Wednesday, November 3, 2010

Microwave antenna alignment (Cont)

Alternative Methods:

Traditionally, the radios that will be placed at each site are used to complete the task of optimizing the path.However, there are several reasons for not utilizing the radios to complete the process. The radios may not be available at the time the test has been scheduled or their reliability may be questionable, thus alternate methods are needed. Another possible reason the radios might not be able to be used is that the FCC permit shave not been granted, but the contractor needs to complete the path test on time to meet the customer’s requirements, or ahead of expected turbulent weather. In addition, if the anticipated path is questionable, a quick, cost effective, reliable method is needed to test the link, prior to the significant investment of constructing towers, purchasing radios and other expensive equipment and hardware, etc.

Alternative test instrumentation must be utilized, in lieu of the radios, whenever the previously mentioned circumstances arise. Scheduling of the path alignment test and installation of the associated hardware (cables,waveguide, antenna, etc.) can be facilitated to reduce excess mobilization costs. Some of the most widely used equipment for this application are signal generators (used as the transmitter) and spectrum analyzers(used as the receiver). The signal generator should be a broadband, synthesized device (phase locked to a reference clock) with accurate output power, equal to or greater than 0 dBm. The spectrum analyzer should betunable, and have at least –100 dBm of sensitivity at the frequency band of interest. Signal acquisition speedof the receiver is essential to quickly spot subtle changes in antenna response or to support investigation of problem paths. Most importantly, ease of use is vital in order to reduce the training costs of test technicians.Much of the test equipment used in this alternate method of path alignment tends to be expensive and complicated.

Application Specific Solution:

Recent test instrumentation has brought on feature rich, expensive systems that shoot for the stars in offeringthe latest and greatest in technology. However, these systems are mostly not fit, nor are they practical, forspecific applications such as antenna path alignment. The most successful new instrumentation in the industryhas been equipment that is application specific, portable, battery powered, and easy to use, withoutcompromising performance. The Path Align-R™, is a new addition to this practical, application specific category.It is specifically designed for use as a microwave path alignment test set. Among its many features andfunctions, eight specific traits fit those identified as important to microwave antenna path alignment.

1. Portable - Each of the two units in the Path Align-R™ Test Set weighs only 7 pounds, fully loaded, andis 3.5” x 8.375” x 13.1” (HxWxD) in size. This significantly reduces the shipping costs and logisticsof transporting test equipment to and from the site.

2. Battery Powered – A rechargeable lead acid battery is fitted to provide four to five hours of operation.Not only is this ideal for field use but each unit can easily be taken up the tower, in its weatherresistantinstrument back-pack, and attached directly behind the antenna using a carabiner and a nylonrunner, strap, or lanyard.

3. Ease of Use – A pair of units (sold as a ‘set’), one at each site, reads out the path loss, identically, atboth ends of the link. Simply turn them on, connect the output to the antenna using the supplied cable,tune the frequency, connect the headset, and you are ready to test. Rarely has an instrument been soeasy to use without compromising on performance.

4. Performance – A Path Align-R™ test set provides 100 dB of effective dynamic range. This is the resultof the 100 dBm sensitivity of the receiver and 0 dBm output power of the transmitter. Four bands(1.8–2.5 GHz, 5.8–6.6 GHz, 11–12 GHz and 18.1–19.4 GHz) are provided in the standard Test Set.The specific operating frequency can be tuned by the operator within these band limits, using thethumbwheel switches, to a resolution of 1 MHz. An antenna system whose link frequency is designed outside the frequency band edge of the Path Align-R™ (e.g. 6.8 GHz) can still have its path alignmentcorrectly adjusted, as long as the antenna system (antenna, waveguide, etc.) can operate at both thelink frequency (6.8 GHz) and a nearby frequency covered by the Path Align-R™ (e.g. 6.6 GHz).

5. Speed - An LCD readout of direct path loss, with a 0.1 dB resolution, automatically updates itsreading every 300 milliseconds, and can quickly find subtle changes to the antenna response, thusallowing for small adjustments to antenna azimuth or elevation for optimum signal transfer.

6. Voice Channel – Communication between sites, and from radio room to tower top, is significantlyimproved, with a full duplex voice channel. Each tower technician can speak to the other through theincluded headset, without having to key a radio. Voice communication is enabled immediately aftersetup and activation. The antennas do not even have to be fully aligned for the voice channel to work.

7. Accurate – The Path Align-R™’s output is a synthesized source that provides a very accurate and stablesignal. When compared to a synthesized source (HP 8360) and a fully featured spectrum analyzer (HP8594E), the Path Align-R™ test set measures path loss within 1.0 dB of each other.

8. Cost Effective – The Path Align-R™ test set is priced far below that of a synthesized source and spectrumanalyzer combination. However, price is not the only savings achieved with the use of the test set.The cost of communicating between sites can become quite expensive when using cellular technology(about $300 per event when considering long distance, roaming, and calling time charges that aretypically the case in a remote microwave test). The use of two technicians operating the radios, andtwo tower climbers working behind the antennas, can potentially be reduced to three; with thesupervisor level on the ground floor and two tower climbers. The transportation costs of shipping thetest sets to job sites from the central office can significantly reduce company expenses.

It is apparent that the Path Align-R™ test set is well featured to offer impressive results in accomplishing the goalof an optimum solution for the microwave path alignment test process.