SELCAL or Selective Calling is a function that allows a ground radio operator to alert an aircraft crew that the operator wishes to communicate with that aircraft. Because of the background noise level experienced on HF (High Frequency) radio frequencies, pilots usually prefer to turn down the audio level of their HF receiver until alerted via Selcal. When the ground station operator wants to communicate with the aircraft, they enter into the Selcal encoder the four letter code of that aircraft. This four letter code is usually included in the aircraft's flight plan and it is transmitted over the assigned radio channel. All aircraft monitoring that specific channel receive the Selcal broadcast but only those that have been programmed with that four letter code will respond by sounding a chime or some other alert for the crew.

None, they represent the same unit. Original King Radio part numbers were 9 digits. For example, 066-3056-01. During the Bendix and King merger (i.e. Bendix/King), a new part numbering system was created that converted these 9 digit part numbers to 12 digits. Therefore, 066-3056-01 became 066-03056-0001. Despite this numbering change, units that were originally from the King Radio design still have the 9 digit part number format on the unit dataplate. The 12 digit format for King units appears to be used for catalog and internal Honeywell purposes only. Therefore, any unit that has a zero in its third to last number (i.e. XXX-XXXX-X0XX) has a 9 digit part number (i.e. XXX-XXXX-XXX) on its dataplate / ID Plate.

P serial number KHF-950 units are normally initial production units without most recommended service bulletins or product improvements. Most P serial number units still available on the avionics aftermarket are in poor condition and can be very unreliable.

Serial number 1500 and below limits the component interface availability of the system and in the aircraft. That is, all of the units in the system must be below 1500 in order for a complete system to function correctly. In addition, these serial numbers indicate older units which cause reliability issues.

In January 1989 Bendix/King changed from a nine digit to a twelve digit part numbering system. The new, larger 12 digit numbers allowed for the inclusion of software version into the last two digits of the part number for certain units in which software changed frequently such as EFIS and TCAS processors. Therefore, the two digits immediately preceding the software version indicate the hardware version of the unit.

Different software versions imply different operational features and/or interface capabilities and software modifications imply software repairs (bug fixes) to insure proper operation of these features and interfaces. Software version upgrades frequently require hardware modifications to the unit. Such hardware modifications accompanying software version upgrades do not necessarily change the hardware version of the unit.

Yes, with the appropriate equipment, hardware, antenna, and installation considerations.

A shorted tranline often referred to as "towel bar" antennas are best suited for helicopter applications. Towel bar antennas are attached parallel to the tailboom and fed in on the forward end (please see below example). Very specific instructions in relation to spacing, antenna construction, length, and mounting surface should be followed in order to minimize poor efficiencies at the low frequencies.



Since the towel bar style antenna is considered a short or shunt type HF antenna, the -02 version of the KAC-952 antenna coupler along with the KA-161 external capacitor must be utilized in this type of installation.

In certain installations, a towel bar style antenna may not be possible. Therefore, the KA-98 probe antenna may be used in the KHF-950 system. The same installation considerations (as mentioned above) would need to be observed since all short antennas provide poor efficiencies at low frequencies. A rod style antenna element is installed onto the front of the KA-98 (see picture below). It is important that the probe antenna be provided with a good RF ground. Therefore, the coax feedline from the KAC-952 coupler to the KA-98 cannot exceed 18 inches. In addition, the KA-98 can only be used with the -02 version of the KAC-952 and the KA-161 external capacitor to allow the antenna to tune more efficiently.

If this 18 inch requirement cannot be met, then the KHF-990 HF system should be considered since the amplifier is built in to the KAC-992 probe antenna coupler.

Can the KAC-992 probe antenna coupler be used with a KHF-950 system?

No. The following is a detailed explanation of some of the technical aspects within the KHF-950 and KHF-990 that prevent the KAC-992 from being used in the KHF-950 system.

The standard KHF-950 consists of the KCU-951 Control, KTR-953 Receiver Exciter, and KAC-952 Power Amplifier/Coupler.

In the transmit mode of operation, the KTR-953 provides a low power (milliwatts) signal (at the selected frequency) to the KAC-952. This excitation signal is amplified in the KAC-952 to provide the rated output power (watts). The power amplifier is contained in the KAC-952. The KAC-952 also tunes the antenna to the desired frequency by electronically varying the antenna’s length.

The standard KHF-990 system consists of a KFS-594 control, KTR-993 R/T, and KAC-992 probe antenna coupler.

The receiver/exciter and power amplifier is contained in the KTR-993. The output of the KTR-993 is the amplified RF signal at the rated power (watts). The KAC-992 is strictly an antenna tuner and provides no amplification. Also, the KTR-953 would not provide the commands required to initiate the tuning cycle.

If the KTR-953 was installed with a KAC-992, the output of the KTR-953 would not supply adequate power to drive the KAC-992. Even if it was able to tune, the output power would be millwatts (1/1000) instead of a hundred watts.

For most Cessna Citation models, the following Dayton Granger parts will serve as a suitable HF antenna:

5ARM300-11C Tension Unit
14379 Anti-Precip Wire (30 feet)
16390 Feedthru Assembly
3280 Anchor Kit

Please search individual parts on SEA's website for pricing.

Many of the tuning problems with the KHF-950 are related to improper antenna installation. Here are a few possibilities:

• Poor connection on antenna feed thru.
  
