Railfan Technology > Cushcraft ARX-2 antenna RR band tuning.

Tuning the Cushcraft ARX-2 "Ringo Ranger" base outside
vertical antenna for operation centered at the middle
of the US RR band at 160.89 MHz:

Note: These instructions and dimensions do not apply to the
Cushcraft ARX-2B. The ARX-2B antenna is a different design.

Download the Cushcraft ARX-2 PDF manual and print page 5.

http://www.cushcraftamateur.com/support.php?productid=ARX-2

Modify the dimensions so:

A = 50 5/8"

B = 40 7/8"

Note A and B dimensions are from the upper and lower edges
of the insulator for phasing hairpin section C.

C = 8 1/8"

Note that dimension C is from the outer edge of tube A, not the middle
of the screw heads as in the inset drawing for the ARX-450.

Tuning rod placement. Take a piece of masking tape 8 1/2" long and
beginning at the center of nut 11 on the left side of Figure 1 which
holds the tuning loop to the bracket for the coaxial connector, run
the masking tape around the outside of the tuning loop and tighten
the screw on clamp 67 with the end of the masking tape at the center
of the screw. This will position the tuning rod properly.
Remove the masking tape before use.

Modifications:
These may offer a slight improvement in performance and are useful
if a non-conducting mast is used. These modifications serve to help
clean up the pattern of the antenna by reducing currents flowing on
the outside of the coaxial cable.

The end of the coaxial cable right at the connector should have a
3" loop with 2 turns. Hold in place with black zip ties or a good
grade of black electrical tape. If you use zip ties, put a turn of
black electrical tape over the zip ties to help protect them from
UV light damage.

Crimp and/or solder a 18" piece of solid or stranded 16 or 14 gauge
insulated copper wire to a terminal lug having a 1/4" hole. Put a
1/4-20 stainless steel nut on screw 47 to act as a locknut. Run the
nut all the way to the head of the screw. Install the terminal lug
with the 18" section of wire next to the nut. Orient the lug so the
flat surface faces the mount,then install a stainless steel lockwasher.
The preferred lockwasher for this purpose is a stainless steel
inside tooth star-format lockwasher although you can use an external
tooth star-format stainless steel lockwasher or a stainless steel
split ring lockwasher. The lockwasher and locknut MUST be made from
stainless steel. The important thing is to have no lug-to-aluminum
metallic contact between the terminal lug and the aluminum mount section.
After tightening down screw 47 to the mast, run the locknut down
towards the mount and snug it against the lockwasher.
Insulate the non-terminal end of the wire so it does not touch the
mast. Hold in place with zip ties or black electrical tape.

Using instrumentation, I was able to get the VSWR to less than
1.1:1 over the US RR band. The dimensions mentioned are the
ones used to tune the antenna.

I'll be happy to answer any questions regarding this work.

Be Well,

Tim Colbert K3HX




.



Edited 1 time(s). Last edit at 06/09/17 10:12 by K3HX.

I have a 30 year old version of this antenna. A storm brought it down once and bent it slightly. If anyone is considering an antenna to mount outside, this a an excellent antenna.

John

Very good antenna for the money. We use this at one of our repeater locations and knock on wood it has been a very reliable antenna. KJ4PIU

Great idea, Tim.

It's always fun to re-purpose surplus materials to build great performing antennas for RR listening. We have an EMT boom with 8 copper ground wire element Yagi still going strong after 34 years. Just upgraded the coax to EtherNet distribution cable (similar to RG-8) and now works better than ever. At one time in NorCal we had two horizontally stacked 16-element Yagis with boom made of Aluminum irrigation pipe with Aluminum welding rod elements. Man what great reception ! Heard Klamath Falls yard, Western Pacific dispatch, trains in Mount Shasta, and all sorts of other RR traffic in the Sacto Valley from Redding, CA.

Guess we'll have to get those working again....