OE-254/GRC Antenna Group

Brooke Clarke 2000 - 2014

OE-254 VHF low band
          antenna

OE-254 by N6GCE


1.0 Background
2.0 Preparation for Use and Installation
3.0 Operation
4.0 na
5.0 Maintenance Instructions
6.0 Parts List
7.0 Reference Information
8.0 Experiments
9.0 Related
10.0 Links

1.0 Background

The OE-254/GRC is a biconical antenna that uses a Balun (BALanced to UNbalanced transformer) to match the 50 Ohm coax line and radio to the 200 Ohm antenna.  It covers the 30 to 88 MHz frequency range without any element adjustments and therefore is said to have an instantaneous bandwidth.
The RC-292 antenna needs to have three different element lengths to cover the 30 to 88 MHz frequency range and therefore is not suitable for use with frequency hopping radios.
The OE-254 was designed for frequency hopping and conventional radios.  You also do not need to be lowering and rasing the antenna to work anywhere in the 30 to 88 MHz band.

I suspect that this bi-conical has a much wider bandwidth than the specification, just as a diskcone has a wide bandwidth.

Note that the AS-1729 and AS-3900 VHF Low band vehicular antennas have about MINUS 6 dB gain relative to a dipole.  These would not be suitable for use with the squad radios 1 Watt output power.

Antenna elevation is very important in this frequency band.  Placing the OE-254 on all the mast sections makes a huge difference in it's coverage area.  There are some web references to a new wide band antenna that's compact and light weight and is deployed on the ground, i.e. it does not use a mast.  This no matter how well matched this antenna is, it never will have the coverage of the OE-254 up on a mast.

These antennas don't seem to be current as of 2008.  The Harris RF-9072 Low-Band VHF Discone Antenna may be a replacement.
The Create Discone may also be a replacement.

1.1 Photos

Mast Sections - (Fair Radio photo) look like they have tabs and notches
Stakes, guy ropes, etc. -(Fair Radio photo)
Feedcone Assembly - Red Label:  "CAUTION Always use the 30 Inch Insulating Mast Section With This Antenna"  The thread in the bottom cone is a little different from the thread used on a broom handle, but it's close.   The feedcone consists of a 50 Ohm to 200 Ohm balun transformer driving the upper cone that's all metal and the lower cone that's all metal 180 degrees out of phase with each other.  The DC resistance between all the parts is less than 0.1 Ohms.  Even with a 4-wire Kelvin Ohm meter I could not see the balun windings.  This is probably because the wire used on the balun is big enough to handle 350 Watts of RF power and has a very low DC resistance.
CG-1889C/U Coax Cable Assembly -
Antenna installed on the Lower mast sections (1/2 normal height) -
There are 3 antennas in this photo including the OE-254
  - See PRC-126/OF-185 Drive Testing for more info
18 March 2001 -
OE-254 using all the mast sections
(twice as high as before)
OE-254 VHF Low
                  Band Antenna full height






1.2 Problems

All of these problems have solutions and are no reason to not use this antenna.  All antennas have similar, if the the exact same, problems that need to be addressed.

Safety

The original version must have just used the AB-24 Mast Sections with no end tip and people died and/or were blinded by being impaled.  The teardrop shaped tips that are now on the tips of all military antennas are not there to increase the reception of distant stations, but are purely a safety measure.

Staking in Soft Ground

If the antenna is erected on soft ground (or sand) the strength of the stakes may not be enough to hold the antenna up when the wind blows.  To improve the strength of the staking use two stakes for each guy rope for a total of 16 stakes.  This requires adding a pair of stakes at 45 degree intervals rather than only at 90 degree intervals around the mast.  The manual shows 4 stakes holding 2 guy ropes each for hard ground.

Feedcone Separation

The upper and lower cones are Aluminum castings that are glued to a center insulator.  It's possible for the glued joint to crack.  See the PS magazine articles for instructions on using cord (NOT WIRE) to tie the cones together.  I have an idea how to really fix this problem, but need to try it out.

Strain Relief Failure

The Strain Clamp PF-211/G may have too smooth an inner surface and let the coax cable slip.  If this happens the coax probably will break free of the connector and the electrical performance will be ruined.  The manual and the PS magazine articles recommend using electrical tape to attach the coax to the mast.  And to rough up the inner surface of the Clamp.

Corrosion

Wherever there is an electrical connection between the cones and between antenna elements there is the possibility of corrosion.  In the feedcone that I just received there is corrosion in the element sockets.  These need to be cleaned with a small arms cleaning brush and I need to find an anticorrosion compound at my local hardware store.

