How to Use RF Gain, Noise Blanker, and Other Transceiver Features to Improve Copy by Mark Haverstock, K8MSH
| How to Use RF Gain, Noise Blanker, and Other Transceiver Features to Improve CopyMark Haverstock, K8MSH Even credit card operators need to understand how the controls work to help them improve reception of ham signals. There will always be some kind of ambient noise on the HF bands. It may be either man-made (QRM) such as pulse noises from vehicle ignitions or natural (QRN) like lightning. You probably have heard the old ham saying, “You can’t work ‘em if you can’t hear ‘em.” When we can’t hear signals well, it’s easy to miss a lot of potential contacts–or even some rare DX. So how can you improve your odds? Just about all brands of HF radios have features that will help reduce noise and improve your ability to hear signals. I’ll be referring to controls you’ll find on the Icom IC-7300 HF Plus 50 MHz Transceiver, a very popular rig. You’ll find the same or similar controls on most transceivers. The best way to learn how to use these features is to get on the air and experiment with them. Once you’ve discovered which ones best suit your needs, make them part of your regular operating routine. RF Gain>Helps separate signal from noise You’d think cranking the RF Gain fully clockwise would help improve your reception. I used to think so. But as it increases signal strength, it also increases the noise level. A better strategy is to “ride” the RF Gain. Proper control of the RF Gain is one of the most powerful tools a ham has for digging weak signals out of the noise. As counterintuitive as it seems, by turning down the RF Gain and increasing the AF Gain, you can sometimes pull out a signal that was previously in the noise. The human ear is a great discriminator. If the receive signal level is reduced enough that the background noise is lessened, then the audio level can be increased to a point where you can hear the signal better.The purpose of the RF Gain control is to allow the operator to limit the range of the AGC (Automatic Gain Control) to some degree. With the IC-7300 tuned to a signal, turn the RF Gain to the 11 o’clock position, turn the AF up to a comfortable volume, then turn the RF Gain down until the background noise nearly disappears. Adjust the AF control as needed to the optimum audio level. Noise Blanker (NB)>Reduces/removes pulse noise The Noise Blanker eliminates pulse-type interference like the noise from car ignitions and other man-made sources. They have no effect on reducing naturally occurring, ever-present atmospheric noise. How does it work? A Noise Blanker samples an off-the-air signal at a very wide bandwidth. If a noise pulse is found, it briefly turns off the audio to the receiver for the duration of the pulse and passes the remainder of the signal. The Noise Blanker becomes considerably more effective at larger bandwidths as long as there are no strong signals present in the passband. The NB produces some distortion on sideband signals, but it improves overall copy. On the IC-7300, pushing the NB button for one second opens the Noise Blanker menu on the right side of the display. There are three setting options: Level (level where the Noise Blanker activates, 0-100), Depth (noise attenuation level, 1-10), and Width (blanking duration time, 1-100). It’s recommended to set the minimum width needed to get rid of pulse noise. Noise Reduction (NR)>Reduces noise/makes signals more readable The Noise Reduction function reduces random noise components and enhances signals that are buried in noise. By removing the noise, the improved audio makes it much easier to understand distant and weak contacts.DSP technology has made it possible to reduce static and white noise, helping to bring signals out of the noise. It uses digital signal processing to analyze the signal and sort noise from signal, reducing what it determines to be noise. In the process, some distortion is created. The higher you set the NR level/algorithm, the more hollow and distorted the audio on sideband. But the technology continues to improve as new radios come on the market, making voices sound more natural. On the IC-7300, pushing the NR button for one second opens the noise reduction menu where you can change the NR level settings (0-15). Twin PBT>Rejects interference from nearby signals In general, the Twin PBT (Passband Tuning) electronically narrows the IF (Intermediate Frequency) passband width by shifting the IF frequency slightly outside of the IF filter passband to reject interference. The IC-7300 uses DSP for the PBT function. You can narrow the IF passband width by rotating both inner (PBT1) and outer (PBT2) Twin PBT controls the opposite direction from each other. A pop-up window graphically lets you watch the filter response changing width and moving signals around within the passband. There are three default filter options available through the touch screen, as well as continuously variable bandwidth settings in the filter menu, accessed by holding the FIL button at the top center of the screen. CW bandwidth is adjustable using the tuning knob, and sharp or soft skirts can be selected for all modes.  Notch Filter>Removes interference from inside passband A Notch Filter is relatively narrow and removes a specific “chunk” of signal such as annoying heterodyne tones, tuner-uppers, etc. The filter is tuned to match the specific audio frequency of the interference. The IC-7300 has both Auto Notch and Manual Notch functions. Auto Notch is used in the SSB, AM, and FM modes; Manual Notch in the SSB, CW, RTTY, and AM modes. Pressing NOTCHlets you choose AN (Auto Notch), MN (Manual Notch), or off. AN automatically attenuates unwanted signal. The Manual Notch attenuates by adjusting a frequency. Pushing WIDTH sets the Manual Notch filter width to WIDE, MID, or NAR. Slowly adjust POSITION to manually attenuate the frequency. Notice the blank space in the below photo of the audio scope between 2-3KHz which was removed.  