Story 16 - HF Log Periodic Antennas

Used by 110 Sig Sqn in South Vietnam

By Denis Hare OAM BEM

Preface

Not long after the School of Signals moved from Balcombe to its new purpose-built buildings at Simpson Barracks, Watsonia in 1970, a training antenna was added to the skyline.  The antenna at the front of the new school would be a beacon for the many members of the Royal Australian Corps of Signals (RASigs) working, attending or returning to the school.  During the Vietnam war, the Log Periodic Antennas (only invented in 1952), was part of the rear link to Australia, for the deployed Australia force, communicating mainly via 6 Sig Regt also at Simpson Barracks.

Introduction

The command and administration rear link used by the Australian Force Vietnam (AFV) to communicate to/from Australia was a very complex high frequency (HF) link, using mostly non-tactical equipment’s.  The equipment’s and antennas used were the same as used by the Australian Communication Army Network (AUSTCAN) ensuring the interface to the main Army tape relay station, located at Watsonia.   Equipment’s and antenna farms were large, deployed over a number of different locations, up to 100km apart, interconnected by cable and trunk VHF/UHF radio links.  The network used lots of technicians and operators to run 24 hours per day to provide the secure telegraph communications circuits to/from Australian for AFV plus in-country communications.

The rear link equipment and locations were reconfigured a number of times during the war, because of location issues, enemy action and equipment improvements, while always maintaining the vital rear link to Australia.  There were always issues with link propagation conditions either in Vietnam or Melbourne.   It is a credit to the many members of RASigs involved plus the teams from 127 Sig Sqn that installed the equipment.  ⁽¹⁾

The first HF Log Periodic Antenna (LPA) used was a Vertical Polarized Log Periodic Antenna (VLPA) constructed from makeshift components at the Saigon Ba Queo Receiver (Rx) Station, because of limited space and the proximity to the Saigon Tan Son Nhut airfield in October 1967.  In the future both VLPA and Horizontal Polarized Log Periodic Antenna (HLPA) would be used with both the Transmitter (Tx) and Rx Stations, during the war.

Situation Early 1968

With the deteriorating security situation in early 1968, an urgent reconfiguration of the rear link network was required in February 1968, with the Saigon BA Queo Receiver (Rx) Station being moved to the large US Army Base at Long Binh because of enemy attacks near the location of the Rx Station. ⁽²⁾    Fire from enemy action at the Saigon Phu Tho Tx Station in May 1968, caused the rear link to be closed for a number of hours because of damage to part of the Tx Stations antennas. ⁽³⁾

 Vietnamese huts burning and a HF Antenna at Phu Tho AUSTCAN Tx Station May 1968. 
Photo supplied by Ian Willoughby.

Plans for the Phu Tho Tx Station were in place, for a new air-conditioned building along with upgraded antennas including a HLPA.  Testing had occurred in Saigon using US Army equipment (Tx and HLPA) on the Melbourne link path to confirm that the planned HLPA was suitable for the AFV rear link. ⁽⁴⁾   Also, part of the plan was a backup site using E513 transmitters ⁽⁵⁾ at the 110 Sig Sqn location, 1^st Australian Logistic Support Group (1ALSG), Vung Tau. ⁽⁶⁾ 

However, with the deteriorating security situation and the high physical risk of the Saigon Phu Tho Tx Station, the Commander AFV (Major General A. L. MacDonald) on the 21^st July 1968 made the decision to move forward plans for HQ 110 Sig Sqn (Force Signals) to relocate to Vung Tau and to relocate the Phu Tho Tx Station to the 1^st Australian Task Force (1ATF) base at Nui Dat.  The Tx Station at Nui Dat was to be operational by the 14^th August 1968.   This solution would allow the AFV vital rear link Tx Station to be physical protection by Australian combat forces. ⁽⁷⁾ 

Tx Station moved to Nui Dat

Stores for AUSTCAN Tx/Rx Stations had already been requested for rebuilds at  Vung Tau (backup Tx), Phu Tho (Tx) plus Long Binh (Rx) and most had arrived at Vung Tau on the HMAS Jeparit ⁽⁸⁾ which included stores for HLPAs. ⁽⁹⁾

Detail planning started on the moves, with the HQ to Vung Tau to be completed no later than 0800hours on 8^th August 1968 and the new Tx Station at Nui Dat commence transmission on the Saigon – Melbourne circuit no later than 7^th  August 1968. ⁽¹⁰⁾

The AUSTCAN Tx station at Nui Dat started continuous operation on the 9^th August 1968 using the newly installed Type 1 rhombic antennas.  The Saigon to Melbourne circuit averaged 19.2 hours up time per day for September 1968, using the transmit functions from Nui Dat, which was reported as satisfactory. ⁽¹¹⁾

      
Photo Left:  Tx Rhombic Type 1 Antennas at Nui Dat Sept 1968. 
Photo supplied by Denis Hare. 
Photo Right:  Tx Station at Nui Dat Oct 1968.  AWM P823.27.12.

