California amplifier downconverter

The antenna is mounted at each subscriber location and directed towards the head end. To reduce added noise due to long signal paths, the downconverter is sometimes combined with the antenna. The antenna includes a plurality of separate director discs assembled in an axially spaced relationship on a rod which mounts to a backplane member defining a reflector and planar side lobe suppression ears.

A receive disc is spaced from the reflector and energy is coupled from the receive disc perimeter with a coaxial cable which is looped to the downconverter. A cup shaped dielectric member provides environmental protection for the receive disc. The combined antenna and downconverter is mounted to a mast with a clamp. Other related antenna structures are disclosed in U.

Preferred embodiments of the invention are characterized by a housing having transversely spaced arcuate ears extending from a first face, an integral director carried by the first face and comprised of a plurality of axially spaced discs including a terminal director disc located proximate to said first face, a receive structure proximate to said terminal director disc, and a plurality of circumferentially spaced mounting jaws formed on a housing second face with each configured to engage a support mast.

In accordance with an important feature of the preferred embodiment, each of the mounting jaws are located to align the receive structure with a selected one of the polarized microwave signals. They are preferably grouped in radially spaced pairs to more effectively grip the support mast. A stop is defined by the housing second face to locate a clamp thereon for enclosing the support mast with any of the jaws.

In a preferred embodiment, the receive structure includes a reflector cup formed on the housing first face and a receive disc carried therein. Downconverter electronics is preferably carried within the housing and coupled to the receive structure. The housing and director discs are preferably each configured as integral pieces for economical fabrication and assembly.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

I mounted to a vertically oriented mast 22 in the form of a cylindrical tube. The director 26 defines an antenna axis 32 and is supported by a nut 33 mounted on a first face of the housing assembly The director 26 is configured to provide high directivity while its slender profile reduces wind and ice loading compared to many alternative antenna configurations, e.

Arcuate side lobe suppression ears 38 are carried by the housing assembly 24 to reduce off-axis signals and increase on-axis gain. The housing assembly 24 includes a mounting jaw system 36 arranged to selectively physically orient the housing assembly on the mast 22 in alignment with the microwave signal polarization. The housing assembly 24 also provides stops to assist positioning the clamp 28 for each housing assembly orientation. A single coaxial drop cable 34 delivers the downconverted signal to receivers located below while its center conductor provides an upward path for DC voltage to power the downconverter electronics.

For example, the director 26 and main parts of the housing assembly 24 can be cast as integral pieces and installation of the downconverter electronics requires few steps other than a few soldering operations. A number of structural details of the embodiment 20 describe cylindrical paths about the axis 32 shown in FIG. Accordingly, the following description will make use of spatial adjectives axial, radial, and circumferential in referring to directions respectively along the axis 32, away from the axis 32 and circumferentially about the axis These views show the housing assembly 24 to include a housing 51 preferably formed of a body 52 and a cover The housing body 52 defines a reflector cup 54 having a back 56 and an annular rim The annular rim 58 is interrupted by radial drain slots 59 and defines an annular step 60 at the top edge of its inner side.

The housing body 52 has a transverse web 64 which separates the reflector cup 54 from a chamber This transverse web 64 defines, in the center of the reflector cup, a forward directed boss 67 which receives a threaded stud An insulated feedthrough 70 projects axially through the web 64 so that a first end 72 is available in the reflector cup 54 and a second end 74 is available in the chamber A receive disc 50 is preferably fabricated from a low loss material, e.

The receive disc 50 is mounted over the stud 68 with its indentation 78 receiving the feedthrough first end Thus the feedthrough first end 72 is positioned to receive energy from the voltages developed in the receive disc A fiat dielectric wafer 80 functions as a radome. The wafer has a center hole which receives the stud 68 while the perimeter 82 of the wafer is received into the annular step 60 formed in the periphery of the reflector cup The nut 33 is threaded onto the stud 68 to secure the receive disc 50, washers 84 and wafer 80 on the housing body Downconverter electronics are carried on a microstrip circuit board shown in FIGS.

