1999 introduces an expanded line of XR series antennas. Last year was the first "XR" series antenna, the C-31XR, named after Natan, W6XR/2 (Force 12, East), who politely pushed for its completion. The C-31XR 31' boom no-trap tribander has become the antenna of choice for those who want the best. The basic design goals have been carried throughout the entire line that includes the C-19XR, C-31XR, C-36XR and C-51XR.

The XR series utilizes an overlaid Yagi technique for 20-15-10 mtrs. This is an extension of the Force 12 designs that have been in production for several years, such as the C-3, C-3S, C-3SS, 5BA, 4BA, 15/10 duobanders and the C-3XL. Besides utilizing the experience and knowledge of our successful designs, some of the groundwork was based on additional testing using models at 2-6GHz. The XR tribanders use three monoband Yagis that are placed onto the same boom, one on top of the other. This must be done carefully; otherwise, the antenna will not perform properly. One key is the right design that will pass energy through elements that are otherwise "unfriendly." Another key is the feed system. The three-band open sleeve developed by Force 12 for the C-3 and C-3S was modified for more flexibility. The XR triband feed is a combination of both the open sleeve and the "closed sleeve" (used on the C-3SS).

Design features on the XR series include:

• No traps for the highest efficiency (no need to estimate trap losses)
• High forward gain and excellent Front to Rear (front to side and F/B)
• Stepped gain on 10 mtrs to assist in stacking
• Low profile, riveted elements and tapered booms
• Standard 100 mph design (120 mph optional), with standard booms rated for >150mph
• Minimal mast torque
• Open space at the centre for side mounting
• 5KW+ rating (no traps to be concerned about)

Force 12, Inc. logically expanded the XR line for 1999 to meet the needs and dreams of more amateurs. A challenge was to add a 2el 40 Yagi to the tribander(s) without disturbing the excellent performance. The overlaid Yagi design on 20-15-10 does not allow "dropping" 40 mtr elements into the antenna. The most effective method is to add the 40 mtr Yagi in an area that does not impact the tribander, which is behind the reflectors. This adds to the boom length, but the results are what was desired: excellent quad-band performance on a single boom Yagi.

This is a great tribander that can be installed by everyone. The C-19XR shares the C-31XR technology in a smaller footprint. The 19' boom contains three overlaid monoband Yagis: 3 elements on 20 meters, 3 elements on 15 meters and 5 elements on 10 meters, with a single feed line. The patterns are excellent, as are the forward gain figures. Simple assembly, open area at the centre, 100 mph standard, with an overbuilt boom. It is designed specifically for optimum performance on 20-15-10 meters, 11 elements.

C-31XR

This magnificent tribander is the product of about 2 years development to provide an antenna that exceeded the C-3. It is the first to be released in the XR series. The C-31 XR is composed of three overlaid monobanders: for 20 mtrs, there is a wide-spaced 3 element; on 15, it has a wide spaced 4 element; and, on 10 mtrs, there are 7 elements, for a total of 14. The feed system is a new development by FORCE 12, utilizing both open sleeve and closed sleeve systems. It can be used as a single feed line and be changed in the field to separate feed lines to make maximum use of the new transceivers and for multi-operator contesting (remember to use band pass filters!). 120 mph optional, with no increase in wind load. 

C-36XR

The first of the quad-banders, the C-36XR is on a 36' boom. Using the C-19XR for 20-15-10, the 2el 40 mtr Yagi is placed to the rear of the 20 mtr reflector. The pattern on the close-spaced 40 is excellent and the operating bandwidth is about 130 kHz, with an optional relay box to switch between CW and phone. This relay box is the same as used on the 80 mtr dipoles and Yagis. The C-36XR is rated for 100 mph, optional at 120. 

C-49XR

The most powerful triple-monobander of all time! 49' boom, 24 elements! Force 12, Inc. announces the largest, highest gain triple-monobander: the fabulous, 49' boom, 24 element C-49XR. This is the "Big Daddy" to the 31' C-31XR that has rapidly become the triple-monobander of choice, out performing all other "tribanders."

