Best VHF UHF receive antenna?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KE7RUX, Oct 1, 2019.

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  1. AI3V

    AI3V Ham Member QRZ Page

    I have done enough "coverage plots" to understand they are one of the methods "public safety" radio salesmen use to pad the bill of departments spending OPM - Other People's Money.

    Around here the scam is to guarantee some percentage of coverage, let's say 99.6%

    Then when Billy Bob complains there is no coverage in the East Podunk subdivision, the salesman gets all serious and informs him that East Podunk is in the .4%, and he needs to buy a expen$ive satellite receiver, tower, antenna, coax, lightning rod,voter and rf link back to the voter.

    With luck you can stroke him for a equipment shelter and electrical service.

    If you need to put in a access road, the salesman gets a new boat.

    Rege
     
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    You keep referring to salesmen, etc. I have NEVER been a salesman! My career was always on the technical or manufacturing side. I got married my junior year at Georgia Tech. The quarter (Georgia Tech was on the "quarter" system, not semester system, at that time) before getting married, I dropped out to get a job to build up some money to supplement what my (soon to be) wife was making. It just happened that the Motorola Service Center was advertising for a technician. Also, the MSS was 2-blocks from campus. After going back to college, they let me take off to make daytime classes.

    Then, at the start of my senior year, Motorola came to me and wanted me to establish, and then manage, the very first company owned portable / pager repair facility away from the Schamburg, Illinois, plant. This was at the Motorola C&E "area office" located on the south side of Atlanta in Forest Park, Georgia. I told them that I had classes that were only available during the day. The area vice president handed me a key to the building and told me to take off whenever I had a class and, if I needed access to the building "after hours", the key would unlock any door in the office. It did not hurt that he also was a Georgia Tech graduate and had exactly the same major as I.

    After graduating with a master's degree, Motorola had a hiring freeze and could not offer me a job equal to my degree. However, Collins Radio Company was interviewing on campus. Collins had my wife, and I, fly out to Dallas to look over the "new" corporate headquarters here in Richardson, Texas. They offered a very good salary and I was satisfied with the position. Then, a couple of years later, Collins was running into some serious financial difficulties (I was in a position to know this). Collins did give me 2 raises at my 2-year anniversary. Then, one of the Collins department managers left and became a vice president at a micro-electronics manufacturing company. He offered me about a 50% increase in salary over what I was making at Collins. As such, I became the applications engineer manager at that company.

    Then, the company was "bought out" by another company and all of the higher paid personnel were laid off. Fortunately, the person who handled the shipping and receiving for me in Atlanta had been promoted to the reconditioned equipment department head and was transferred to the Dallas area office. He was having problems with the contractor doing the reconditioning and their contract was "up". He asked me to establish a company to do the work. I held that contract for almost 10-years when Motorola decided to abandon the reconditioned equipment business.

    For the next 10-years I owned a company that handled two-way radio / microwave radio service and also did light manufacturing. Then, in 1989, I was approached by Fluor-Daniel to be a telecommunications consultant at Texas Utilities. Then, 4-years later, was hired directly by TXU. In 1999, TXU eliminated the telecommunications department and I then established my own consulting company.

    I definitely agree that a goodly number of salesmen will do anything possible to make a sale. It has been my experience that more power does NOT help filling in "dead areas" virtually all of the time. Maybe, in like 10% of the situations more power "might" be able to improve a marginal signal to a usable signal.

    But, why is there an area that is not covered? In almost every case this area is in a "shadow" and what causes the shadow? The answer is that the line of sight propagation is interrupted by terrain, large man-made structures, and so forth. Can you explain why terrain, etc., causes dead areas and not line of sight propagation? I sure would like to know your theories!

    A bare minimum system might promise 70% area coverage 70% of the time. That really gives a 49% reliability factor. The best systems, that do not cost astronomically high prices, would promise 90% area coverage 90% of the time. That represents an 81% reliability factor. A very high priced system might promise 95% of the area 95% of the time. That gives a reliability factor of just over 90%. To get a 99% reliability factor would require a system that covers 99.5% of the area 99.5% of the time. Although theoretically possible, even using satellites this reliability factor is a practical impossibility for a number of reasons.

    Salesmen often use charts and / or formulas to predict coverage. Even the best formula cannot really predict problems with terrain and similar things.

    Motorola came out with the low band Mocom 10 system in late 1969. They established a special group of salesmen who only sold these units which were intended as a much better alternative for small businesses than "CB". The Mocom 10 was available with 5-watt output transmitters or 25-watt output transmitters. As a sales tool, each salesman was provided with a range indicator that predicted the coverage area. These units consisted of a battery in series with 2 fixed, switched, resistors, a potentiometer, and completing the circuit a meter calibrated in "miles". When the switch was in the 5-watt position, the higher resistance was in the circuit and when the switch was in the 25-watt position, the lower resistance was in the circuit.

    The potentiometer was calibrated with the height of the tower, or other antenna support, in feet. As this control was turned towards higher and higher feet, the resistance of the variable resistor decreased. Therefore, with the switch in the 25-watt position, as the "height control" was turned indicating a higher antenna height, the meter reading increased.

    Motorola gave a 100% guarantee on these systems and that bit the company in the posterior! Most of these systems did not come anywhere near of predicting the maximum distance from the base station let alone any real terrain predictions. To satisfy the customers, Motorola provided, at no additional cost, reconditioned 100-watt output Motrac mobile units and 100-watt output Consolette base stations. This was great for my business but very costly to Motorola.

    Getting back to the original line of sight discussion. How do you explain dead areas, usually caused by terrain factors, that exist without line of sight propagation?

    Glen, K9STH
     

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