The Tarheel Screwdriver Antenna: one up on the Texas Bug Catcher

The veteran – The Trusty Texas Bug Catcher

I am not sure how it got it’s name, but if you have a Texas Bug Catcher antenna mounted mobile you are bound to pick up a few – bugs that is.  If you have an air coil then cleaning those bugs out of there could be a chore.

Much safer is to mount the Bug Catcher in a stationary location.  Yes, it is possible and I have gotten good results.  Perhaps it’s overlooked, but a Texas Bug Catcher makes a good portable antenna, limited-space antenna, and a good stealth antenna for those  communities where antennas are considered an eyesore. 

I been using a Bug catcher for more than a decade.  I first used it on a balcony bolted to a steel railing in a Chicago high rise on the 40’th floor – 400 ft up.  When I moved to a location on the ground I used it in the backyard and on camping trips. 

For portable or backyard use all you need is an 18 inch galvanizedpipedriven into the ground with a sledge  hammer.  Mount the Bug Catcher to the pipe using common mounting hardware you can find at a truck stop or Radio Shack that sells CB mounting hardware (3/8-24 stud)

The Catch to the Bug Catcher

If you take a look at the Bug Catcher you can see the pain points of this antenna – it has taps.  Yes, it’s “continuously tuneable”, you can set the taps any place you want.  But after you have the tap points set – that’s it – those are the taps points you use until you change them.

Pain Points = Tap Points

First, the tap points will be the only ones you can use  until you change them.  Second, finding the tap points can be painful.  Heaven help you if you don’t have an antenna analyzer.  It is going to be a long process of set-and-test until you find the tap points of the center points of the band portions that you want to work.

How it works – the principle

When you attach the clip to one of the taps it  “shorts out” all the windings below it.  So, you adjust the inductance of the coil by shorting out some number of windings with the lead which is attached to the base of the antenna.   The higher the tap on the coil ( from the bottom) the lower the inductance.  The lower the tap the more inductance. 

Since the Bug Catcher (about 10 ft tall) will be too short on most HF bands it will have a capacitive reactance and a high SWR.  To “tune out” that high SWR caused by the capacitive reactance you add a inductive reactance.  When the inductive reactive matches the capacitive reactance then you should have a pure resistive load.  You can think of the loading coil as an inductor in series with a capacitor.

So, the windings on the coil on the Bug Catcher provide you a (nearly) infinitely variable inductance for you to use to tune out (cancel) the capacitive reactance of the “too short” antenna.  All you need to do is find the place on the wire of the coil that gives you the inductance you need.  That’s where you attach the tap.  Easier said than done.

Read an excellent article by W8JI on Inductors and loading coils.

Finding the Tap Points

The antenna above is my Texas Bug Catcher.  To set this up I painfully analyzed the antenna at regular points on the coil windings to find the resonance point for various bands.  For example, from the top of the antenna:

At the 3 turn point the resonance is at 16.589 Mhz
At the 6 turn point the resonance is at 15.626 Mhz
At the 9 turn point the resonance is at 13.302 Mhz

So you ge the idea.  Right off you see that you will not be able to work 15 meters (21 Mhz) and above – the antenna is too long.  You also see that between 6 turns and 9 turns you will find a 20 meter resonance point.

Onward:
At 7.5 turns the resonance is 14.239 Mhz
So that’s one of my tap points.

How critical is the position of the tap point? 
At 7 turns the resonance is 14.99 Mhz and
At 8 turns the resonance is 13.870 Mhz.

Stop! – This is too painful.

Suffering builds character – so we will continue

At 26 turns is the resonance point for 7 Mhz ( 40 meters)

2 turns up from the bottom – 3.835 Mhz
4 turns up from the bottom – 3.90 Mhz
6 turns up from the bottom – 3.961 Mhz

On the antenna above, my tap points are for 20M, 40M, and two for 75 Meters.

Enter the Tarheel

From the suffering above, you can see why you need a screwdriver antenna. 

It was only my success with the Texas Bug Catcher that I decided to buy a Tarheel.  The Tarheel, which is generically a screwdriver antenna, mitigates almost all the pain points of the Texas BugCatcher.  The Tarheel is truely continuously tunable with the push of a button.  The mechanism in the Tarheel – or any screwdriver antenna for that matter – does what the taps do on the Bug Catcher – it shorts out part of the loading coil to produce a variable inductance that you use to tune out the capacitive reactance of your “too short” antenna.