My antenna was put up without any preventive measures and after a couple of months the antenna elements had locked to each other.  Large pliers would not undue the joints.  The cause was the copper oxidizing.  Compare a polished and corroded MS-117A end.  You can see that both Silicon Grease and COAX-SEAL are needed at every joint.  The reason for adding the COAX-SEAL is that water is the universal solvent.  Given time and weather I am concerned that the Silicon Grease is not enough.

Weatherproofing

The manual shows in Figure 2-18, using electrical tape to weatherproof the joint between the coax cable and the feedcone.  There are two problems with this illustration.  (1) It is a very much better idea to use COAX-SEAL (Radio Shack: 278-1645) instead of electrical tape. (2) the COAX-SEAL should be applied all the way to the feedcone body, it should not stop at the back of the connector nut as shown in the figure.  After decades the COAX_SEAL can still be removed enough to disconnect the coax and it will look like new, it's really a great product!

I have just learned of another product and it's Silicon grease. Radio Shack: 64-2326 "Lube Gel".  My local auto parts store has "Dielectric Silicone Compound, for electronic ignitions" Napa p/n 765-1190, but it costs 4 times more.  This idea with these is that you squirt some into the cavity of the connector then mate the connectors.  The Silicon fills up the air space and prevents and water from getting into the joint.  The dielectric constantof the plastics used in connectors is around 2 or 3.  Water has a dielectric constant of about 60, which can cause a lot of problems.

Poor Design Type N Connectors

The type N connectors used on this cable are a poor design.  If torque is applied to the cable after the connector is mated it's possible to shear all the shield braid wires.  After this happens the connector does not readily come off the cable, but it's performance is ruined.  To test for this, with the connector disconnected, hold the back of the connector (near where it attaches to the cable) and turn it a few degrees.  If it rotates freely it's already bad.  If you pull a bad connector it will come completely off the cable.  For this reason it very important not to apply ANY torque to the cable once the connector is mated.  There are Type N connectors that are molded onto the cable that also incorporate torque, strain relief and weather protection. These would be much better in this application.  Of course with the existing connector, when it fails, the same connector can be reinstalled on the cable.

Broken Toroid

Maybe because of a hard mechanical shock or too much RF power the torrid may break.

Fig 1
OE-254
                  Bi-Conical VHF Low Band Antenna Feed Cone Inside
White to RF Type-Nf center
Black to RF Type-Nf ground
Cap: CM05ED-240J03 (Mica 24pF 500V 5%)
Toroid is ID 1.375 (1 3/8), OD 1.875 (1 7/8) and H .375 (3/8)
Fig 2
OE-254
                  Bi-Conical VHF Low Band Antenna Feed Cone Inside
Fig 3
OE-254
                  Bi-Conical VHF Low Band Antenna Feed Cone Inside

Fig 5
OE-254 Feed Cone
                  Broken Toroid


Fig 5 Items:

1. Good replacement assembly
2. FT140-43 from Kits and Parts
3. Unknown toroid.
4. Coax feed
5. Feed cone with broken toroid.
Fig 6 There is only one way to install the connector
cap because the bolt pattern is not symmetrical.
OE-254 Antenna
                  Feedcone



OE-254 Feed Cone Parts Location
OE-254 Antenna Feed Cone Schematic

Measured Impedance of transformers with cap.

1. Good replacement assembly
tested with existing 24 pf cap
OE-254 feedcone good transformer
2. FT140-43 from Kits and Parts
tested with 25 pf cap
OE-254 Transformer made from
                FT140-43
3. Unknown toroid. OE-254 feedcone with unknown
                toroid
5. Feed cone with broken toroid. OE-254 feedcone with broken &
                taped toroid
Conversion: Z:Transform
Network: R
After
CAL
Response
Short
Done
HP 4395A after Response cal with
                short in series.

Note:  The above data is based on small signal measurements.  When power is applied (say 25 Watts) then the core needs to keep working.  This is very different from small signal measurements.  That's to say the above measurements apply to receiving signals, but not transmitting.

One way to check how well a coil works is to make two of them and connect back to back.  Then drive a 50 Ohm load and see how hot they get and what the VSWR looks like.


2.0 Preparation for Use and Installation

2.1 Before You go into the Field

Your hands can get quite cold, so it's best to have every thing prepared before you start to set up the antenna.
Be sure that the guy ropes do not have a bunch of extra knots from the last installation (there is no need for extra knots).