  
• Long wire broken (a wire can crack and not be visible because of the thick insulation)
  
  
• For a short antenna run where the termination point is grounded, the ground may have become disconnected
  
  
• The wire from the KAC-952 coupler to the antenna should only be 6 inches ideally. A length of 18 inches is the absolute maximum. If the antenna feedline is longer than this, the efficiency of the KAC-952 will be greatly reduced possibly causing tuning failures at certain frequencies.
  
  

In some cases, the KTR-953 could be at fault but not likely in most cases. If the tune cycle starts, then the KTR is providing ample power to the KAC. If the tune cycle never starts and the system immediately goes into tune faulty (beeping tone in headset) when the PTT is activated, then the KTR most likely is faulty.

Yes, the KTR-953 receiver/exciter and KAC-952 antenna coupler can be mounted in different locations but problems may be encountered as a result. When the KTR-953 and KAC-952 are mounted in different locations, transmitter distortion and common mode rejection can be encountered within the system. Other symptoms might include:

• Display flashing intermittently when the user tries to tune the HF
• Audio distorted when transmitting on AM or SSB
• Output power low and varies when measured with wattmeter

If the KTR-953 and KAC-952 must be mounted more than 3 feet apart, then there are 3 Service Bulletins that should be incorporated into these units.

• KTR-953 Service Bulletin 8 is effective for units S/N 29974 and below. This SB consists of removing several parts, install some wires, and mounting an feedback board into the unit
• KAC-952 Service Bulletin 9 is effective for units S/N 14332 and below or units with an older control board. This SB consists of make changes to the ALC circuit.
• KAC-952 Service Bulletin 10 is effective for units S/N 14884 and below or units with an older control board. This SB is a continuation of the modifications performed on KAC-952 SB 9 and consists of replacing several resistors and capacitors in the unit.

All 3 service bulletins are recommended for this installation condition. All 3 service bulletins are interdependent of each other and must all be installed for the system to function properly under these circumstances.

For more information on these modifications, please contact an SEA service representative today.

Negotiating the exchange price of a unit only limits the allowable repair cap for the core unit. Southeast Aerospace's exchange transactions are based on the return of economically repairable core unit. Once the core is received and evaluated, the core repair cost incurred by SEA cannot exceed 80% of the original exchange price. That is, it cannot cost SEA more than 80% of the original OH/SV exchange price collected from the customer. Therefore, when and if an SEA exchange price is discounted, there is a risk that additional charges may be assessed once the core is returned and evaluated.

For more information, please refer to these other Exchange FAQs

KTR-953 Service Bulletin 4 addressed the replacement of the original crystal over assembly in the unit with a more accurate, higher reliability Temperature Compensated Crystal Oscillator (TCXO) assembly. The TCXO provides instant-on operation eliminating the need for the 2-3 minute warm up time as with the original crystal oven assemblies. The effectivity for this SB is as follows:

• KTR-953 P/N 064-1015-00 units with serial number 3196 and above have SB 4 incorporated during original manufacturing.
  
  
• KTR-953 P/N 064-1015-00 units with serial numbers between 2940-3195 have SB 4 incorporated during original manufacturing but were not stamped.
  
  
• KTR-953 P/N 064-1015-01 units with serial number 25644 and above have SB 4 incorporated during original manufacturing.
  
  
• KTR-953 P/N 064-1015-01 units with serial numbers between 25350-25643 have SB 4 incorporated during original manufacturing but were not stamped.

The cost to incorporate SB 4 is approximately $2000 (2010 pricing).

While KTR-953 SB 4 is not specifically a required mod, it is unfeasible to offer warranty on a unit without the SB incorporated. Therefore, purchasing and exchange criteria must be accounted for when accepting a unit without SB 4.

Selective Calling or SELCAL is a technique by which an aircraft has a unique identifier and a ground station can contact the aircraft for communication. This eliminates the aircraft crew from monitoring the HF frequencies on a regular basis and the subsequent background noise as a result. The High Frequency Communications system (HF) must have SELCAL capability to process the ground station contact and alert the crew through audio or visual means. One of the components in the SELCAL system is a decoder. The decoder allows a ground station equipped with tone encoding equipment to call the specific aircraft by transmitting 2 pairs of assigned audio tones. The decoder is set to respond to the specific code assignment set on the front of the decoder. Upon reception of the tone code, the decoder signals the HF system that a message is waiting through audio or visual means. Decoders are available in remote and panel mount variations. Some decoders may have the ability to monitor as few as 2 communication radios or up to 5 simultaneously.

In most cases, a Supplemental Type Certificate is not required for the installation of an HF system. Major changes or alterations to an aircraft may include those which affect weight, balance, structural aspects, reliability, operational characteristics, airworthiness characteristics, etc. Some major alterations can be performed using the FAA Form 337 with approved data. This approved data can be in the form of engineering data with a FAA designee approval (i.e. DER, DAR). The DER or DAR then issues an FAA Form 8110 which is considered approved data adequate to proceed with the installation.

HF installations in the USA are installed and approved in the method detailed above. STCs are not required for almost all HF installations since the change to the existing aircraft Type Certificate (TC) is not so intensive as to require one.

Previously, SEA answered the FAQ "...can the KTR-953 and KAC-952 be mounted in different locations in an aircraft". The answer to that question details the service bulletin (mod) levels that each unit must have incorporated for this installation scenario to be possible.

In addition to what these service bulletins offer in the way of installation flexibility, improper performance and actual unit failure can occur if the units are mismatched. KTR-953 units with SB 8 should only be paired with KAC-952 units with SB 9 & 10. KTR-953 without Mod 8 should only be paired with KAC-952 units without SB 9 & 10. Southeast Aerospace has actually seen units fail in the field when mismatched in this manner as well.