Which Tarheel to buy

At the time of this writing (2009) there are 6 Tarheels to choose from

Little Tarheel II — 3.5 MHz-54.0 MHz, 200 watts PEP — 1 1/4″ coil — 16″ base — 32″ whip
Model 75 “Stubby” — 3.7 MHz-34.0 MHz, 250 watts PEP — 2″ coil — 16″ base — 6′ whip
Model 100 — 3.4 MHz-29.0 MHz, 1.5 Kw PEP — 2″ coil — 3′ base — 6′ whip
Model 200 — 3.4 MHz-28.0 MHz, 1.5 Kw PEP — 2″ coil — 4′ base — 6′ whip
Model 300 — 1.7 MHz-29.0 MHz, 250 watts PEP — 2″ coil — 3′ base — 6′ whip
Model 400 — 1.7 MHz-28.0 MHz, 250 watts PEP — 2″ coil — 4′ base — 6′ whip

If you want to run any kind of power then your only choice is the Model 100 or Model 200.  I picked the Model 100 since it has a shorter base ( 3 ft rather than 4 ft) and the fact the the claimed frequency coverage was into 29 Mhz.  This would let me work 75 meters all the way up into the 10 meter repeaters.  Sine I wanted to run my 800W Ameritron linear 1.5Kw power handling capability would do the trick.

Read our related article – Life on HF – The Age of Power

These are not inexpensive antennas.  One would think that the Little Tarheel would be much less money than the high power models.  Not so.  The Little Tarheel at $379 is only $10 less than the Model 100 at $389.  After discussing (at lenght) the pricing of these antennas with WB0W it seems all to make sense.  The cost is in the drive mechanism, the wire, and the machining – which is common to all of them.  Size does not matter.

Dealing with WBØW

WB0W, Inc. was founded by Gaylen Pearson (WBØW) in 1985.
Gaylen & Jean (KCØGB) attend approximately 44 Hamfest annually
As well as operate a full time mail order business
http://www.wb0w.com/tarheel/tarheel.htm

I have to say that dealing with Gaylen and Jean was one of the most pleasant experiences I have had with sellers in a long time.  I see them at hamfests from time to time and they are great people. 

You won’t find this on any of their web pages but they manufacture the Tarheel. When I wanted a particular model and color that they did not have in stock they told me they would make me one and send it out on the next day.  I also talked to a third person, seemed to me perhaps the guy who does the manufacturing, and he was able to answer all my technical questions and tell me something about the internal mechanism of antenna and drive mechanism. 

So, bottom line on WBØWis A++

My Tarheel Model 100

The Tarheel arrived in a few days.  In the large long box that arrives you will find the well-packed antenna base, the whip, and two boxes.  In one box is the control cable and the other box contains the control switch, silicon sealer, a matching coil, and other pieces of hardware.  I opted for the 50 ft cable replacing the shorter cable that came as part of the package and paid the delta on the price.

I attached the control cable, the up/down control switch, and 12 volts.  Gave it a shot.  All worked as advertised.  One observation is that there is no “stop/limit” at the top and bottom of the travel.  The motor just tries to keep turning the screw mechanism. 

It certainly would be a point of improvement to add an electrical stop or limit  at the top and bottom of travel to ensure one does not accidently burn out the motor.

Another thing I am sure I will discover is that the next option to buy is the control box that shows you the position of the antenna via a digital indicator.

Using the up/down switch you don’t know where the you are.  The optional control box provides a digital readout on the position of the shorting section on the loading coil.  This is an expensive option.

The benefit of the digital control box is that once you find the resonance point for a particular band and band segment you can go right to it.  Without the digital control box, having only the up/down switch, you will have to hunt and find it each time.  So, judge this convenience at about $100.

I have not yet placed my Tarheel 100 in service.  My expectation is that it will work as good, or better, than the Texas Bug Catcher that it will be replacing.  When I do get it set up and have some time to run it through its paces you will find a review on this site.

Resources

Note: The pictures near the top of this posting were taken from a various places on the web showing how other people have mounted their Tarheels.  I have used my Texas Bug Catcher in similar places as depicted in the photographs.

The Tarheel Antenna Home Page – http://www.tarheelantennas.com/
Tarheel installation photos – http://www.tarheelantennas.com/install_photos
WB0W Home Page – http://www.wb0w.com/
Read our related article – Life on HF – The Age of Power
Read an excellent article by W8JI on Inductors and loading coils
Check out the rest of this great site – http://w8ji.com/
Build your own Bug Catcher for $20
And one for your kids