About Modems

HAL Communications Corp. has been designing and manufacturing high-quality, easy to use radio data communication products since 1972, with our modem solutions used in networks covering large geographic regions.

Now in our fifth decade of operation, HAL Communications Corp. has refined its CLOVER high-performance protocol into an advanced digital modem waveform and protocol specifically designed to pass data at the highest possible rate via standard High Frequency (HF) radio equipment. Recognizing that HF radio signal propagation may induce severe distortion, CLOVER employs extraordinary measures to compensate for this distortion and maximize the data throughput rate.

With two distinct variants – CLOVER 2000 and CLOVER 2500 – our protocol has an array of features designed to ensure performance, reliability and usability. These include:

● High throughput and adaptive ARQ
Unlike simple one- or two-rate adaptive ARQ schemes, CLOVER switches between six-rate adaptive speed levels. Signal parameters for both local and remote stations are actively measured in real-time and transmit modulation is always set directly by the receiving station within seconds to a mode that will work.
CLOVER also uses two-level ARQ protocol, sending system control information in the CLOVER Control Block (CCB) using a very robust modulation format and formats data blocks in 256 byte blocks using the modulation format that matches current conditions.

● Error-correction coding
CLOVER protocol incorporates error-correction encoding of all transmitted data. The Reed-Solomon code is used because of its superior ability to correct burst errors that are typical for HF communications paths. CLOVER only requires repeat transmission of data blocks where errors have exceeded the capacity of the Reed-Solomon coding.
All data sent via CLOVER is encoded as 8-bit data bytes and the error-correction coding and modulation formatting processes are transparent to the data stream – every bit of source data is delivered without modification to the receiving terminal. Compressed or encrypted data may therefore be sent without the need to insert (and filter) additional control characters and without concern for data integrity.

● Selective ARQ Repeat
Unlike other block or packet ARQ protocols, CLOVER does not repeat data which has been received correctly. CLOVER buffers all received data packets and repeats only those packets that cannot be fixed with Reed-Solomon coding.

● Bi-directional ARQ
Most ARQ protocols designed for use with HF radio systems can send data in only one direction at a time. With CLOVER, however, data may flow in both directions at the same time. The CLOVER ARQ time frame automatically adjusts to match the data volume to be sent in either or both directions.
This feature provides the benefit of full duplex data transfer but requires use of only simplex frequencies and half-duplex radio equipment. This two-way feature of CLOVER can also be used as a back-channel order-wire command mode. Either or both stations will shift back to CCB level when all buffered data has been sent. In this chat mode, relatively slow communications may be maintained at a rate of approximately 6 characters-per-second, making it a more efficient mode for keyboard-to-keyboard communications.

Key differences between CLOVER 2000 and CLOVER 2500

Bandwidth 2,000 Hz, (500-2,500 @ -50 dB)
Data Rate 3,000 bits/sec
ARQ Data Rate 220 to 2,000 bits/sec
Broadcast Data Rate 112 to 1,336 bits/sec
Bandwidth 2,500 Hz, (250-2,750 @ -50 dB)
Data Rate 3,750 bits/sec
ARQ Data Rate 275 to 2,500 bits/sec
Broadcast Data Rate 135 to 1,667 bits/sec

Selecting the right HF modem from HAL Communications Corp.

Each of HAL Communications Corp’s modems is compatible with CLOVER 2000 and CLOVER 2500 as well as AFSK waveforms. HAL provides three distinct modem options, however, with each designed to suit the needs of particular applications.

● DSP4100/2K
A sturdy and reliable HF radio DSP modem, the DSP4100/2K is the larger of HAL’s modems, with a footprint of 5.5×8.7×1.5″ (14.0×22.1×3.8cm) and a weight of 1.5 lbs (0.7 kg). Designed as an all-purpose solution where portability is not an immediately pressing concern, it’s an effective choice for most applications. The DSP4100/2K features serial RS-232 connectivity to the PC.

● DSP4200/2K
For applications where portability is more of a factor, the DSP4200/2K features a much smaller size – 1.25×4.20×6.15″ (3.2×10.7×15.6cm) at just 0.8 lbs (0.37kg) of weight. The DSP4200/2K also features a USB 2.0 connection to PC for both data transfer and powering the unit, as well as field-upgradeable firmware, providing a more modern and easily transportable solution.

● M4200
Featuring the same capabilities as the DSP4200/2K, the M4200 HF tactical modem is designed for use in more challenging environmental conditions. Waterproof connectors protect the unit from unpredictable weather elements, while a ruggedized, sealed enclosure ensures that the M4200 can stand up to harsh conditions with greater reliability and longevity.
With five decades in the radio communications industry, HAL Communications Corp. is considered a world leader in HF radio modem and digital transmission technology, and remains committed to its core values – quality products, easy-to-use systems and excellent customer service.

● MB5100/2K, HF IMAP Mailbox
The HAL Communications Corp. MB5100/2K, HF IMAP Mailbox solution, provides email traffic to any email address worldwide over HF radio. The HF Mailbox acts as an Internet gateway, providing a seamless portal to and from the Internet and HF radio network.

The HF IMAP Mailbox is a modem solution built to meet the demands of today’s increasingly mobile users, with features including:

Advanced synchronization Compatibility and familiarity Automation of manual processes User-configurable link scheduler Security and speed
The embedded mailbox feature provides direct and end-to-end mail synchronization over HF, with no external computers or controllers required over the LAN or Wi-Fi connection. Integration with the user’s preferred mail application is transparent, due to the use of IMAP protocols that allow direct connection to both Android and iOS smartphone and tablet mail apps including Exchange, Outlook, Apple Mail and Gmail via either Wi-Fi or LAN Connection. Sending and receiving of data is no different to sending an email from your phone, tablet or laptop, so training of users is minimal. The HF IMAP Mailbox allows synchronization of email and configuration data wirelessly and automatically, removing many of the manual processes required with legacy solutions. Remote stations are able to be configured over-the-air, making for faster establishment times on the network, and remote control and configuration management affords network managers the ability to add/drop nodes using OTAR (over the air re-programming) without having to configure individual stations. Pre-determined and automated mail delivery can be scheduled at set times according to individual network requirements. Additionally, the Priority and Emergency Messaging feature allows immediate delivery of high-priority messages over lower-priority messages and information. Built-in digital encryption, link security, and automatic file compression ensures email and other traffic is transferred securely in the shortest possible timeframe. Link security and encryption ensure data transfer is possible only between like-coded stations and transmitted data is digitally encrypted. Additionally, the HF IMAP Mailbox transfers mail transparently allowing for customer-specific and third-party data encryption for higher-level data protection requirements.

Based on HAL Communication Corp’s CLOVER 2000 and CLOVER 2500 waveforms with enhanced data throughput rates, all HF connections are managed automatically for many commercial transceiver models allowing fully automatic mail synchronization for 24-hour unattended operation.