Preamp/Attenuator> Amplifies or reduces signal levelPreamps amplify signals in the receiver front end to improve sensitivity. A preamp is generally used when attempting to boost weak signals. If you use the preamp while receiving strong signals, the signal may be distorted. In this situation, turn off the preamp or activate the attenuator. The IC-7300 has two preamps and an attenuator. To activate the preamp, push the P.AMP button; each push goes from P.AMP1 (most effective for HF bands) to P.AMP2 (most effective for 50MHz) to off. P.AMP1 does a reasonable job of improving copy without degrading signal to noise ratio. The attenuator (ATT) prevents a received signal from becoming distorted when a very strong signal is near the frequency, or when a very strong electric field is near you (such as an AM broadcast station). Hold down the P.AMP/ATT button for one second to turn on the attenuator, and hold it down again to turn off the attenuator. Go to the Source These radio features can be very effective at reducing noise, but don’t overlook the obvious. Be sure everything is properly grounded and ferrites/chokes are used where applicable.Also, take steps to reduce or eliminate the amount of noise generated in your environment whenever possible. Eliminating local noise sources and using your rig’s noise reduction features will increase your ability to copy signals significantly. |
Spanish Sharpshooter teams trained in a forest environment, improving their shooting stances and surveillance capabilities, as part of NATO exercise Noble Jump 2017. They also practised transferring data and images using HF radios, some of these being sent back directly to Spain’s Special Forces command.Speaking to Armada International at the SOF Industry Conference on 12 May 2020, Program Executive Officer for Command, Control, Communications and Computers (C4), Deb Woods spoke of the updated plans to equip the US Special Operations Command (USSOCOM) with a next-generation HF solution.“Partnerships are ongoing with the services including the US Navy regarding a government owned wideband [HF) waveform. As well as capabilities we have today, we want to take advantage of smaller SDRs to provide a government-owned kit to support SOF whether they are operating in some kind of unconventional warfare or working with partner national forces who also want a wideband capability,” she told Armada.As of 18 September 2020, the USSOCOM has yet to publicly release a requirement regarding the procurement of a next-generation HF SDR.A former French SOF operator now working in the industry, also confirmed to Armada this so-called “resurgence of HF in special operations” over the past few years.Referring back to special operations in the 1990s, which included a focus on People Indicted for War Crimes (PIFWIC) in the former Yugoslavia, the source described how legacy HF radio sets had lacked the required data throughput to support surveillance and reconnaissance missions tasked with the positive identification of war criminals.“The special forces task was simple: Priority Intelligence Requirement (PIR1) was to collect, to find, and to arrest PIFWICs and defer them to ‘The Hague’ international court. To arrest those persons, a track began, and before proceeding to the intervention to arrest them, we had to make sure that it was the correct person, and that the intervention teams had all the details concerning the environment.“The intelligence collected was open source, but human intelligence (HUMINT) was delivered by some commandos hidden during many weeks in difficult conditions close to the alleged criminals house.“At this time, the technology of the radios used permitted teams to send small text messages, but the speed of the data wasn’t good enough to send pictures of the person, which was mandatory before any operations. I remember once, it took me four hours to send a 10kb photo with the resolution of a stamp,” the source continued.“At the same time, satellite communication systems emerged as a technological ‘revolution’, especially INMARSAT with Mini M satellite terminals. Small, light, with a pretty good data speed (2,400bps), SATCOM started to compete with, and finally replace, HF systems in the field. This was the case few years later in Afghanistan where SATCOM systems were used by SOF to conduct combined operations and definitively buried HF radios, he added.
A US Marine with Marine Rotational Force-Europe 19.2, uses a Norwegian Army AN/PRC-150 radio alongside a Norwegian soldier during high frequency communications training in Norway, during 2019. MRF-E focuses on regional engagements throughout Europe by conducting various exercises, mountain-warfare training, and military-to-military engagements, NATO SOF units rely upon HF SDR technology to not only ensure connectivity in contested environments but also cost-effective interoperability with partner nation forces.Since then, HF has witnessed a series of enhancements which have significantly changed the opinion of SOF operators considering utility of the SDR type.These include decreased SDR weights to less than 5kg; increased radio autonomy providing operators with up to 72 hours use on a single battery; the full spectrum of types of calls including voice, text, GPS request and sending; increased data speeds with robust waveforms using 3G ALE technology; and finally, easy to use software for programming and data.“And probably the most important point – no need to be trained over several months to use those ‘smart radios’ due to ease of use interfaces like a smartphone. If the signaller of the commando team is killed in action or wounded, any of his team partners would be able to use the radio,” the source stated.Additional benefits include the cost-free nature of HF, which bounces signals off the Ionosphere rather than relying upon expensive leasing or ownership of geo-stationary satellites.“Special forces members are not dependent upon any third nation or any satellite operator. So while SATCOM will not disappear from a SOF small unit team, HF is now in a position to supplant it,” the source concluded.Solutions currently available to SOF include Codan Communications’ 6110-MP which is part of the company’s Sentry-H family of products, designed to meet the demands of the “modern battlefield whilst offering full backwards compatibility with legacy products”, according to Codan literature.