What's all this COAX stuff anyway? by Gerry Crenshaw, WD4BIS

What's all this Coax stuff anyway? What type of Coax do I use? What do the Coax type numbers tell me? Why 50 Ohm coax? Most of us use coax every day, We bought the antenna with coax attached or the radio instruction book said to use it. But why coax and not open line feeder cable in the 300 to 600 ohm range like they used to use? For that matter what's wrong with a wire right from the back of the radio. A wire from the back of the radio presents some special problems. First the wire from the radio becomes part of the antenna and radiates as well as the antenna. This causes interference as well as affecting the antenna pattern. Second, a high voltage point appears in the antenna wire at, or near the connector. This is a serious fire hazard when you consider that most of us have to pass that wire through a wall of some kind and the wall is usually have wood or some other combustible in them. Open line feeders solved some of these problems by balancing the currents between the feeder legs. The radiation field also tended to stay contained between the legs of the feeder line until the wire was split into antenna elements or legs. This minimized the interference or strong radiation fields in the shack. Tube amplifiers were also high output impedance devices, on the order of 2000 ohms. (Plate Load = Plate voltage (Typ. 1000v)/Plate current (Typ. 500ma)) so matching a tube amp with an output impedance of 2000 ohms to a 600 feed line only required 3.3 to 1 transformer. This still leaves us with the problem of high voltage on the antenna line. Assume a power of 1000 watts, an impedance of 600 ohms and remember the formula for Voltage of E = square root (PxR). This leaves you a voltage of 774.596 volts. If the line Impedance is changed to 50 ohms this reduces the voltage on the antenna line to 223.6 Volts.
Coax came about to eliminate some of the high voltage problems and radiation problems. Coax by design is self-shielding since the outside jacket is at ground potential. Because the inside conductor is insulated and shielded, hazardous voltage levels don't appear on the coax except at the antenna connection itself.

Why 50 ohm Coax?

This is best answered in two parts, First, coax isn't all 50 ohm, it ranges in impedance value from 30 to 90 ohms. Second the lowest possible transmission loss occurs at about 70 to 80 ohms while the highest power handling occurs at about 30 ohms. Because of these factors a compromise between line loss and power transfer was struck at 50 ohms. This explains however why Cable TV firms who have huge distribution networks still use 75 -ohm coax.

Coax Types

Coax is available to us by different Type Numbers. Most of us are familiar with 50-ohm cable types RG-58, RG-174, RG-213, RG-214, and 9913 and the 75-ohm cable types RG-59 and 783. Cable with a "RG" in the type number means "Registered" and all this really means is someone filled out the forms to register it, by itself this means nothing. Cables that are Mil Spec. qualified for lot certification (Per MIL-C-17D) will be listed as RG-XX/U. The numbers between the letters were assigned in numerical order, from 1. This can be used to indicate only the products registration. For example an RG-8 coax was registered before the RG-213 coax.
Coax that is marked "RG-8 TYPE" means that these cables are similar in impedance, size, power handling etc. to the Mil Spec. qualified cables, but have never gone through the actual certification. For our application these will work fine.

If you have looked at these coax types, they come in several diameters. Generally if you are going to be handling high power (200 plus Watts) or your coax runs are going to be very long (Over 100 feet) you need to be using one of the larger coax such a RG-8, or RG-213. If you are working the satellites and low line loss is a major concern, a coax such a 9913 or RG-214 should be used. The RG-214 coax is a double shielded RG-213 type coax and usually is a lot of trouble to find connectors for, and to work with. For general use such as short runs for the car, a few jumpers for the shack or a length of coax for emergency use, RG-58 coax is a good choice. RG-58 is the least expensive of the coax types and serves very well for low to medium power applications in the HF to UHF regions.

Surplus Coax
Coax can be found on the surplus market. But again caution should be the watchword. Much of the coax found on the surplus market are leftovers from the Cable TV industry. Avoid any coax with a Teflon dielectric. These were made for High Temperature/Hostile environment applications and usually have inferior signal handling characteristics compared to standard coax. Hard-line/Heliax type coax can be found in 50 ohm impedance, and there are coax connectors available for this type of coax. About the only application that justifies this type of coax is a repeater installation. Its expensive, hard to bend, hard to connectorize, hard to secure to a tower and its just plain heavy. Any of the 50 ohm coax will work for our application. Choosing the best coax for you application will enhance your station operation. Using the best coax for your application can make the difference between being heard and being QRM.

Copyright 1996 Gerald Crenshaw WD4BIS. All rights are reserved.

Remembering the OWs of Early Ham Radio

By

Donna L. Halper

This appeared in the March/April 1998 issue of "YL Harmonics'', the newsletter of' the Young Ladies' Radio League, Margaret Dunn-KC7L.XS Editor.

When we look back on the history of amateur radio, certain names come up immediately: Hiram P. Maxim and Clarence Tuska, the founders of the ARRL; "America's Number 1 Ham", Irving Vermitya (and many CQ and QST readers undoubtedly made contact with W1ZE during his long and illustrious career); the great inventor Edwin Howard Armstrong; and of course, Guglielmo Marconi himself. But there were some other pioneers who have seldom gotten the credit they deserve-- a small number of women who entered the game at a time when few in society thought they were capable. These women learnt Morse code, built (and sometimes won awards for) their own receivers, and surprised many people who believed radio was a man's hobby. And while most were not inventors, their presence in the family of amateur radio made a positive impact, and inspired other women to follow in their footsteps.