       
Photo Left:  Tx HLPA Antenna boom being prepared to lift onto the Mast at
Nui Dat Sept 1968.  Photo supplied by Robert Gilfillan.  
 Photo Right:  Tx HLPA at Nui Dat early 1970. Photo supplied by Tony Roberts.

The Tx Station was operational without the Tx Building completed and the HLPA still under construction.  Tx HLPA was completed at Nui Dat 4^th October 1968, tested and on circuit 24^th  October 1968. ⁽¹²⁾ This remarkable task in moving the Tx Station and other activities while maintaining communications for AFV was done by members of 110 Sig Sqn and 127 Sig Sqn, supported in the task by other members of AFV, including as always, our parent Corps RAE. ^{(13) (14)}   It was a credit to all involved and true to our motto “Swift and Sure”.

Locating large antennas in the Nui Dat area was not an easy decision because of the many helicopter landing zones plus 1ATF was not happy having to have lights on top of the Antenna masts.  But the compromises were, they would be remotely controlled by the 1ATF CP and could be turn on at night for the period any aircraft was operating in the Nui Dat Area.   There was also concern with radio frequency radiation when a soldier was killed by a claymore mine in proximity to the Tx Rhombic Antennas in September 1968.  An investigation concluded that the infantry soldier was carrying the mine armed and he accidentally triggered it. ⁽¹⁵⁾

The maintenance was ongoing at the Tx Station, relocating Antenna feeder routes plus track vehicles cutting cables, lighting strikes and other storm damage was the normal at Nui Dat until the station was relocated to Vung Tau in preparation for the force leaving Vietnam.

Relocating and upgrading Vung Tau

With the HQ, 110 Sig Sqn moving to the 1ALSG base at Vung Tau in August 1968 and the backup Tx Station which now included an VLPA.  ⁽¹⁴⁾  It should be highlighted that 110 Sig Sqn, depending on propagation conditions, used either a VLPA or HLPA at its backup Rx Station in Vung Tau and this enhanced the signal-to-noise ratio between Rx and Tx on the back up rear link.

Other parts of the AUSTCAN system were also moved to Vung Tau, with the AUSTCAN rear link receivers relocated from Long Binh in late 1969.   This reduced system complexity by freeing radio relay equipment’s and manpower.

      
Photo Left:   110 Sig Sqn soldiers preparing Rx HLPA boom to be lifted on to its
mast at Vung Tau in 1968.  AWM P823.015 (Donor K. Fower).  
 Photo Right:   Completed Rx HLPA at Vung Tau in 1968.  
Photo supplied by Ian Willoughby.

The move of the transmitters from Nui Dat to Vung Tau begun in April 1970 with the start of the construction of the new building. ⁽¹⁶⁾    Over the following months antennas (2 x VLPAs) and engineering/installation work resulted with the Tx Station in a new building at 110 Sig Sqn, Vung Tau and working the rear link from 31^st December 1970. ⁽¹⁷⁾  The new Tx building was called ‘Tieng Noi Uc’ (Voice of Australia).

 
E513 Transmitter in the new Tx building at Vung Tau.  AWM EXT/71/075/1/VN.

110 Sig Sqn finally had most of its major communications facilities in Vung Tau with the Saigon Major Relay Station (MRS) relocated to Vung Tau in Oct 1970.

However, on the 8^th January 1971, the new Tx Station at Vung Tau had one of its VLPA knocked down by a RAE bulldozer and 110 Sig Sqn had to reactivate the transmitter still at the old Nui Dat Tx station as the theatre emergency. ⁽¹⁸⁾   In February 1971, a 127 Sig Sqn rigger team arrived again from Singapore to assist in the dismantling of the Nui Dat Tx Station including the two rhombic antennas and the HLPA. ⁽¹⁹⁾  The Nui Dat HLPA was reassembled at Vung Tau in March/April and back in use. ⁽²⁰⁾

Staff Sergeant Bill Burgess, 127 Sig Sqn supervising the construction of the
Tx HLPA (Ex Nui Dat) at  Vung Tau April 1971.  AWM PJE/71/0196/VN

Antenna repairs and maintenance at Vung Tau was an on-going task in the monsoon environment of South Vietnam.   Humid, salt, sand and high winds in the monsoon dry and rains plus typhoons in the monsoon wet. ^{(21) (22)}

Heavy monsoon rain in July 1971 at the 1ALSG base washed sand, damaged roads, buildings and the Rx HLPA.  The antenna was made completely useless and withdrawn from service.  ^{(23) (24)}

 
Part of the 110 Sig Sqn Vung Tau Antenna farm in the sand in early 1971. 
Note the Long Hai Mountains in the background.  Photo supplied by Ivan Bunn.