2.2 In the Field

There are 4 guy ropes arranged at 90 degree intervals on a 25 foot radius (50 Foot diameter) circle.  Two of these are in line with the hinge that is used to tilt the mast up and down and the other two are at right angles.  This allows the guys at the sides to keep the mast lined up as it is raised or lowered.

There are blue (water on the ground) and red (hot sun) color coding on a number of the parts.  The blue parts are installed closest to the ground and the red parts are at the top.  It is possible to use only the blue parts for a shorter mast, and that's what I am now working on doing.  Easier to put up and down for testing some ideas.

Before doing anything with the feedcone, I titled up the mast by it's self and got the lengths of the 4 guy ropes correct.  This is very easy to do without the weight of the feedcone and elements.

A chair comes in very handy to hold up the mast while the feedcone is fitted.  I installed the insulating section on the feedcone and the top three elements. then after the feedcone was attached to the mast I installed the lower three elements.

There is a special mast section with a notch in one and and a red band painted on the other.  This section is used to connect to the Blue (big) lower sections and reduce the size for the Red upper sections.  It must be used in all installations, because a smaller diameter (Red) section must be there for the insulating section that holds the Feedcone.

Rather than use the Strain Relief PF-211/G, I used tie wraps to secure the coax to the mast.  This works much better and faster.  You can see the tie wrap tails in the photo above.

See Drive Testing for more information.

If you want to connect to coax cables toghther for a longer run you will need a type-N male to male barrell NSN 5935-01-035-5650.


3.0 Operation

3.1 Frequency Coverage

The 3.5:1 VSWR specified bandwidth is 30 to 88 MHz.
Testing using the Agilent 4395A Spectrum Analyzer shows it is better than the Radio Shack 20-176 over the 88 to 108 FM radio band.
Radio Shack 20-176 Antenna FM
                broadcast band Spectrum Plot Radio Shack 20-176 Scanner Ant Spectrum Display of FM Broadcast Band

This is a way to compare the OE-254 or Radio Shack antennas to see how well they work on the FM broadcast band.

The Radio shack is working in it's frequency range, but the OE-254 is working above it's range.  The OE-254 performs much worse that the Radio Shack in the FM band.  That indicates that the balun in the OE-254 is probably optimized for 30 to 90 MHz.
OE-254 Antenna Spectrum Plot FM
                Broadcast Band
OE-254 Antenna FM broadcast band Spectrum Plot

The OE-254 works fairly well as an FM antenna.
OE-254 Smith Chart 30 to 108 MHz
OE-254 Smith Chart 30 to 108 MHz

30 - 108 MHz, marker 0 @ 30, Mkr 1 @ 88, Main Marker at 51 (Z=63 -16j)
Note when evaluating a receiving antenna the spectrum plot is more important than the VSWR plot.  Even better is the signal quality vs. frequency plot you get from the chirp receiver, but that only covers the HF band.

In this case the OE-254 has a reasonable VSWR in the Fm broadcast band (88 to 108 MHz), but it does a poor job in that band receiving signals.

5.0 Maintenance Instructions

See the PS magazine articles below.

For some parts contact Steve Haney of  Haney Electronic Company.


6.0 Parts List

Complete OE-254/GRC Antenna

Description
NSN
Figure
Item
FSCM
Part No.
Qty
Antenna OE-254/GRC 
5985-01-063-1574
   
80063
SM-D-944750
1

Major OE-254/GRC Components

Description
NSN
Figure
Item
FSCM
Part No.
Qty
Extension, Insulating
5985-01-072-4342
C1
1
80063
SM-8-944747
1
Feedcone Assembly AS-3166/GRC
5985-01-074-6684
C1
2
80063
SM-D-944759

Mast Section AB-24/GR
5820-00-240-3720
C1
3
80063
SCD13614AB24GR
6
Mast Section MS-116A
5985-00-199-8831
C1
4
80063
SDI252IMS116A
6
Mast Section MS-117A
5985-00-115-7149
C1
5
80063
SCD1252IMS117A
6
Antenna Tip Assembly
5985-00-930-7223
C1
6
63904
SC-C-446046
6
Mast AS-1244/GRC
or
Mast AB-1244B/GRC 
     
80063

80058

SM-D-866154

 

1
Bag, Transit - Packing & Setup Instructions
5985-01-072-4339
C6
1
80063
SM-D-944752
1
Deleted  
C6
2
   
-
Connector, Adapter  TRU-2064  
C6
3
92180
 
1
Hammer Hand, 2 1/2  lb.  Type X, Class 1
5120-00-203-4656
C7
8
81348
GGG-H-86C
1
Running Spares  
C6
C7
4 - 7
9 - 12 , 14
   
