Welcome to another edition of Target DX! This time, we have questions on a variety of topics, along with some websites to add to last time’s list.
Q – What is this EWE antenna I keep reading about ?
A – The EWE is named using the English word which reflects the letter whose shape the antenna takes – ‘U’. The EWE antenna is directional off the end at the coax. The EWE that runs NE is directional to the SW. Basically the EWE is two phased verticals. That is, the two vertical elements with the lead across the top that connects them. The termination at the end is adjustable to get the directivity the way you want it.
With the EWE there is phasing going on, much like a broadcast station array. The far grounded end 20-foot vertical section is fed at the top, in a sense by the 100-foot horizontal wire. The near end vertical section, which is also 20 feet long, is fed at the bottom by coax. The 100 foot spacing between the two 20 foot vertical sections and top/bottom feedpoints create a 180 degree out of phase current lag which creates an endfire unidirectional receive pattern from the coax feed end, versus the resistor end on a terminated beverage. Unlike the Beverage antenna, the EWE needs a good ground conductivity under it to work properly (gain and directionality) and you can't really fix the problem with radials. It would play well on the Great Plains and near the ocean but lousy in the desert and mountains.
Q – What exactly is a ‘sloper’ and how does it work ?
A - The conventional 1/4 wave sloper will have a sloping wire to ground with an approximated 45 degree angle drop down to near ground level. The center c
conductor of the coax goes to this sloping wire, the braid of the coax goes to a metal tower, therefore you have an elevated feedpoint. The antenna is kind of like a dipole but with the radiating elements to close together. What happens with this antenna is the metal tower receives a vertical omnidirectional signal and the sloping wire a mix of vertical and horizontal radiation in the direction of the wire slope. Combine them and you get slightly off omnidirectional radiation/reception, with a 1-2 db gain in the direction of the slope of the wire. Modeling results predict 4-6 db gain in the direction of the sloping wire, but this is hard to attain, as this antenna is very sensitive to surrounding objects and poor rf ground connections in the tower sections. A sloper can be had without using a tower, or even a metal structure at all. If a tree of sufficient size is present, the coax can be run up the tree to the point where the diagonal element starts down. Performance may suffer a little, but those DX’ers who use this kind of installation don’t seem to complain much!
Q – I recently purchased a DX-398 from Radio Shack after seeing all of the positive discussion on it in DXN. The problem I have is that I seem to be replacing batteries very frequently. Is there a way to increase battery life, or some other alternative to use for truly portable and/or remote use ?
A - The DX-398 is a battery-killer! You can build a backup system using D-cells as follows. Parts are readily available at Radio Shack for a couple of dollars or so for each part.
Here’s what you need:
1 p/n 273-1740 power cord $2.99
1 p/n 270-0389 4 D cell holder $1.79
1 p/n 273-1716 "M" adaptaplug $1.99
[check to make sure this is the right one]
1 - 2 inch piece of solder
Electrical tape to wrap solder joints.
The power cord is 6'. You can make it as long as you want. The thing has two adaptaplug ends. Fold the wire in half and snip it, then strip and tin the ends of the wire. Take the end of the white stripe wire from the power cord and solder it to the red [+] side of the battery holder. Then take the black wire from, the battery holder [-] and solder it to the black wire of the power cord. Then wrap the exposed wires with electrical tape. Put the tip as negative and plug it in. When the plug is in, the backlight on the LCD stays on and you can see the thing at night. The DX-398 shuts the battery off after about 2 minutes to save the precious power from the AAs.
Q – I’ve noted several occasions over the past few months where various sources cite recent solar activity and predict auroral conditions, but the result is either nothing out of the ordinary or minimal or short-lived or both. What gives here ?
A – There are likely several factors. First, not every solar flare or other solar explosion is directed in the earth’s direction, and even though one is projected to affect us, not all do. Second, depending on how strong the forces are when they impact the earth’s magnetic field, there may not be a reaction sufficient to trigger ‘classic’ auroral conditions as we know them. Third, it often takes a more prolonged period of higher-than-normal A- or K- indices to create these conditions. Thus, a single, isolated event of relatively small or moderate size may not be enough.
Generally speaking, if the A-index for a given day exceeds 40, or if there are several days in succession of values in excess of 20, the type of conditions we speak of as auroral are far more likely. A further indicator is the Proton flux value. A solar flare needs to send the proton flux at or above 10 mev's for the D layer to absorb broadcast band signals at night.
Another indicator is the status of the earth’s geomagnetic field as per the WWV broadcasts or various government or hobby websites. If there is a major storm indicated as in progress and continuing over a period of 2-3 days, then auroral conditions are more likely to follow.
Here are some additional websites which didn’t appear in the listing in the most recent column:
List of Cuban Stations: http://davidtanny.8m.com/03facu.htm
Charts of the last 20 solar cycles: http://www.dxlc.com/solar/cycl1_20.htm
Charts of Cycles 21-23: http://www.dxlc.com/solar/solcycle.html
Great Circle Distance calculator: http://jan.ucc.nau.edu/~cvm/latlongdist.html
The editor would like to thank the following members for their questions, comments, answers and discussion on the NRC/DXAS Email list which were used in the preparation of this column: EWE Antenna: Thomas Giella, Patrick Martin; Sloper: Thomas Giella, Bruce Conti; DX-398 mod: Kevin Redding; Propagation: Thomas Giella, Chuck Hutton.
Please remember to keep sending me your questions or your suggestions for future topic-oriented columns to me either via the NRCDXAS listservs, by off-line email or by regular mail!