land-boards.com/blwiki/index.php?title=A_Termination_Insensitive_Amplifier_for_Bidirectional_Transceivers

[12] Tindie, A Termination Insensitive Amplifier for Bidirectional Transceivers. https://www.tindie.com/products/land_boards/termination-insensitive-rf-amplifier/

[13] Hayward, Wes, W7ZOI and Damm, Jeff, WA7MLH, The Hybrid Cascode – A General Purpose AGC IF Amplifier, QST, December 2007. https://www.ka7exm.net/hycas/hycas_200712_qst.pdf

[14] Hayward, Wes, W7ZOI, Regarding Circuit Boards for the Hybrid Cascode General Purpose IF AGC Amplifier. https://w7zoi.net/hycas-pcb.html

[15] Carney, Todd, K7TFC, Mostly DIY RF, https://mostlydiyrf.com/hycas/

[16] Hayward, Wes, W7ZOI, Adding AGC to a Termination Insensitive Amplifier, 27 October 2021. https://w7zoi.net/tia+agc.pdf

[17] Carney, Todd, Mostly DIY RF, TIA-AGC RF Amplifier. https://mostlydiyrf.com/tia-agc/

[18] EasyEDA. https://easyeda.com/

[19] JLCPCB. https://jlcpcb.com/?from=VGBNA&utm_source=google&utm_medium=cpc&utm_campaign=13059631621&utm_content=581194145188&utm_term=b_jlcpcb&adgroupid=118955305341&utm_network=g_&gad_source=1&gad_campaignid=13059631621&gclid=EAIaIQobChMIssG71-mZjwMVBjIIBR1NEDo_EAAYASAAEgKrzvD_BwE

[20] Blustine, Martin, K1FQL, Impedance Matching to an 8-Pole Quasi-Equiripple (QER) Crystal Bandpass Filter. Op. cit. https://www.n1fd.org/2024/05/21/crystal-filter/

Disclaimers:

The circuits included on these PCBs were sourced from a number of authors. This is a somewhat advanced and expensive project, and some prior design and construction experience is recommended before taking on a project of this magnitude. These circuit designs are provided for informational and educational purposes only and are supplied “as is” and without warranties of any kind, express, implied, or statutory. No representations or warranties are made regarding the accuracy, adequacy, completeness, legality, reliability, or usefulness of this information, either in isolation or in the aggregate. These circuit designs may contain links to or information based on external sources or third-party content. Endorsement and responsibility for the accuracy or reliability of such third-party information or for the content of any linked websites are not taken.

Featured, General

When did WWV Move to Colorado?

During our weekly Sunday night VHF net, a question arose about the National Institute of Standards and Technology’s (NIST) time and frequency station, WWV. Net Control asked, “When did WWV move to Colorado?” While a few of us could answer, it became clear that many of the newer hams didn’t know much about the WWV station.

Myself, being a ham from Boulder, Colorado and now living in Nashua, New Hampshire, I saw this as a great opportunity to share information I’ve gathered over the years, both about WWV’s operations in Fort Collins, Colorado, and its move from Maryland in 1966.

WWV Site - Fort Collins, CO
WWV Site – Fort Collins, CO

WWV is considered one of the oldest continuously operating radio stations in the United States. It was first established in 1919 by the National Bureau of Standards (now NIST) and originally broadcasted from Washington, D.C. Its primary purpose has always been to transmit accurate time and frequency signals, which it continues to do today from its Fort Collins, Colorado facility. WWV’s long history of broadcasting time signals makes it a significant part of radio history in the U.S.

Boulder, Colorado, is home to the NIST (formerly the National Bureau of Standards, or NBS) Atomic Clock, which serves as the time and frequency standard for the United States and many other countries around the world. I’ve had the opportunity to view the Atomic Clock “in person” at the NIST Laboratory.

