NOTES: The following has NOT been tested, and Jimbonzzz in a subsequent post brings up some issues which I didn't think of. The following information is for informational purposes only and is provided "as is" and without warranty of any kind. No warranty, either expressed or implied, shall be construed from the following information. Any modification to your radar detector may affect its operation, may affect your right to operate right to operate your radar detector as provided under Part 15 of the FCC rules, and may void your radar detector's warranty. Also note that you must take precautions against static electricity whenever opening or handling the electronics within any radar detector. Fortunately, you can simply remove the STi's bottom cover (#9 Torx screws), pull out the plastic window in front of the horns, and then reattach the bottom cover so that only the front of the STi's horns are exposed while installing any of these modifications.
This post is in response to Navalert who asked me if there is a way to inherently reduce the STi's X band sensitivity without having to use either the City mode or the City NoX modes, since these city modes progressively reduce K band sensitivity as well.
Navalert asked me if there are any simple methods to inherently reduce the STi's X band sensitivity without affecting the STi's K and Ka band sensitivities in any way. The STi, due to its stealth technology design requirements, uses a separate radar horn for detecting X band radar. It is the horn which is adjacent to the STi's RJ-11 power jack. I have had a few days to think about Navalert's request, and I have dreamed up three methods to achieve this goal.
One could, of course, put some Eccosorb radar absorbing foam either in front of the horn or inside the horn, but Eccosorb should be grounded using a special adhesive in order to perform properly and consistently if it is in contact with metal. The horn is metal and the Eccosorb adhesive is very strong. I wanted to create some simple solutions which could be installed just inside and at the very front of the X band horn using a couple of tiny dabs of contact cement, and which could be quickly removed if the STi should ever need servicing by Bel. So, here they are! I will describe the three solutions or methods further below.
The red shields described and shown can easily be cut out from thin sheet aluminum or thin sheet brass, and can easily be installed using small dabs of contact cement.
This method has the advantage of moderately reducing the STi's X band sensitivity and even further reducing the STi's off-axis X band sensitivity.
The solution is to contact cement two flat metal strips (shown in red) just inside and across the front of the X band horn. The horn is 1.1 inches (28mm) in width, which is the wavelength of X band. We want to reduce the horn's width to 0.5 inches (12mm) which is the wavelength of K band. This should reduce the STi's X band sensitivity by about 3dBm. The horn's width minus the K band wavelength (28mm - 12mm) equals 16mm. Thus each rectangular shutter should be 8mm wide. Since we will be mounting these rectangular shutters just inside the tapered horn, we need to reduce the width of each of these shutters to 7mm wide in order to still get an approximate 12mm wide central aperture within the front of the horn.
Off-axis X band sensitivity is further reduced since off-axis X band radar can only enter the horn through the reduced central aperture. The result is increased interaction of the radar reflecting off of the tapered vertical walls within the horn and the wave guide, resulting is additional off-axis phase cancellation once the radar reaches the LNA located deep within the horn. This works remarkably well for even further reducing alerts to X band door openers located along the sides of the road which are 25 degrees or more off-axis relative to the STi's horn.
This method is the simplest method for those who wish to greatly reduce or experiment in reducing the STi's X band sensitivity, since the reduction in X band sensitivity will be a function of the vertical height of the created entrance slit versus the 1/2" original height of the front of the horn. The implementation of this method should be obvious in the drawing.
The advantage of this method is that both the STi's on-axis and off-axis X band sensitivities are reduced by the same amount, that amount being whatever amount you desire based on height of the new entrance aperture versus the original height of the horn. For example, if you want to reduce the STi's X band sensitivity by 6dBm (a four times reduction in sensitivity), then the new entrance aperture should be 1/8" tall compared to the 1/2" height of the STi's horn.
This method, from an engineering standpoint, is the most pleasing since it involves making a new "floor" for the horn. It initially involves cutting a piece of paper to match the taper of the radar horn, and then bending the end of the paper at the front of the horn to create a front wall. The paper's edges are then traced onto a thin piece of sheet metal which is cut out and bent and then installed in the horn as shown. This method creates a completely new "floor" for the radar horn and at the same time reduces the horn's vertical entrance aperture to whatever you desire. Don't create a new "floor" which reaches too far inside the radar horn because you do NOT want it to come in contact with the LNA (the small black IC chip deep inside the horn). Instead, be sure that the rear of the floor comes no closer than 1/4" to the LNA chip (just eyeball it). Also, it is not critical to get a perfect fit between the edges of the new "floor" and the side walls within the STi's horn. Gaps up to 1/8" don't really matter, but try to shoot for gaps of about 1/16" since the smaller gaps will make it easier to contact cement the new "floor" in place. This is the reason for initially cutting out a paper template.
I will get around to creating PDF templates for all of these methods which you can print out. I will include templates to achieve different sensitivity reductions with each method.