Technical Manual: TM 31-5985-357-13
5985-00-930-7223
C7
13
   
1

Mast AS-1244/GRC

Description
NSN
Figure
Item
FSCM
Part No.
Qty
Adapter Assembly, Lower
5985-01-327-1448
C2
1
80063
A3159895
1
Adapter Assembly, Upper
5985-01-326-5533
C2
2
80063
A3159902
1
80 Ft. Cable Assembly, Radio Frequency CG-1889C/U
5995-01-085-1665
C2
3
80058
 
1
Clamp, Electrical Conductor, Strain Relief PF-211/G
5975-01-072-4496
C2
4
80063
SC-DL-14203
1
Guy Assembly
5985-01-072-4414
C2
5
80063
SC-D-659410-GP1
4
Guy Assembly 
5985-01-072-4415
C2
6
80063
SC-D-659410-GP2
4
Guy Plate 
4030-01-074-7881
C2
7
80063
SM-B-659290-1
1
Guy Plate
4030-01-072-8126
C2
8
80063
SM-B-659290-2
1
Mast and Base Assembly
5985-01-072-8018
C2
9
80063
SM-D-659263
1
Mast Section Assembly,  Lower
5985-01-324-3462
C2
10
80063
A3159892
5
Mast Section Assembly, Upper
5985-01-324-3463
C3
11
80063
A3159899
5
Base Plate
5985-01-122-3959
C3
12
80063
SM-6-659275
1
Stake, Base Plate
4030-01-072-8017
C3
13
80063
SC-B-729924
2
Stake Assembly, Guy
5985-01-073-6103
C3
14
80063
SM-C-65937
4

Mast AB-1244B/GRC

Description
NSN
Figure
Item
FSCM
Part No.
Qty
Adapter Assembly, Lower Blue
5985-01-327-1448
C4
1
80063
A3159895
1
Adapter Assembly, Upper Red
5985-01-326-5533 
C4
2
80063
A3159902
1
80 Ft. Cable Assembly, Radio Frequency CG-1889C/U
5995-01-085-1665
C4
3
80058
 
1
Clamp, Electrical Conductor, Strain Relief PF-211/G
5975-01-072-4496
C4
4
80063
SC-DL-14203
1
Guy Rope Assembly Blue
5985-01-072-4414
C4
5
80063
SM-D-659410-GP1
4
Guy Rope Assembly Red
5985-01-072-4415
C4
6
80063
SM-D-659410-GP2
4
Guy Plate Blue   1 11/16" I.D.
4030-01-074-7881
C4
7
80063
SM-8-659290-1
1
Guy Plate Red    1 1/2" I.D.
Pole Protector Red
4030-01-072-8126
4030-01-072-8126
C4
8
80063
2S308
SM-B-659290-2
1
Mast and Base Assembly
5985-01-324-3464
C4
9
80063
A3159890
1
Mast Section Assembly,  Lower  2' 7" functional len
5985-01-324-3462
C4
10
80063
A3159892
5
Mast Section Assembly, Upper   2' 3" functional len
5985-01-324-3463
C5
11
80063
A3159899
5
Base Plate
?
C4
12
80063
A3002872
1
Stake, Base Plate
4030-01-072-8017
C4
13
80063
SC-B-729924
2
Stake Assembly, Guy
5985-01-073-6103
C4
14
80063
SM-C-659375
4

7.0 Reference Information

    7.1 Manuals

TM 11-5985-357-13

    7.2 Web Links

FM 24-19 - -Section IV. Antenna Group OE-254/GRC -
FM 24-24 - Chapter 4 -
Steve Haney - antennas and other mil radio stuff
NSN List.pdf - by The Romad Locator -
Fair Radio - AB-1244/GRC Mast Kit - Used on the OE-254, RC-292 and OE-303 Antennas

PS magazine

2003
PS magazine Issue 604 March 2003 pages 44 & 45 "OE-254 Antenna Advice" is my article on the OE-254 that corrects the error in issue 560.
2002
    Maintain 'em to Stand Tall                                 596  42 - 45
2000
    Be a Rust Buster                                            582 (no correction for wire problem above)
    Double Staking in Loose Ground                     577   51

