Applications
Military and paramilitary users who require HF communications for Long Range Reconnaissance Patrol (LRRP) and Rear Link applications, are frequently faced with enemies which are capable of deploying EW systems.
Aid/relief organizations and peace-enforcement agencies may be seriously compromised in their operations, through interception and jamming of radio traffic from elements within a technically aware population.
A growing problem for military and aid organizations alike is the proliferation of low cost amateur HF radios, which can be easily modified for interception and jamming.
The HF-90 Transceiver, fitted with the frequency hopping option, presents an immediate, cost effective solution to these problems.
Features of the HF-90 HF Frequency Hopping Option
This photograph shows the Frequency Hopping Module which is integral within the Q-MAC HF-90 HF SSB Transceiver, together with the associated microprocessor.
Hopping rate and bandwidth
The Q-MAC HF-90 Frequency Hopping Option has a hop rate of 5 hops per second and operates within a 256kHz bandwidth (hop band). There are 103 contiguous hop bands within the range 2-30MHz. The reference frequency which is selected for use by the operator determines which of the hop bands is selected. Several individual hopping networks can operate effectively (and with minimal interference to other networks) within the same hop band.
The hop speed and bandwidth have been rigorously tested and optimized for the following parameters: voice security, voice clarity, antenna bandwidth and propagation.
Pseudo-random hopping
A pseudo-random (DES) frequency hopping algorithm provides the user with 7.2 x 1016 different hopping codes. This results in a sequence repeat time of 457 million years, ensuring a high level of security.
Robust anti-jam algorithm
All EW techniques (such as detection, direction finding, unauthorized monitoring and jamming) are effectively countered by the HF-90's frequency hopping algorithm. Even in the presence of badly corrupted synchronization data, the demodulation algorithm, combined with the FEC coding and time frequency diversity, provides a robust anti-jam capability.
Rapid synchronization
The HF-90 Frequency Hopping Option offers rapid synchronization on late entry ie. where a network is already communicating in frequency hopping mode and an additional operator wishes to join the network. Synchronization time varies between 6 and 53 seconds (with an average of 26 seconds). Synchronization time on start-up is even more rapid, given that between 3 and 4 synchronization bursts are transmitted within the first 60 seconds of start-up. Synchronization time varies due to the pseudo random time and frequency allocation of synchronization data (bursts) sent from the Master to the Slaves.
Secure code entry
A unique hopping code, comprising 11 digits, must be entered by the operator from the DTMF microphone/handset keypad. The same code must be entered for each Q-MAC HF-90 HF Transceiver operating within the network. The same reference frequency and sideband (USB/LSB) must also be selected. Once entered, there is no way to retrieve the 11-digit code, thus making the code fully secure. Typically this code would be changed on a regular basis (eg. once every month during peace time and once every week during combat).
Increased security through use of SSB voice
In order to mount an electronic attack on a frequency hopping network, an Electronic Counter Measures (ECM) Unit must first identify the presence of the hopping network within a defined frequency range. The ECM Unit must then attempt to determine the geographic location of the hopping network and either crack the hop code or follow and jam the transmissions.
The HF spectrum is typically very crowded and contains a myriad of signals and noise. Therefore, in identifying a hopping network, the task is made easier if the transmissions have a coherent or characteristic signature. For example, frequency hopping transceivers which use digitized voice transmissions employ Phase Shift Keying (PSK) or Frequency Shift Keying (FSK). Such transmissions are well defined and readily identifiable.
The HF-90 (unlike many other HF frequency hopping transceivers) uses SSB voice as opposed to digitized voice transmissions. The instantaneous spectrum of an SSB voice transmission is characteristically 'noise' like. Furthermore, there is no output whatsoever between syllables. This renders the Q-MAC HF-90 extremely difficult to intercept.
These differences become more apparent when observing transmissions over time (using a spectrum analyser set to Peak Hold or Accumulate). With a digitized hopper, the hop channels are easily identified since the output is nearly constant. In comparison, the hop channels of an SSB hopper are more difficult to identify, since on many channels there is no output due to the voice cadence. Synchronization channels may appear as discrete line spectra, given that the synchronization bursts are sent in random timeslots over a number of channels using FSK.
Smart hopping
When using HF on sky-wave circuits at night, many channels are blocked by strong broadcasting and fixed stations. This factor, combined with fading and multi-path propagation, leads to a very hostile HF environment. Enemy jamming within the hop set further compounds this problem. The Q-MAC HF-90 Frequency Hopping Option overcomes these difficulties through "Smart Hopping".
Smart Hopping enables avoidance of blocked channels. The network acquires information on the signal strength of each channel within the hop set. All network members receive this data automatically and consequently blocked channels are avoided. Continuous updating occurs in order that changing band conditions are accommodated.
Simple operation
Despite its complex design, the hopping function within the Q-MAC HF-90 HF SSB Transceiver is extremely simple to operate. It is accessed from a single key on the front panel.
The transceiver display clearly indicates fixed/hopping status at all times. The following modes are differentiated:
- Fixed frequency mode
- Hopping mode not synchronized
- Hopping mode synchronized (receiving sync bursts)
- Hopping mode synchronized (no longer receiving sync bursts)
- Setup parameters (including Slave/Base setting, Smart Hopping status and the 11-digit hopping code) are entered via the DTMF microphone/handset keypad.
Selcall facility in hopping mode
The Q-MAC HF-90 HF Transceiver incorporates a Selcall facility which can be used in frequency hopping mode, as well as on a fixed channel. When operating in frequency hopping mode, Selcalls may only be sent/received between transceivers within the hopping network.
Low power consumption
The Q-MAC HF-90 HF Transceiver is very power efficient in frequency hopping mode, given that it employs SSB for voice transmissions. With SSB there is no output between speech syllables, whereas alternative digital methods produce output continuously on speech. The low power consumption of the Q-MAC HF-90 HF SSB Transceiver means it is ideally suited to manpack/portable roles.
Retrofitting to early version HF-90s
The Q-MAC HF-90 Frequency Hopping Option may be ordered together with the HF-90 HF Transceiver, in which case it is provided as an integral module within the transceiver. Upgrade kits are also available for retrofitting this option to existing HF-90 Transceivers.
Frequency Hopping Specifications
(Note: For a description and specification details of the Q-MAC HF-90 transceiver, select Q-MAC HF-90 Specifications.)
|
Mode
|
SSB (J3E) speech plus FSK sync |
|
Hop bandwidth
|
256kHz (approx 1/4 MHz)
|
|
Number of hop bands
|
103 contiguous bands in the range 2-30MHz |
|
Hop band selection possible
|
Yes (reference frequency determines which pre-set hop band is utilized) |
| Hop sequence |
Pseudo-random
|
|
Sync burst repetition rate
|
Pseudo-random
|
|
Late entry
|
Possible |
| Sync channel allocation |
Random at time of code selection
|
| Hop code entry |
Via DTMF mic/handset keypad
|
| Number of code combinations |
7.2 x 1016
|
| Hop algorithm |
Modified DES |
Please note that export of this product requires an Export Permit (issued by the Australian Department of Defence). In order to obtain this Permit, customers can assist us by completing the form titled "Statement by Ultimate Consignee or Purchaser". The issuing of the Export Permit usually takes 30 working days. Customers should be aware of this requirement when placing orders.
Frequency Hopping | HF Transceiver