Unfortunately, telling their stories has sometimes been a challenge, as Louisa B. Sando (W5RZJ) found out when she began researching her excellent book "CQ-YL". Although women amateurs absolutely did exist even in the earliest days, they frequently operated stations run by their father or brother or husband, and did not have call letters in their own name. In QST April 1923 issue, for example, it mentioned that Lillian Hume was an amateur who worked from her brother's station, 9DTI; however, that station was only listed in his name-- George Hume. Further, some women who did have a station in their name subsequently got married and moved to a new city, leaving no information about what their new name was. (And while I am sure most men were very understanding about their wife's hobby, several of the women I interviewed about those 'good old days' told me that when they married, their husband discouraged them from continuing on with ham radio-- supposedly this was not a properly feminine activity for a wife and mother... How times have changed!!!)

Like Ms. Sando, I too encountered the problem of not finding the names of women amateurs: I noticed in my research that some of the younger women who grew up in the late teens and early 1920s made use of school stations-- but the call books of that time did not list the members of school or club stations by name. So, unless a young woman was written about somewhere else, there was no way for me to find out who she was, or how many clubs had women participants. I might never have known that 8ME, a high school station in Beaver, PA, was where a certain 15 year old named Rena Jane Frew got her start, nor would I have encountered the name of Bertha Hilton, who worked out of the Chester, PA Radio Association station, 3ZO, had they not been mentioned in "Popular Radio" and "Radio Digest" as part of articles about the clubs they belonged to.
This lack of information about women is understandable when you consider that compared to their male counterparts, their numbers were small, and many did not know how to-or perhaps they preferred not to-- get publicity for themselves. Also, nearly every ham radio columnist back then was male, as were most of the officers of ham radio clubs; since it was usually a club's officers who sent information and pictures to the media, the vast majority of the amateur news was by and about the men of ham radio. Anyone reading the publications from those days could easily have gotten the impression that ham radio was an exclusively male preserve. But as Paul Harvey would say, now you are going to hear "the rest of the story".

Had AMRAD not run into financial problems that ultimately took WGI off the air in mid-1925, she might have continued on in professional radio, but instead, she ended up working as one of the few women engineers at the New England Power Company, while remaining very actively involved as a ham-her call letters became W1MPP in 1938. For those who collect back issues of CQ, in April of 1948 she was named YL of the Month... later that year, Eunice married Ken Thompson (W1PS), also a de-voted ham, and after they both had retired, they divided their time between homes in Maine and Florida.

End of part 1. Part 2 will appear in the June issue.

###### EDITORIAL

THE AMATEUR RADIO CODE OF HONOR (Updated)

A previous issue of the ARNS Bulletin presented the Amateur's Code. This version was written in 1928. Larry Amann-K5TQN provided the following version, an update of the earlier version, which has been published in ARRL workshop proceedings.

1. As an Amateur I will respect the rights, privileges, and dignity endowed upon all races, creeds and gender. And, in doing so, I will recognize that it is not a right but it is a privilege for all to operate Amateur Radio equipment in accordance with the authorization prescribed in the FCC Rules and Regulations.

2. As an Amateur I embrace the joint membership of our beloved fraternity-sorority. And, in doing so, I will support and protect our family of radio amateurs against all encroachments which could threaten our dedication to the encompassing purpose of sharing and caring for the good of all mankind without financial compensation.

3. As an Amateur I will be considerate. To the best of my ability I will never use the air in such a way as to lessen the pleasures or encroach upon the good taste of others.

4. As an Amateur l will be loyal. I will extend my loyalty, encouragement and support to my fellow radio amateurs, my local radio club and to the American Radio Relay League through which Amateur Radio is represented.

5. As an Amateur I will be progressive, I will endeavor to keep my Amateur Radio equipment abreast of the technological advances in Amateur Radio Communications and Amateur Radio Space Science.

6. As an Amateur I will be friendly, slow and patient sending when requested, giving friendly advice, counsel to the beginner, and kindly assistance and cooperation for the interest of others.
7. As an Amateur my interest in Amateur Radio will be balanced. I will never allow it to interfere with any of my duties I owe to my home, my job, my school and my community.

8. As an Amateur I will be patriotic. My knowledge of communications and my station will always be available for the service of my country and my community.

MINUTES OF GENERAL MEETING 4/21/99

BY PETE, N2PYV

The meeting was called to order by Pat at 5:07 PM.

All persons present introduced themselves.

TREASURER'S REPORT: Ted, KD2UB

Ted read the financial report and indicated we are doing very well.

REPEATER REPORT:

Gordon, KB2UB

There is nothing new. The repeaters sound OK.

VE REPORT:

Bob, W2ILP

Two applicants passed three elements. There were six VE's present.

NET REPORT:

Zak, WB2PUE

Thursday night 2 meter net had about four check-ins. The Sunday morning 40 meter net was excellent. Today's 20 meter net only had two people on.

HOUSE REPORT:

Pat, KE2LJ

The Company still plans to vacate Plant 5 in 2001. Moving will start in the fall of 2000. Our meeting place should be OK until then.