The first and second ends 72, 74 of the feedthrough 70 are soldered respectively to the receive disc 50 and the microstrip board to effect a short, low loss path therebetween. The downconverter input impedance, e. Attention is now directed to details of the integral director 26 as shown in FIG. The director has a central rod which defines axially spaced director discs including and terminating in a terminal director disc A.

The end of the rod adjacent to the terminal director disc A is threaded to mate with the nut A stop abuts the nut 33 to set the spacing between the receive disc 50 and the terminal director disc A when the stud 68, nut 33 and director 26 are fully engaged as in FIG. Along the sides of the stop , the rod defines a pair of fiats to facilitate use of a tool, e. These views illustrate details of the jaw system 36 referred to above relative to FIG.

The integral housing cover 53 defines a pair of radially spaced arcuate bosses A, B. In FIG. The step intersections thus form ridges , and arranged to engage various sized masts. For illustrative purposes, the ridges , , are shown to abut a mast rotated 90 degrees from the mast 22 of FIGS.

The jaws , are diametrically opposed and, together, form a first jaw pair , aligned along the centerline In a similar way, the bosses A, B form a second jaw pair , aligned along the centerline and a third jaw pair , aligned along the centerline The centerlines and are respectively rotated 45 degrees and 90 degrees from the centerline The jaw pairs are thus circumferentially spaced 45 degrees and configured to receive the mast 22 to position the housing assembly 24 in a selected one of three circumferentially spaced relationships with the mast.

Therefore, as shown in FIG. The clamp 28 includes a yoke broken away for clarity of illustration in FIGS. The clamp 28 also includes a clamp screw that is threaded through the yoke to compressingly abut the mast Preferably, the imaginary line shown in FIGS.

Further amplification is applied at this point to overcome cable losses and to restore the overall performance. Figure 1 - Cal Amp block diagram. The PLL consists of four components.

The whole PLL system divides this by a total of to compare with the reference crystal. Therefore, to change the PLL frequency, we change the reference crystal. Unconverted the units do not have sufficient sensitivity to receive signals, except the strongest, gain being many dB's lower at and MHz than the MMDS portion. Retuning the filter, in the case of the satellite allocation at MHz is not unnecessarily complex, and the entire filter can be slabbed with a sheet of Teflon shim to bring the filter resonance back to MHz.

A piece of 0. This is the simplest modification possible, and is a compromise. With this modification further test equipment is desireable, as it is necessary then to provide a variable signal at the signal frequency, and a means to monitor that signal and peak up the filter for best response.

Using small pieces of copper or brass shim 0. These are individually tinned, and waved over the existing stripline until an improvement can be obtained, whereupon they are soldered in place, repeating the whole excercise until no further improvement can be obtained. Many tabs and a fair amount of time and skill is required to obtain the best results. Reference to the appendix included with this document is advised for this procedure - it is the author's preferred method.

Working ones way from the output side of the filter to that of the input is the method to adopt when retuning this filter. One usable scenario for retuning is illustrated in Figure 2 below. More sophisticated test equipment can of course be used instead. The basic idea is merely represented here, but the system outlined does produce good results.

Figure 2 - Retuning setup with basic equipment. Note that it is very important to not manually tune this filter for the highest S-meter reading, the mixing process produces not only the wanted signal, but an image signal which will be noise. Tuning for best S-meter reading will allow more of the unwanted 'noise' to interfere with the wanted signal.

Access to a SINAD meter is not so important if you have good ears, and can tell the difference in quieting. It is not necessary to adhere to this when 'cladding' the filter with PTFE, as you will have to accept the results obtained by this method. The author is very lucky to have good hearing, and can equal the results obtained with a SINAD meter. An oscilloscope connected to the receiver's output will aid manual retuning to some extent by examining the roughness of the modulation.

As was said earlier, if a multimode wideband scanner is available, or a receiver capable of receiving all-mode at 42 MHz or MHz is available, then the local oscillator reference crystal will not need to be changed. Once the filter is tuned, the signals from either the 13 cm SSB or satellite portions will be easily received. Figure 3 - The local oscillator at MHz can be used without modification to receive 13 cm signals.

