A NorCal Project ...
St. Louis Vertical Updates

Compiled by Jerry Parker, WA6OWR

About the AmQRP Club
Frequently_Asked_Questions
Kits
Projects
QRP Forums
Contesting
References
Links               


Table of Contents

Click on this Title to find the article

Contributor

The St. Louis Vertical Revisited by Dave Gauding, NF0R
Resonance on the St. Louis Vertical by Grover Cleveland ,WT6P
Additional St. Louis Vertical Stuff by Dave Gauding, NF0R

 

The St. Louis Vertical Revisited by Dave Gauding, NF0R

Here are a few ideas and observations on the St. Louis Vertical:

RADIATOR:

MOUNTING POST:

RADIALS:

FEEDLINE:

LOGISTICS:

MODS REPORTED: This is a reprint of an article first published in the Peanut Whistle, Sept. 96 issue, journal of the St. Louis QRP Society. Permission is granted to reprint in non-profit journals as long as the Peanut Whistle and the Author are given proper credit.


Resonance on the St. Louis Vertical by Grover Cleveland WT6P

I spent the afternoon assembling the St. Louis vertical. I discovered what others had reported - the antenna is resonant at about 5.6 MHz. So I started pruning to achieve resonance at 7.040 (or thereabouts) using a loosely coupled GDO. The antenna had four radials as specified in the instructions

The final results of all this were that I threw away 26.8 feet of the original 50 feet specified for the loading coil. The final coil wind goes like this: nothing for the first 1.5 inches above the end cap, 13 inches of tightly wound twin lead, the remainder of the twin lead spread evenly up to the top of the first section. The upper wire is a single strand of 18 ga. about 17 feet long spiralling gently down from a solder lug at the top. It is resonant at 7.040 MHz.

Your mileage may vary but I can assure you that fifty feet of twin lead is far too much to begin with. Start with no more than 35 feet or so and begin pruning. Use an analyzer or a GDO.

This is a great antenna! It is going to be heading up to the Sierras next weekend for a "field" test. I am very pleased with the design. Thanks are due to the St. Louis QRP Club for the original work and to Norcal for the current marketing effort. You will love this antenna.

73 and cheers,

Grover
WT6P


Additional St. Louis Vertical Stuff by Dave Gauding, NF0R

HERE ARE A FEW IDEAS AND OBSERVATIONS ON THE ST. LOUIS VERTICAL:

Here are some responses to questions about the twinlead coil in the SLV........and some other stuff!

Twinlead Coil:

Twinlead is used in the coil for several reasons. The material is self-spacing. When butted together it produces an inexpensive symmetrically spaced coil which radiates. It handles QRP power nicely and is very durable after installation on the rod base.

Several textbooks note that when parallel conductors are shorted there is some electrical advantage over a single wire, i.e. slightly increased bandwidth. However, the SLV was designed as a center-fed mulit-band antenna for 10-40M, a "seven-bander". The tuner automatically takes care of the bandwidth situation.

With this in mind the shorted twinlead coil in the SLV is used primarily for mechanical reasons to add strength to the solder joint between the wire and solder lug. The earliest version of the antenna used shorted twinlead for the radiator as well as the coil. A "more is better" gear was engaged at that time! The follow-up to the original article now posted on the NorCal web page covers conversion to a single wire radiator. This mod is simpler, cheaper and seems to perform well by comparison.

For those experimenting with mono-band SLV's the shorted twinlead should be a definite plus in the bandwidth department. Given the incredible number of portable 40M QRP rigs now in use a design mod optimized for this ban will surely be well received.

The twinlead specified for the prototype places approximately 51' of radiating conductor on the base of the collapsible pole. The vertical radiator adds another 16' for a grand total of 66'. Therefore the antenna offers a desirable half-wave on 40M, a full-wave on 20M and so on. It's almost as if the South Bend SD-20 and Black Widow poles were designed with portable QRP enthusiasts in mind. In any case, we'll take it!

I had no idea that the dimensions would work out so conveniently until after the prototype was on the air. Initial testing disclosed two important facts! First, locating the SLV's resonant point with the tuner on the seven bands was a time consuming process. Second, bandwidth at resonance is rather generous including 40M. In my experience the existence of both of these conditions predicts very good news when it comes to center-fed antenna performance.

One reason the SLV works as advertised is full electrical length and plenty of it. And, the spaced coil radiates effectively along with the single wire radiator. Veteran "slinky" ops already know it is possible to work stations with just the coil. I have done this on 40M on two occasions though these exercises were not intentional!

The antenna works on 80M as designed but has not been touted for that band. A tuner will resonate the existing 66' of conductor which is, of course, a quarter-wave on 80M. I have worked a few stations there to satisfy my curiosity. This was during the summer and more so an experiment than a practical demonstration. Perhaps others will carry this project a little farther now that winter is approaching.

Optimizing the antenna for 80M might include a full half-wave of speaker wire or zip cord for the coil. The additional electrical length will be helpful. Complimentary radials are in order as well. How such enhancements will impact performance on higher frequencies remains to be seen.

Radials:

There have been many questions about the radials as specified. Three radials seem to work just fine. A lot of early testing was done with only two. If "DX" is a primary interest then by all means add more radials!

The key word here is "logistics"! The SLV was designed first and foremost as a portable antenna. The questions then is how many radials does the portable op wish to install and then un-install at the operating site? As originally specified an SLV can be on the air in less than four minutes without working up a sweat. Builder's choice applies here!

Radial alternatives for 80M? Even a "shortened" radial has a big footprint. Try "slinky" toys very close to their full extension. There are three retail sizes but the classic baseball-sized coil does a nice job on 80M. Adding at least one of these coils to the original radial system is helpful.

No radials? Sure, why not? A classic zepp feed works well or try a tuner coax feedline with floating shield. Note that the latter does not require a tuner for balanced line! Either option works okay for casual operations and cuts set-up/breakdown times to almost nothing. For a little portable QRP at work during the lunch hour or in the evening after dinner this is the way to go. The angle of radiation is probably awful but the op at the other end won't know the difference.

New mods reported:

From KF9XY: Relieve the wooden mounting post slightly on a lathe to position the rod's base several inches above the earth. This keeps sand and mud out of the screw cap threads. It also helps insure the feedline conductors remain well separated. Three screws spaced equidistant around the post will accomplish the same purpose.

From KA0JWO: Build several mounting posts to respond to conditions at different operating locations. A sharp, thin spike is better suited to hard ground. A longer, heavier spike such as a gutter spike is appropriate for soft earth or sand.

Coming attractions:

I'm working on an "SLV Vertical Beam" and an "Elevated Mount for the SLV". These are fall and winter projects for the OM unless someone beats me to it!

I hope you will find this follow-up helpful. Please keep your comments and mods coming.

73 de Dave, NF0R

 
Material and concepts presented on The American QRP Club (TM) website is Copyright 2003 by The American QRP Club, Inc.
These pages are designed and maintained by George Heron, N2APB
Page last updated:  July 9, 2003