The NIST atomic clocks use cesium atoms to keep incredibly precise time. Here’s a simplified explanation of the process:

  1. Cesium Atoms: The atomic clock relies on the natural oscillation of cesium atoms. Cesium atoms absorb and release energy at a very consistent frequency when they transition between two energy levels.
  2. Microwave Frequency: The clock generates microwaves that are tuned to match the exact frequency of the cesium atoms’ oscillation. The frequency at which cesium atoms oscillate is exactly 9,192,631,770 cycles per second.
  3. Tuning to Maximize Accuracy: The atomic clock continuously adjusts the microwave frequency to ensure it matches the cesium atom’s resonance as precisely as possible.
  4. Counting Seconds: By counting these highly accurate oscillations, the clock measures time. One second is defined as exactly 9,192,631,770 oscillations of the cesium atom.
  5. Disseminating the Time: NIST broadcasts the official time using radio signals (via stations like WWV), the internet (through NIST’s network time protocol, or NTP), and satellite systems. These signals help synchronize clocks around the world.

NIST’s time standard is crucial for GPS systems, telecommunications, scientific research, and other industries that require precise timekeeping.

In 2013, when I was serving as the ARRL Colorado Section Manager, we hosted the Rocky Mountain Division Convention (Hamcon Colorado) in Estes Park, Colorado. Given its proximity to the WWV radio complex in Fort Collins, our committee thought it would be a great opportunity to arrange a tour for interested hams. Since WWV is a secure government facility, we needed special permission. The WWV Chief Engineer, who was also a ham, informed us that they had never conducted a tour before and it might be impossible, but he would ask. To our surprise, permission was granted with some necessary security measures in place. Interest in the tour was high, and we chartered a school bus to take a large group of hams to the facility.

10 KW - 5 MHz WWV transmitter
10 KW – 5 MHz WWV transmitter

The engineers at WWV went above and beyond, providing a comprehensive tour of the facility that included fascinating historical devices. We were able to visit the antenna sites and transmitters, with detailed explanations of their operations.

Historically, amateur radio operators played a key role in the technical development of the atomic clock and the WWV radio stations from their earliest days. Given that the atomic clock is housed in Boulder, CO, many members of the Boulder Amateur Radio Club (BARC) were among those who contributed to its development and advised on the WWV operations over the years.

Yardley Beers, W0JF
Yardley Beers, W0JF

ne of the more notable BARC members was Yardley Beers, WØJF (formerly WØEXS and W3 AWH), who earned his MS in Nuclear Physics in 1937 and a Ph.D. in 1941 from Princeton University, where Einstein was in residence at the time. Beers was a pioneering scientist who first utilized cesium as the core of the aforementioned time standard oscillator. He was a dear friend whose boundless curiosity, humor, and deep expertise in all things radio-related made him a wealth of knowledge for our club.

At 0000 GMT on December 1, 1966, the veteran time and frequency station WWV in Greenbelt, Maryland, shut down permanently. Almost simultaneously, a new station with the same call letters and services began broadcasting from Fort Collins, Colorado. The decision to construct the new station and relocate was driven by several factors, primarily the obsolescence of the old facility and significant maintenance challenges.

WWV 15-meter antennas
WWV 15-meter antennas

 

In contrast, the new station utilizes the latest transmitter designs, offering significantly more efficient operation. The setup also provides greater flexibility, as the transmitters consist of identical units—except for some higher-powered transmitters, which include an additional amplifier stage—that can be tuned to any frequency. At the old station, only a few of the eight transmitters were identical. Unlike the old transmitters, the new ones apply modulation at low levels, with all subsequent stages maintaining precise linearity. This allows for a wide range of modulation options, including AM or single sideband, with either sideband and any desired degree of carrier suppression. These features mirror those found in modern amateur radio transmitters.

Lastly, the move brings the benefit of administrative efficiency. WWV is now co-located with two other NBS standard frequency and time stations, WWVB (60 kHz) and WWVL (20 kHz), at the same site. Additionally, it is more convenient to synchronize the station with the NIST atomic standards, which are based in nearby Boulder, Colorado.

WWVH began operation on November 22, 1948, at Kihei on the island of Maui, in the then

territory of Hawaii (Hawaii was not granted statehood until 1959). The original station

broadcasts a low-power signal on 5, 10, and 15 MHz. As it does today, the program schedule

of WWVH closely follows the format of WWV. However, voice announcements of time

weren’t added to the WWVH broadcast until July 1964. In July 1971, the station moved to its current location, a 30-acre (12-hectare) site near Kekaha on the Island of Kauai, Hawaii.

