RC-292 Antenna

NSN 5985-00-497-8554
© Brooke Clarke 2004

The RC-292 is a VHF Low Band 1/4 wave vertical antenna with ground plane.  RC stands for Radio Component and this antenna was the successor to the RC-291.

The vertical and ground plane elements are made up of AB-21 series elements in the stock configuration or could also use MS-116 series screw together antenna elements.  The antenna only covers a small percentage bandwidth so different numbers of elements are needed to match a given frequency in the 30 to 88 MHz range used by Squad Radios.  Because of this bandwidth limitation the RC-292 can not be used with frequency hopping radios, like the SINCGARS, and so the OE-254 was developed.

This antenna is very reliable and has low loss when the correct number of elements are used for the desired frequency of operation.  Getting the RC-292 on top of a 30 foot mast adds a great deal of range when compared to a vehicle mounted antenna, like the AS-1729.

The OE-254 uses the MS-116 series antenna elements which have the same mating threads as the AB-21 series elements used on the stock RC-292.  These have copper as the exposed metal and when joined the copper oxidizes locking the elements together.  The male threads should be polished and a light coat of Radio Shack Lube Gel applied prior to assembly.

The RC-292 came out about the time of the PRC-8, PRC-9 and PRC-10 radios.  The three different element configurations of the RC-292 match the coverage of the three radios. 

Although mostly used for VHF low band it can be used as an HF antenna by using as many vertical antenna elements are you're comfortable with and adding wires to act as the counterpoise.

Table of VHF Low Band Radios

Radio	Frequency MHz	No of Vert Elements/ Length	Vert Elements	No. of ea. Gnd radial*/ Length	Gnd Elements	Opt MHz°
PRC-8 RT-66	20 - 27.9	6 120"	3 ea. AB-21 + 1 ea. AB-22, -23, -24	6 120"	3 ea. AB-21 + 1 ea. AB-22, -23, -24	31
PRC-9 RT-67	27 - 38.9	4 80"	AB-21, -22, -23, -24	5 100"	2 ea. AB-21 + 1 ea. AB-22, -23, -24	40
PRC-10 RC-68	36 - 54.9	3 60"	AB-21, -22, -23	4 80"	AB-21, -22, -23, -24	54
RT-246 RT-524 PRC-25 PRC-68 Fam PRC-77 RT-246 RT-524 PRC-6725(LB)	30.0 - 36.5	4 80"	AB-21, -22, -23, -24	5 100"	2 ea. AB-21 + 1 ea. AB-22, -23, -24
	36.5 - 50.5	3 60"	AB-22, -23, -24	4 80"	AB-21, -22, -23, -24
	50.5 - 75.95	2 40"	AB-22, -24	3 60"	AB-22, -23, -24

* multiply by 3 for the total number of elements
° Frequency of best match as determined by David Fiedler and are recommended operational frequencies to get the best performance out of the RC-292 in it's 3 stock configurations.  Other frequencies might be had by mixing and matching AB-2x and MS-11x elements, see below.

26 June 2004 - The AB-2x series of elements are 27" long whereas the MS-11x series are 1 meter long, otherwise they are interchangeable.

MP-68 Base

Note that the male threads and associated bare copper, about 3.5" long goes inside either the base or another antenna element, so for calculating the electrical length of some combination of elements you need to use the electrical length, not the overall length.

AB-21 Element is 23.5" over all length, 20" remains after screwing into another antenna element or a base such as the AB-15 or MP-68.

MS-116-A for comparison.  39.625" (1 meter) O.A. length, 36.25" remain after screwing into another antenna element or a base such as the AB-15 or MP-6.

Table of AB- and MS- Elements

male O.D.	female I.D.	Name	O.A. Len	El Len		Name	O.A. Len	El Len
0.337"	0.340"	AB-21	23.5"	20"		MS-116	39.625"	36.25"
0.335	0.220'	AB-22	23.5"	20"		MS-117	39.625"	36.25"
0.215"	0.220	AB-23	23.5"	20"		MS-118	39.625"	36.25"
0.215	ball	AB-24	23.5"	20"		MS-119	39.625"	36.25"

In an antenna made up of these elements there can only be one tip section (AB-24 or MS-119) and there can only be one reducing section (AB-22 or MS-117).  There can be a number of the base sections (AB-21 or MS-116) or a number of the smaller diameter sections (AB-23 or MS-118). 

For some reason most configurations only make use of a single AB-23 section, but the antenna may have better wind survival if a second AB-23 was used instead of the AB-21.  The resulting antenna would have lower wind resistance and be more flexible.

The MS-116 series elements can be used with the AB-21 elements to provide a much wider variation in electrical lengths.

The AB-24 can be stored inside the AB-21 just as the MS-118 can be stored inside the MS-116.  Doing this both saves space and protects the thinnest of the elements.

Table of Combinations of elements might be:

Length"	# AB	# MS	Opt Freq based on Vert len MHz = 3216 / in.
20	1	0	160
36.25	0	1	88.7
40	2	0	80.4
56.25	1	1	57.2
60	3	0	53.6 (54 MHZ*)
72.5	0	2	44.4
76.25	2	1	42.2
80	4	0	40.2 (40 MHz*)
92.5	1	2	34.8
96.25	3	1	33.4
100	5	0	32.2
108.75	0	3	29.6
112.5	2	2	28.6
116.25	4	1	27.7
120	6	0	26.8 (31 MHZ*)
128.75	1	3	25.0
132.5	3	2	24.3
136.25	5	1	23.6
140	7	0	23.0
145	0	4	22.2
148.75	2	3	21.6
152.5	4	2	21.0
156.25	6	1	20.6
160	8	0	20.1
165	1	4	19.5

* The 3 frequencies shown are where the VSWR of a stock RC-292 is optimum according to Proper use of the RC-292 antenna and are different from the classical ham radio (MHz =234/feet) calcualtions, probably becasue of the skew of the counterpoise elements of the RC-292.  For the two cases where the stock RC-292 uses counterpoise element lengths that are longer than the vertical length the equation is close to:
Optimum Frequency = 267 / feet = 3216 / inches.  ideally the counterpoise element length should be a few percent longer than the vertical, but can be the same length.

There may be some practical maximum number of elements or maximum length so not every combination is possible.
It may be that 3 different lengths of counterpoise elements may imoprove the bandwidth of the single vertical element.

RC-292 and OE-254 characteristics, problems -
Proper use of the RC-292 antenna - use the 3 minimum VSWR frequencies for best efficiency  (or choose element length to match frequency)