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HF Beam Antenna Polarization Aug 19th 2014, 02:05 6 1,118 on 21/8/14

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Fringe TV reception and 2 meters (filtering?) KD0FGH on 4/4/15
Hello Alan,

There is such a Filter available through Microwave Filter Company which is a FasTrap Model # 5KMT-A/H, you and your friends can purchase these 75 OHM Filters and install them either directly into the Input connector of a Pre-Amplifier or if you don't have a TV Pre-Amplifier then connect to your TV 75 OHM Input. I started using these filters in the early 1980s while I serviced 300 W RF Wide Area Radio Paging Systems with remote locations 60 to 80 air miles away from the major metropolitan areas that broadcast the older Analogue TV signals. Most of the time I would interface with the personnel that were taking care of the TV Pre-amps and individual TVs for the customer. Those technicians were amazed once the filter was installed as you couldn't tell if the 300 W Radio Paging station was in use or not.

Years later I purchased several more for my own ham station as I operated 2 m SSB with 1.2 KW Output and living 45 to 50 air miles northwest of Chicago I knew I would cause Front End Over Load to my neighbors TV systems for Over-The-Air Signals. As my neighbors complained, I would take a HT with me, a fellow ham would operate my station. I would communicate back to him to stop transmitting with my neighbor standing next to me, install a filter and then tell my fellow ham to start transmitting again. Again you couldn't tell when my Kilowatt Amplifier was or wasn't in use.

I will admit that there were two different situations that came up, that were impossible to solve. The first was when an individual had a Wideband Pre-amp incorporated into their Winegard Antenna as it clipped into the 300 OHM mechanical antenna feedpoint. If you're fighting that type of situation, there is NOT a filter made to over come that configuration. The second problem was encountered with people that had "Rabbit Ear" Antennas inside their homes. Back in the 1980s even the FCC would not consider "Rabbit Ears" as adequate TV antennas so in essence that's another problem that can't be corrected so keep this in your memory.

They're still making "Bow Tie" antennas with Pre-Amplifiers built into these in house antennas. In this situation all I can do is recommend helping the owner install an outside real antenna with 75 OHM coaxial cable and install one of the filters. Here's Microwave Filter Company's website:

SWR and metal roof KO0Y on 17/3/15
Hi Tim,

I would stay away from using a plastic sleeve on the antenna system since the mast pipe and roof are made of steel. Okay about changing the antennas but still having the same problem which leads me and Bill WA0CBW to believe the problem lies in the feedline, even pinhole penetration through the outer jacket could have happened which in turn allowed moisture to creep in undetectable by the human eye.

Your guess at the 9913 being 55 to 60' feet is ONLY an estimate and I'd be only guessing as to what to add to the transmission line this is why you need to have the EXACT length.

If you had a known good 50 Ohm Dummy Load and disconnected the RF cable from the GP-6, connected it to the 50 Ohm Dummy Load, re-measured the VSWR again and it read high, this would point the problem directly at the transmission line.

I did a little research on Bill WA0CBW, he's a pretty sharp individual as he taught electronics, then became a Project Manager for Motorola Cellular & the Land Mobile Two-Way Radio Sector and ended up a Motorola Service Shop performing the same tasks before retiring (Lucky Him).

I spent my 34 year career working for Motorola in Schaumburg, Illinois wore many different hats during my career, engineering technician in a corporate R & D lab, consultant for the International Engineering Department, spent time out in the field implementing simulcast radio paging systems, a couple of years in the infrastructure cellular department, working for the Midwest and Hi-Tech depots doing repairs on the high power RF amplifiers and Securenet product line, a few years for the iDEN / Nextel Digital Infrastructure systems implementing MSOs around the U.S. & Canada and ending my career in the Secure Design Center handling Infrastructure SP Bid & Quotes, Design & Development of new configurations on Base Stations and Portable Products, Maintenance of the Production line for Secure Products - Crypto technology and doing Export Control Assignments for the Secure Products before being relieved of my responsibilities in June, 2004. I don't have a positive word towards Motorola or Motorola-Solutions, Inc.

SWR and metal roof KO0Y on 16/3/15
Hello Tim,

I have only a little experience with metal roofs in the Midwest, in and around the Chicago area on commercial buildings but I've never encountered the VSWR changing with Snowfall or moisture which makes me wonder if there is moisture inside of your vertical antenna or if your vertical mast pipe is touching the metal roof setting up some strange bi-metal impedance, sort of a Diode action. If the roof is steel and the mast pipe is aluminum this could happen.

The other strange thing about your VSWR at the antenna and in the ham shack points to the length of your LMR-400 as it could be either too short or too long in the electrical wavelength. I've seen this happen at repeater sites when the feedline is a little bit short and a small jumper has to be made or by adding a couple adaptors to make the feedline appear at the correct length electrically not physically.

If you know the exact physical length of the LMR-400 (measured in Feet) equals 246 divided by Frequency times the coaxial Velocity Factor which is .85 this will give you the electrical length in Quarter wavelengths. A lot of hams do not realize that the Center Conductor of LMR-400 or 9913 is a Solid Piece of Wire making it non-flexible and if for some strange reason it developed a break inside of the feedline that could cause even a bigger problem. Make sure you don't have any 90 degree bends in the feedline as this is NOT recommended.

I've been recommending to use LMR-400UF (Ultra Flexible) which has a Stranded Center Conductor. Lets hope this isn't part of your antenna VSWR problem.

Parts List Entry for Hand Wound Magnetics WN8P on 11/3/15

I use to do what was called a Bill Of Material or BOM that broke down the Option, Kit, Assembly Number and Piece Parts for in house manufacturing, then I also wrote special instructions for the factory to build these Assemblies and Kits and if the Kits were sold as Options for the Technical People out in the field then I would be required to write a Field Modification Manual that would accompany the Option & Kit. For the life of me I just can't remember what software package was loaded into the computer for performing this function. I was employed in Engineering at Motorola in Schaumburg, Illinois at the time.

Parts List Entry for Hand Wound Magnetics WN8P on 8/3/15
Hello Larry,

What you are describing is a Bill Of Material Break Down Chart often used by major manufactures that provides a high level component number and then the actual parts used in the high level part. I've also seen it listed as a Kit, Assembly Number and Part Numbers that are required. I believe what you want is for the ARRL to instruct anyone writing an article to use a Standard Bill Of Material used in their Design. There are software programs that can do this function but they're not inexpensive and then the ARRL would be required to provide a Standard Format for each type of a Component, Assembly and Kit that eventually get soldered to a PC Board.


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