1999
            Subject               ______________      Vol    page
Antenna support sleeves                          560     52 Is It Modified?     
Feedcone assembly, elements, cables        560    48 -Before you raise'em....you better maintain'em - There is an error on the bottom of pg 49 it says "Try substituting wire for the cord.  The locking wire NSN 9505-293-4208, used in your arms room will work.
THIS IS WRONG, USING WIRE WILL SHORT OUT THE ANTENNA AND MAY BURN UP YOUR RADIO!!!!!!
1998
           OE-254, RC-292--Safety tips                   545     50
1997
        Mast section MWO                                   531     53
        Facing the Feedcone Facts                        536      36
1996
        Twisting the Rust Away - Feedcone cleaning      518     43
        The Feedcone That Couldn't Resist           529     45 - essentially a short everywhere because of the balun
        Staking Technique                                    525      48
1995
        Anenna Safety - A Tall Order                   506     46 - tip caps NSN 5985-00-930-7223 & electrical tape

1994
    Antenna PMs a Tall Order                              500       46 - 48
    Gone With The Wind                                       494      50-53 m It's OK to use insulating cord to hold the cone toghther.
    Get The Point                                                   504   47
1992
    Right Lube Means Clear Signal                     472   44, 45  Water Displacing Compound
1991
    Good PM Thaws Frostiest Antennas               468 40, 41
    Cable Adapter NSN                                       465   61
1990
    Antenna Peak Points         455      42, 43

8.0 Experiments

RF Currents on the Outside of the Coax

The existing design uses a 30" insulating mast section just below the feedcone, but still has the coax going down the mast.  The effect of the coax is to short out the vertical component of the lower antenna elements and that's the key radiating polarization.  It may be a good idea to place ferrites (RS 273-104 7/16"x7/8" or 273-105?) at the base of the feedcone and at the joint between the metal mast and insulating mast section to block any RF currents running on the outside of the coax.  The effect may show up in the impedance looking into the end of the coax or in signal strength.

New Feedcone Design

An improvement might be to design the center insulator to both be much stronger and also to have the option of mounting the biconical elements in a horizontal configuration.  This would change the polarization from vertical to horizontal and double the broadside gain and add two nulls off the sides.  It would be interesting to see the effect on range with the other radio running vertical and horizontal polarization.  By turning the feedcone 90 degrees to the horizontal position the uppermost mast section can now be metal because it would be orthogonal to the active antenna polarization.

9.0 Related

AS-2360 HF Loop Antenna Parts List
Antennas
Antenna Adapters for sale made by N6GCE
AS-1405/PRC-41 UHF Antenna
AS-1729/VRC VHF Vehicle Antenna that uses the MX-6707 Base , AS-1720/VRC & AT-1095/VRC Antenna elements
AS-2109 VHF low band VHF Antenna (simulates either the AT-271 or AT-892 on the PRC-77
AS-2259/GR HF NVIS Antenna and NVIS in General
AS-3588/GRC-206 VHF-AM & UHF-AM Antenna
AT-1011/U aka Shakespeare 120 HF Antenna - 16' or 32' whip
AT-271/PRC 10' Fishing Pole Antenna used on many radios both HF and VHF
AT-984/G Fishing Reel Antenna used for both HF and VHF
Eyring Low Profile HF Antenna 301A (ELPA 301A)
GRA-50 Antenna, HF NVIS Dipole w/reels at the ends
30 to 88 MHz VHF Low Band Antennas
AMRAD LF Active Whip Antenna
LST-5B UHF radio w/ D&M C152-1-1 SATCOM  Antenna
WWVB (6o kHz) Loopstick Antenna & C-Max Receiver
OE-254/GRC Antenna Group - this page
OE-303 1/2 Rhombic VHF Antenna
PRC-68 Family Antenna Adapter 68AA with DC return
RC-292 Antenna, VHF low band mast mounted & MS & AB mast elements & Batt Adapter for PRC-8, PRC-9 & PRC-10
SATCOM  Antenna UHF - Dorne & Margolin C152-1-1
Shortened Antennas for Portables by Dennis Starks
SORAK Special Operations Radio Antenna Kit OE-452/PRC Five Configurations HF through VHF coverage
Trivec-Avant AV 2095 UHF Satcom Antenna System - Gyroscope keeps vehicle mounted antenna pointed as satellite.
TRQ23 Radio Receiving Set AN/TRQ-23 Antenna Group OE-4/GR AS-2360 Series Loop Antennas
Wire Antennas - TCI651 HF Ant, mainly about Camouflage Netting Mast Kits, including antenna line launchers CSV17 Tennis ball and EZ-Hang Slingshot

10.0 Links

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page created 28 Dec. 2000.