Decommissioning 1971

On 18^th August 1971 the Prime Minister announced that the force would be withdrawn.  Generally, the resulting Operation Interfuse required to have the combat elements home by Christmas and as much as the logistic element as was prudent. 

The early hard work of relocating all the 110 Sig Sqn facilities to Vung Tau simplified the communication plan for the RASigs units, with the withdrawal of the force through Vung Tau.

The plan was to maintain the existing communications system as long as necessary and to deactivate it piece by piece as the requirement ceased.    

Detailed withdrawal planning for 110 Sig Sqn and communication began. Assistance of the US Army Communications Assets Recovery Agency requested to help packing the electronic equipment.  Early stores for Return to Australia (RTA) shipped on HMAS Jeparit and Q Store activities in full swing locating and recovering equipment. 

The HLPA trolley guy blocks were damaged with earthmoving machinery and the antenna out of action for a period because of a hole in the balun.  110 Sig Sqn also played a major role for 1ATF assessing 104 Sig Sqn to dismantle and relocated from Nui Dat along with 547 Sig Tp, while all the time planning and preparing for the force communication system to be reduced while maintaining  communications for the Australian Army Training Team, Vietnam (AATTV) and a few others that were to remain in Vietnam. ⁽²⁵⁾ 

 
110 Sig Sqn Riggers working on the HLPA in late 1971.
 Photo supplied by Ivan Bunn

Work and testing on a new rear link via Singapore (COMANZUKFOR) and Manila Clarke Airbase (USAF Base) began and there were many engineering issues. 

HQ1ATF now in Vung Tau and in command of the Vung Tau base from October caused problems with demands for work parties from 110 Sig Sqn while trying to dismantle the major part of the force communication system.  Rx HLPA boom was lowered and found to have severely corroded and antenna would have to be written off. ⁽²⁶⁾

127 Sig Sqn from Singapore returned to help.  After inspecting the E513 transmitters, they were written off because it was determined they wouldn’t survive removal back to Australia. ⁽²⁷⁾

Rear link for the Force was cutover to a combination of radio relay (Vietnam), submarine cable (Vietnam to Philippines to Singapore), and HF radio links (Singapore to Australia).  Tx and Rx links closed at Vung Tau 16^th December 1971. Installations, deinstallations, testing, reporting, packing and movement of stores and RTA of personnel all proceeding simultaneously at a hectic pace. The Tx HLPA dismantling started with the boom removed plus 3 x VLPA lowered. ⁽²⁸⁾

Because of corrosion a most novel way was used to remove the Rx HLPA mast using a US Military Sikorsky CH-54 (Skycrane) as a training fight for the cost of a case of amber.  The Mast was lifted and then carried out to sea and dumped.  ^(29)(30)

    
Photos Left and Right:  Skycrane hooking on the Rx HLPA Mast while riggers
unbolt the base Dec 1971.   Both photos supplied by Trevor Hung.

 
Photo Bottom:  Mast being carry out to sea to be dump Dec 1971. 
Photo supplied by Bob Coventry.

Summary

The HF AUSTCAN rear link LPAs in South Vietnam used because of limited field space and area protection requirements at the AFV bases was most successful.  It is a credit to all involved that design, built, operated and maintained the critical communications to Australia from the war zone. 

Footnote

The old School of Signals is now the Defence School of Signals at Simpson Barracks, Watsonia and that new building from the early 1970s has been demolished and replaced with a newer two storey building.  However, the HLPA has survived and is still used for training military riggers. ⁽³¹⁾   Maybe it's the last Australian Army communication equipment from the Vietnam war era still in military service!

Antenna Technical Details

Horizontal Log Periodic Antenna (LP-1001)

The HLPA was invented by John Dunlavy in 1952 while working for the United States Air Force, but he was not credited with it due to its "Secret" classification.  The log periodic is commonly used in many frequency bands ⁽³²⁾, where it is desired to invest in only a single antenna to cover transmissions over multiple bands.

