|Joined:||Sat, Apr 4th 1998, 00:00||Roles:||N/A||Moderates:||N/A|
|HF Beam Antenna Polarization||Aug 19th 2014, 02:05||6||773||on 21/8/14|
|Fringe TV reception and 2 meters (filtering?)||KD0FGH||on 4/4/15|
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|
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.
|What Characters do I need to Know?||WB5EMX||on 16/3/15|
If you're desperate for some unusual Characters, may I suggest Disneyworld in Orlando, Florida as they have a whole bunch of them, No CW Key Required, Mickey Mouse, Minnie Mouse, Donald Duck & Goofy just to name a few and there running loose all over the park! LOL
The only requirement is to be Young at Heart.
|SWR and metal roof||KO0Y||on 16/3/15|
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.
|Load Matching on lower VHF Bands||WB5EMX||on 15/3/15|
I guess you could use a Dipole on 6 m & 2 m but I wouldn't expect the best results when trying to work DX stations. Most operators start out with a 4 or 5 element Yagi antenna on 6 m and a 8 to 12 element Yagi on 2m. It's best to horizontally polarized these beams because there a 20 dB attenuation in cross polarization, very noticeable on the VHF Bands.
Height is part of the name of the game on VHF & UHF although you can mount a 6 m antenna at 20' and work DX when the conditions are right, your Terrestrial signal over the horizon will be lacking so I normally recommend to mount the 6 m beam at 35 to 40' and if you have a tower with a multi-band multi-element on top, I recommend to mount the 6 m 9' above the HF beam otherwise mounting it at 5' above the HF beam you'll discover interaction between the 10 m & 6 m antennas. For 2 m SSB, I recommend mounting the Yagi at 35 to 40' minimum and if you would have a tower with a HF Multi-band beam I recommend to mount the 2 m Yagi 4 to 5' above the HF beam.
I've used a HF VSWR Bridge on 6 & 2 m in a pinch but it's better to have a VSWR Bridge rated at those frequencies and better yet a Bird 43 Wattmeter with the proper slugs.
There are Antenna Tuners that cover 6 m & 2 m but they are normally separate units and only capable of 200 W. You can find the in the ARRL Handbooks and I've seen some sold through MFJ Enterprises, these aren't as commonly used on the VHF & UHF Bands.
Antenna matching is normally accomplished using a Gamma, T & Delta Match (with a coaxial balun) for either 600 Ohm or Coaxial cables.
Interesting that you have inquired about either using open 600 Ohm Ladder Line or 52 Ohm Coaxial Cable. It turns out that 600 Ohm Ladder Line was the only line first available, it has very Low Losses for transmission line compared to some coaxial cables although this comes to a compromise point, thet is when the open feedline get wet or ice forms on it, this throws the 600 Ohm line way off causing VSWR problems towards the transmitter. This is where 52 Ohm coaxial cables are better although many different coaxial type cables do have considerable insertion Losses so you got to understand how the "dB" Losses affect the RF Output of the transmitter and receiver signals. Here's a Coaxial Cable Chart:
You notice that there's 9913 & LMR-400 which appear to have the same Losses but I will recommend to use LMR-400UF (which indicates it's Ultra Flexible) for making a loop around a rotor whereas 9913 has a Solid Center conductor not easily flexible.
Even a better coaxial cable for a run between the ham shack and the top of a tower would be 1/2" Andrews Heliax .5 dB Per 100' at 50 MHz and 1 dB Per 100' at 144 MHz or 7/8" Andrews Heliax .27 dB Per 100' Andrews Heliax at 50 MHz and .5 dB Per 100' Andrews Heliax at 144 MHz. You can find this type of 50 Ohm transmission line & connectors USED at either a commercial tower installation company or a commercial two-way radio shop. Try not to pay more than 50 cents Per Foot for the 1/2" and $1 Per Foot for the 7/8" Used Andrews Heliax Coaxial Line. Working with either of these transmission cables normally requires two people and do NOT try to make 90 degree bends or it will damage this transmission cable.
As you come along, you'll discover that the Antenna System is the King Pin of your station, spend as much time and money on your Antenna System as possible and you'll end up with a first class VHF station working the DX.