“The 6110-MP is one of the smallest, lightest form factor manpack HF radios available, without compromise on capabilities. It delivers a rugged SDR solution for military organisations that demand uncompromised, secure voice and data communications, while on the move,” a company statement explained.The manpack, which provides a power output of 30W, has a maximum battery life of up to 79 hours dependent upon operational utility. Comprising less than 4.7kg in weight, the SDR is ruggedised up to MIL-STD-810G standards.The solution also includes an embedded GPS in addition to IP connectivity over Ethernet/WiFi and USB. Encryption is provided by AES-256 and CES-128 communications security.According to Felix Wickenhäuser, technology consultant at military radio communications specialist JK Defence & Security Products, HF SDRs provide reliable and long range communications for SOF teams operating at reach and in complex operating environments such as the Arctic or mountainous areas where it can be hard to acquire a satellite signal due to physical barriers.“Things even worsen once a near-peer adversary has qualified EW-assets. Especially then, waveforms featuring so called LPI / LPD (low-probability of interception/detection) methods are a critical advantage,” Wickenhäuser explained.“Satellite communications are also vulnerable to space kill-vehicles or counter-satellite missiles. Furthermore the operation of HF radios does not require costly infrastructure,” he said.“The market is heading for higher data rates along with even smaller form factors, such as HF-handheld radios. This allows the implementation of entirely new concepts of operation, as the communication at the tactical edge is no longer limited to shorter-range V/UHF radios.“From a technical point of view, we will see direct-sampling architectures as the foundation of even more advanced waveforms / transmission methods. Even though higher data rates are mostly played as the key advantage of modern HF radios, this is only half the truth. “Wideband HF also allows for even more advanced error correction algorithms thus allowing more robust links even under very challenging channel conditions. It is important to also consider this side of things. Usually you see a trade-off between data rate (payload) and robustness,” he continued.JK Defence and Security Products is partnered in Germany with L3Harris Technologies which has designed the AN/PRC-160 as a next-generation HF SDR that is already in service with multiple undisclosed SOF units in Europe.As Wickenhäuser explained: “The PRC-160 is at the forefront of the HF radio revolution. Its intuitive operation along with even higher data rates make it a future-proof package. Designed as a system, matching body-worn antennas provide best possible transmission. Furthermore the PRC-160 is compatible with already fielded accessories like handsets, batteries, base-stations and remote-controls. Known MMI concepts also apply to this radio.“Its NSA-certified Type-1 cryptology also allows secure interoperability with NATO partners. Being a multiband transceiver the radio can also communicate in the widely used VHF-band. This multiband system is also the world’s first and only HF manpack meeting new NSA crypto-modernisation standards,” he concluded.According to L3Harris literature, the AN/PRC-160 provides data rates up to 10X higher than legacy HF radios, as well as enhancing interoperability between US and coalition force elements across a battlespace.Operating between 1.5-60MHz, the AN/PRC-160 provides a power output of 20W in HF mode, providing data rates up to 120kbps supported by optimal channel selection which responds to real-time conditions.
L3Harris Technologies’ AN/PRC-160 is in use with multiple SOF units around the world thanks to its increased throughput and reduced form factor.The SDR includes embedded SAASM or commercial GPS receiver to ensure accurate Position Location Information for enhanced Situational Awareness.Finally, Barrett Communications offers up its latest HF solution- the PRC-4090- with chief executive officer, Andrew Burt describing how HF solutions provide a cheaper and easier to use solution for SOF and their partner nation forces around the world.“HF networks do not require the infrastructure of SATCOM which means countries including the US are reinvesting in HF as the backbone of key infrastructure. This is why HF lends itself ideally to military operations as well as homeland security, emergency services and critical national infrastructure as a last resort communications capability.“HF can be readily deployable, providing end users with an immediacy in communications they are unable to achieve with other communications mediums in that first instance,” Burt continued while hailing its utility to support special operations at the tactical edge.The PRC-4090 was unveiled to the market at DSEi in September 2019, following its development on the back of the 4000-series of SDRs by Barrett Communications. Capable of providing SOF small unit teams with secure email, data transfer and telephone connectivity over the HF networks, in addition to 4G LTE and MANET networks, the transceiver can be controlled by smartphone, tablet or laptop using Barrett’s 4000 Series HF Remote Control App.Operating between 1.6MHz-30MHz in Tx; and 250-KHz-30MHz in Rx frequency ranges, the PRC-4090 retains the capacity to manage up to 1,000 channels. The PRC-4090 platform is capable of transmitting in power outputs of 10, 30 and 150 Watts with optional transportable high power amplifier options up to 1kW.The PRC-4090 also comes with options for Advanced Frequency Hopping technology, providing operators with between 5 and 25 hops per second as well as an 8-digit hopping encryption key- a capability which Burt declares as providing “excellent protection against EW attacks”.The SDR can be attached to personal load carrying equipment for dismounted special operations. Furthermore, the radio can also be attached onto a tactical docking station for integration on board special operations vehicles.Full Rate production of the PRC-4090 was started in the third quarter of 2020, Burt confirmed.
ve3ips 