 

RASigs used the United States Antenna Products, LPA model LP-1001 antenna that had a frequency range 4 to 30MHz.  The antenna had 19 elements (longest element was 82’ (25m)) mounted on a 73’ (22.25m) boom and the boom mounted on a single guyed tower 84’ (25.6m) with rotator.  Its net weight was 1560lbs (708.kg) with a wind loading capability (no Ice) of 120mph (193kph). ⁽³³⁾

Vertical Log Periodic Antenna

The 1703 Series antennas are designed to provide transmitting and receiving service for HF circuits from 750 to 4000 miles.  Antenna gain is concentrated at best elevation angles for circuits of this length, and the angle remains virtually the same regardless of frequency.  The 4-32 MHz range of the antenna encompasses all frequencies required on most long-haul circuits. ⁽³⁴⁾

Notes:

1.   127 Sig Sqn never appear on the Order of battle for AFV.  When unit members were required, they were detached to either an in-country signals unit or AFV.  However, to honour their critical in-country support for RASigs, the unit was added to the RASigs Vietnam Plaque at the Australian War Memorial, dedicated on the 19 August 2008.
2.    See AFV War Diary AWM98-R723-1-13 Page 223.
3.    For more details see Pronto in South Vietnam 1962-1972, Chapter 6 at http://pronto.au104.org/index.html
4.    See 110 Sig Sqn War Diary AWM 6/3/6 (October 1967. Page 40).
5.   E513.  General purpose self-contained HF transmitter, 4 to 30MHz, 5kW output.  Data from RASigs Reference Manual 1969.
6.   See 110 Sig Sqn War Diary AWM 6/3/7 (November 1967).
7.   See AFV War Diary AWM98-R723-1-13 Vol 4 Page 119 (1968).
8.   HMAS Jeparit was an Australian National Line (ANL) bulk carrier which was operated by the Royal Australian Navy (RAN) between 1969 and 1972. She was launched in 1964 and transported supplies to Australian military forces in South Vietnam between 1966 and 1972 under both civil and military ownership.
9.    See 110 Sig Sqn War Diary AWM 6/3/12 (April 1968).
10.  See 110 Sig Sqn War Diary AWM 6/3/15 (July 1968).
11.  See 110 Sig Sqn War Diary AWM 6/3/17 (September 1968).
12.  See 110 Sig Sqn War Diary AWM 6/3/18 (October 1968).
13.  See 110 Sig Sqn War Diary AWM 6/3/15 (July 1968 – Monthly Report Works).
14.  See 110 Sig Sqn War Diary AWM 6/3/16 (August 1968).
15.  Details from Denis Hare (story author), the then 104 Sig Sqn draughtsman who remembers being tasked to attend the scene of the mine detonation and produce a map for the investigation.  Research for this story located that Private Michael Sukmanowsky, 1st Australian Reinforcement Unit was accidentally killed at Nui Dat on the 21 September 1968 by a claymore mine accidentally detonated.   Michael was a National Serviceman, aged 21 and had only been in-country two weeks.
16.  See 110 Sig Sqn War Diary AWM 6/3/34 (April 1970).
17.  See 110 Sig Sqn War Diary AWM 6/3/42 (December 1970).
18.  See 110 Sig Sqn War Diary AWM 6/3/43 (January 1971).
19.  See 110 Sig Sqn War Diary AWM 6/3/44 (February 1971).
20.  See 110 Sig Sqn War Diary AWM 6/3/45 (March 1971).
21.  See 110 Sig Sqn War Diary AWM 6/3/23 (February 1969).
22.  See 110 Sig Sqn War Diary AWM 6/3/47 (May 1971).
23.  See 110 Sig Sqn War Diary AWM 6/3/49 (July1971).
24.  See 110 Sig Sqn War Diary AWM 6/3/50 (August 1971).
25.  See 110 Sig Sqn War Diary AWM 6/3/51 (September 1971).
26.  See 110 Sig Sqn War Diary AWM 6/3/52 (October 1971).
27.  See 110 Sig Sqn War Diary AWM 6/3/53 (November 1971).
28.  See 110 Sig Sqn War Diary AWM 6/3/54 (December 1971).
29.  See 110 Sig Sqn War Diary AWM 6/3/55 (January 1972).
30.  Email details and photos from Trevor Hung and Robert Coventry.  Both 110 Sig Sqn war veterans from South Vietnam.
31.  Comments from. RASigs Facebook Site (October 2023).
32. One large application for LPAs is in rooftop terrestrial television antennas, since they must have large bandwidth to cover the wide television bands of roughly 54–88 and 174–216 MHz in the VHF and 470–890 MHz in the UHF while also having high gain for adequate fringe reception. One widely used design for television reception combined a Yagi for UHF reception in front of a larger LPDA for VHF.  See Wikipedia “Log-periodic antenna” at: https://en.wikipedia.org/wiki/Log-periodic_antenna
33.  HLPA Model LP-1001 data from RASigs Reference Manual 1969 and United States Antenna Products brochure.
34.  VLPA Model used details has not been recorded/located but was a single mast antenna array similar to the Kratos Defense & Security Solutions Inc 1703 Series detail at:  https://www.kratosdefense.com/-/media/k/pdf/s/a/1703-hf-antenna.pdf.

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