More information about the new C-49XR can be found at:

This is the largest quad-bander ever built. The 51' boom has the entire C-31XR for 20-15-10, plus a 2el 40 mtr Yagi installed behind the 20 mtr reflector. This antenna is crated, having 20' of 4" boom at the centre, tapering down to the ends. It comes with the Force 12 drop-in tilt cradle mount for easier installation. The 2el 40 has the optional relay boxes available to work both modes. The 20-15-10 can use a single feed line, or separates, just like the C-31XR. The C-51XR is built in standard form for 120 mph. The first two C-51XR's are being installed in a stack with a C-31XR at VE1JF, for what he calls, "Excessive Force 12!" See 

C-19XR (11 elements, one 50 ohm feed line)

Boom Length	Wind Load	Freq. in MHz	Gain @74'	Net Gain	F/B Ratio	VSWR (max)	Turning Radius	Wt.	Mast Torque
19'	9.1	14.000-14.350	13.3dBi	5.2dBd	23	<1.6:1	20.3'	58#	<150 in/lb
		21.000-21.450	13.1	5.0	24	<1.8:1
		28.000-29.300	14.1	5.9	20	<1.4:1 (28.0-29.1)
Additional Data:		100mph rating. 21-inch open space at center

C-31XR (14 elements, 1, 2 or 3 Feed lines)

Boom Length	Wind Load	Freq. in MHz	Gain @74'	Net Gain	F/B Ratio	VSWR (max)	Turning Radius	Wt.	Mast Torque
31'	10.7	14.000-14.350	14.0dBi	6.0dBd	20	<1.7:1	23.8'	82#	<200in/lb
		21.000-21.450	14.3	6.3	22	<1.7:1
		28.000-29.300	15.6	7.4	21	<1.7:1 (28.0-29.1)
Additional Data:		100mph rating, 120mph optional. 30-inch open space at centre

C-36XR (13 elements, 2 Feed lines)

Boom Length	Wind Load	Freq. in MHz	Gain @74'	Net Gain	F/B Ratio	VSWR (max)	Turning Radius	Wt.	Mast Torque
36'	13.8	7.000-7.300	12.1dBi	4.0dBd	20dB pk	2:1 (adj., 130 kHz)	29.2'	108#	<120 in/lb
		14.000-14.350	13.3	5.2	23	<1.6:1
		21.000-21.450	13.1	5.0	24	<1.8:1
		28.000-29.300	14.1	5.9	20	<1.8:1 (28.0-29.1)
Additional Data:		100mph rating. 30-inch open space at center. 40mtr adjustable in band.

C-51XR (15 elements, 1 feed line for 40, 1-3 feed lines for 10/15/20)

Boom Length	Wind Load	Freq. in MHz	Gain @74'	Net Gain	F/B Ratio	VSWR (max)	Turning Radius	Wt.	Mast Torque
51'	15.5	7.000-7.300	12.1dBi	4.0dBd	20dB pk	2:1 (adj., 130 kHz)	34.2'	173#	<800 in/lb
		14.000-14.350	14.0	6.0	20	<1.7:1
		21.000-21.450	14.3	6.3	22	<1.7:1
		28.000-29.300	15.6	7.4	21	<1.7:1 (28.0-29.1)
Additional Data:		120mph rating. 70-inch open space at centre. 40mtr adjustable in band.

Gain at 74'
Gain is achieved by redistributing the available energy into a preferred direction at the expense of other directions. It is usually measured at the point of most energy in the preferred lobe of an antenna. Gain is expressed in a relative term, "dB something", where "something" is the important reference (what it is compared to). Horizontal antennas are specified in two ways:

• GAIN @ 74' is given in dBi at the computed gain of the antenna at a height of 74' (over average, real ground), as compared to the theoretical isotropic source (reference). This dBi figure will be familiar to those who do computer modelling and is numerically much larger than the "apples to apples" dBd comparison, by roughly 7-7.5dB. This comes from two places. One is from the difference between the theoretical isotropic source in free space to a dipole in free space, which accounts for 2.14dB (the pattern is changed from a sphere in free space to a figure 8 above ground, which indicates how the energy is redistributed). The second is from "ground reflection gain," which is the enhancement for a horizontal antenna installed above real ground, due to the effect of the ground. Values for ground reflection gain on horizontal antennas depend on the height in wavelengths above ground and average 4.5-5.8dB. If 2.14 (isotropic source) and 5.9 (maximum ground reflection gain) are subtracted from the dBi figure, one will arrive at approximately the dBd "apples to apples" number.

  NET GAIN is given in dBd as compared to the full size, resonant reference dipole at the same height, in the same location. This is the "apples to apples" comparison and is labelled, "NET GAIN."

• F/B ratio is the peak (minimum) difference between the forward and reward pattern. A high F/B at a single point (180 degrees to the rear) does not necessarily means the antenna has good rejection to the sides and rear quadrants (F/R). FORCE 12 antennas have excellent F/R.

  VSWR is the highest value (usually at the band edges) for a typical installation through an RF choke or 1:1 balun. Within the band, the VSWR will usually approach 1:1. The actual VSWR measured might be lower than these values, because coax has a small amount of loss and this acts to smooth out the VSWR curve. If the frequency of the lowest VSWR shifts with a change in coax length, the balun or RF choke is not effective. Proximity to other antennas or other objects (i.e. roof and ground), can change these values.

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