Today, the methods for calibrating frequency, synchronizing time, and assessing propagation have evolved significantly due to advances in technology, though some traditional methods (like using WWV) are still in use. Here’s a comparison of how these tasks were done in the past versus how they are typically done today:

1. Frequency Calibration

Before (Using WWV and Manual Tools):

  • WWV Broadcast: Operators tuned their radios to the exact frequencies broadcast by WWV (e.g., 5, 10, or 15 MHz) to verify or adjust their frequency dials
  • .Signal Comparison: Operators might use frequency counters or calibrate their equipment using signal generators. By manually adjusting their radio to match the WWV signal, they ensured their equipment was tuned correctly.
  • Crystal Oscillators: Some radios used quartz crystal oscillators that needed periodic manual adjustments to maintain frequency stability.

Today (Using GPS, Software, and SDRs):

  • GPS Disciplined Oscillators (GPSDO): Modern radio equipment can be calibrated with GPS, which provides ultra-precise time and frequency data directly from satellites. GPSDOs lock the radio’s oscillator to the exact frequency provided by GPS signals.
  • Software-Defined Radios (SDRs): SDRs can automatically lock to known reference frequencies or signals, often bypassing the need for manual calibration.
  • Digital Frequency Counters: High-precision digital frequency counters, often built into modern equipment, can accurately verify a station’s frequency without the need for an external signal like WWV.

2. Time Synchronization

Before (Using WWV or Manual Clocks):

  • WWV Time Signals: Operators would listen to WWV’s hourly time announcements and manually synchronize their clocks to the audio ticks or the minute mark. This ensured they had the correct Coordinated Universal Time (UTC) for logging contacts.
  • Mechanical or Quartz Clocks: Station clocks were either mechanical or quartz-based, requiring manual adjustments for drift.

Today (Using NTP and GPS):

  • Network Time Protocol (NTP): Computers, logging software, and transceivers are often synced to the Internet time servers using NTP, which automatically keeps time to within milliseconds of UTC. Many hams now use computers with built-in NTP syncing for contest logging and communication accuracy.
  • GPS Time: GPS provides highly accurate time synchronization. Many modern radios or station computers are connected to GPS receivers that provide time directly to within a fraction of a second of UTC.
  • Atomic Clocks: Although not widespread in amateur radio, some operators use atomic clock-based devices for extreme precision in timekeeping, often integrated with GPS.

3. Propagation Monitoring

Before (Using WWV and Beacons):

  • WWV Propagation Monitoring: Hams listened to WWV signals on different frequencies (2.5, 5, 10, 15, and 20 MHz). The strength of the signal provided a rough estimate of how well certain bands were propagating, helping operators decide which frequencies to use.
  • Beacon Stations: Operators tuned to beacon stations operating on different frequencies around the world. By monitoring when these signals were heard, they could get a sense of global propagation conditions.
  • Sunspot Numbers: Many hams used published sunspot data and predictions to estimate the effectiveness of different HF bands.

Today (Using Online Tools and Real-Time Data):

  • Real-Time Propagation Maps: Websites and apps like PSKReporter, DXMAPS, Reverse Beacon Network (RBN), and WSPRnet provide real-time data on where signals are being received and which bands are open. These platforms track signal reports and provide a visual display of current propagation conditions.
  • Solar and Geomagnetic Data: Many hams now use online services that provide real-time solar flux, geomagnetic indices, and space weather data. Websites like Space Weather Prediction Center (SWPC) offer detailed insights into how solar activity is affecting the ionosphere.
  • Cluster Networks: DX cluster networks provide real-time information on stations spotted around the world, giving hams direct feedback on current band conditions.
  • Software Tools: Advanced propagation software like VOACAP or HamCAP allows operators to model HF propagation based on real-time data, including solar activity, time of day, and location.

Summary of Key Differences:

While older methods like WWV are still valuable, modern technology has automated and refined many of these tasks, making it easier and more precise for amateur radio operators to ensure their equipment is accurate and their communication effective.

NISTTime and Frequency Services

Radio Amateurs Developing Skills Worldwide