It is also necessary in waveguide slotted lines to place the slot at a position where the slot measurement in the waveguide walls is parallel to the slot. For accuracy, it is important that the probe disturbs the field as little as possible. However, these instruments are expensive and a common meter used in measurements with a slotted line is instead a cheaper low-frequency VSWR meter.
Figure 2 has a slightly different arrangement; the main probe into the waveguide leads to a vertical co-axial tuning and adjustment section but the detector is on a horizontal side-section with a secondary probe into the upright co-axial section.
So how does one accurately measure the dovetail width? This is followed by a section of waveguide 2 providing a transition to a smaller size of guide. The magnitude of the reflection coeffient can be calculated from the VSWR measurement by.
The two critical specifications of dovetail cutters are the width and the shoulder angle.
The carriage can be moved along the slotted line by means of a rotary knob 11 which simultaneously moves a vernier gauge 12 for accurate measurement of the probes position along the line. Although all the dovetails I've measured and worked with had 60 degree shoulders, a cast will help to confirm the correct angle.
Another method is to make a cast of the female dovetail slot using either Cerrosafe or epoxy. They are also tapered. I have not used this method but understand it works well as long as the Cerrosafe is removed at the proper time prior to enlarging slot measurement locking itself into the slot. In particular, they can only carry out a measurement at one spot frequency at a time so producing a plot of a parameter versus frequency is very time consuming.
An important component in the setup is the isolator 3 which prevents power being reflected back into the source.
In a co-axial slotted line, slot measurement slot is cut into the outer conductor of the line. The distance between the pins is measured with a vernier caliper and used in the formulas below. Due to the slight offset and edge thickness of the jaws, an accurate measurement is almost impossible.
The second part of the disturbance is due to energy stored in the field around the probe and manifests as a lumped equivalent of a capacitor. The current will then not be disturbed by the presence of the slot as long as it is not too wide.
A brass punch will work but will likely leave a thin brass smudge on the sight surface.
The most accurate technique is to use a couple of precision steel pins of identical diameters, which are placed in the dovetail refer to the figure below. One quick technique that works that works for me is to utilize a slightly tapered gauge, cut with common scissors out of thin shim stock.
If an existing front sight is being replaced the first thought may be, why not just measure the width of the base of the old sight with a conventional micrometer or vernier caliper? Once the cast is removed, measuring the width of the male dovetail cast is simple.
If an epoxy cast slot measurement made, it should be relatively easy to remove as long as the dovetail is sufficiently coated with a release agent such as paste wax. Sharpen the long edges of the gauge with a file or sandpaper. However, slotted line measurement techniques are more labour-intensive and often do not directly output the desired parameter; some calculation or plotting is frequently required.
The result is an equivalent circuit of a high impedance in shunt across the line which has little effect on the transmitted power in the line. The gauge is pushed in by hand and "wedged" into the bottom of the female dovetail until it stops.
There are two parts to this disturbance. There is no need for a DUT, better results are obtained with the reference short in position. If the slot is not tapered it was likely cut with a standard dovetail cutter. Therefore, be sure to follow the industry standard process of removing an existing sight by drifting it out from left to right and installing it from right to left.
The slot may be tapered at its ends to avoid discontinuities causing reflections. Standing wave patterns on a line for various reflection coefficients showing maxima and minima When the slotted line is terminated with a precision matching load there is no variation in the detected power along the line, other than a very small decrease due to losses in the line.
For this reason the probe diameter and slot width are kept small usually around 1 mm and the probe is inserted in no further than necessary. Just ensure the diameters of the pins are small enough to contact the side of the dovetails below the top edge.
Some of these parameters require the measurement of the exact position of the extremum. The shoulders are angled inward and the slot is cut to a specific depth. A test setup using a waveguide slotted line Figure 3.
The microwave power source is amplitude modulated with, typically, a 1 kHz signal which is recovered by the envelope detector in the probe and sent to the VSWR meter. The probe is more sensitive as a result of this tuning and the distance it is inserted can be further limited as a result. I found the right opening width was 0.
Lumped inductors are not practical at microwave frequencies; instead, an adjustable stub with an inductive equivalent circuit is used to "tune out" the probe capacitance. The width of a female dovetail slot is measured along the long axis of the barrel at the bottom of the slot, the widest fore and aft point of the dovetail.
In general it is slot measurement complex number. Their remaining uses are mostly in the millimetre bandwhere modern test apparatus is either prohibitively expensive or not available at all, and with academic laboratories and hobbyists. If you expect to be cutting numerous dovetail slots and installing sights, one solution is to order a wire gauge dovetail measuring tool from Brownells.
One other measurement that might be needed is the height or depth of the slot, which is easy to measure with a depth micrometer or the back end of a vernier caliper.