A crystal is easily obtainable from Hy-Q now Precision Devices International and the frequency calculated from the function below For a local oscillator of MHz and MHz no further adjustment to the LO circuitry is needed, other than the crystal change. The photographs show the authors unit, tuned at MHz with a MHz local oscillator, with the transveter LO tap see end of this article.

The received IF will then be available at MHz. Once the crystal is changed, the operating frequency can be easily adjusted with a frequency counter by means of the trimmer adjacent to the crystal. Remembering that if measuring the frequency of the crystal oscillator, any error in trimming will be multiplied by at the local oscillator frequency.

A 1 Hz resolution at MHz is desirable if measuring crystal frequency. Several alternatives for measuring the local oscillator frequency are available, and the author posesses a Watson 3 GHz counter which with a 30 mm insulated probe works most satisfactory. An EIP Microwave counter was also used with higher precision still. Wavemeters will not be accurate enough at the LO frequency for any more than an indication of operation. Of course if your alignment signal is calibrated then the signal can be netted by zero beating, or even an HF receiver could be used to get the crystal frequency close.

Desireable characteristics are a sealed unit that prevents leak-in of strong signals on the IF frequency from local sources, sufficient bypassing at RF of the DC supply, and low insertion loss. Accompanying figures show a suggested layout. There is some leeway in component values and tolerances are not critical. A PCB will be made available if desired. It is recommended to use SMD capacitors and good feedthroughs for best results, however the experimenter can work with whatever materials are closest to hand.

Keep all lead and line lengths short. Figure 4 - DC Injection to supply the downconverter, striplines are approx 0. It is indeed possible to use this downconverter as a basis for a 13 cm transverter, and as such offers good performance at an advantageous price.

A tap from the local oscillator can be obtained by insertion of a 30 mm probe situated above the first local oscillator bandpass filter's stripline, and spaced equidistant from the top surface of the pcb and the top of the lower casing. It is awkward to mount a suitable connector in such a confined space, however an SMC connector will fit into the available space easily.

Some removal of the diecast casting on the exterior is required, caution being required not to overdo the 'milling' or getting metallic dust inside on the surface of the printed circuit board. This was ample to drive a balanced mixer to produce MHz with milliwatts of MHz drive.

There are several designs for 13 cm transmit mixers, however the author has developed a suitable transmit mixer with parts salvaged from an Ionica subscriber unit, with a low level amplifier capable of driving a PA to whichever power level as necessary.

However, the design is still in the beta stage at present, but the design is available on request. A suitable design by Peter G3PHO is included with these papers and represents a useful portable DC source for the voltages required by the downconverter.

Acknowledgement to Peter and his excellent Microwave Newsletter are given herein. Peter has much information available at his website - The world above MHz. Using strips of thin copper or brass. Then clean both sides thoroughly with a fibreglass pencil until it's really really clean, and tin with the least amount of solder possible.

Run the iron up and down the length of the stip whilst holding it by the end in a pair of tweezers, and first let gravity do the work and let excess solder run to the bottom. A sharp flick of the tweezers whilst the tin is molten shakes off the bulk of the excess.

Second, run the iron up and down the strip once again, and flick the excess off, so there is as little solder as possible on the strip. Trichloroethane - sold as 'tipp-ex thinners' , soaking a bud in the mixture and then cleaning thoroughly all traces of flux and residue from the strip - you'll be surprised just how much comes off! Whilst at the chemists with this little shopping spree, get some wooden toothpicks too, a small box will last years.

Open up the unit, making note of the general layout of the filter. The filter consists of alternate 'u' and 'n' elements - referred collectively as a 'hairpin filter'. No board traces need to be cut, which is a godsend because the modification is at least reversible. If you make a mistake, remove the wrong piece and start again. Remember, use a good earthed soldering iron, and earth the work, preferably by strapping the negative of the power supply to earth.

A good earth arrangement is essential to save any damage caused by static. It's just plain good sense too.