The PT Boat Forum

Forum Category: PT Boats of WWII

Forum Name: PT Boats - General

Topic: What is this wheel on top of the deck house?



Posted By: Ray Wilbur | Posted on: Jan 9, 2010 - 8:59am
Total Posts: | Joined: Unregistered



Posted By: Ray Wilbur | Posted on: Jan 9, 2010 - 9:00am
Total Posts: | Joined: Unregistered

It appears to be the RDF antenna (Radio Direction Finder). It just looks a little different then the usual one we see in photos with a radius bullnose on the vertical shaft.

DIck . . .

Posted By: Dick | Posted on: Jan 9, 2010 - 1:06pm
Total Posts: 961 | Joined: Aug 27, 2006 - 6:36pm

It slightly resembles the one that was mounted on 77" Elco's, this one is smaller though, but it is mounted in the same general location.
Take care,

Posted By: TED WALTHER | Posted on: Jan 10, 2010 - 1:11pm
Total Posts: 2907 | Joined: Oct 16, 2006 - 7:42am

No No No. It is not a RDF antenna it is an IFF antenna. It goes to either the BN Unit or the BK/ABK Transcievers. These are two parts of the Identification Freind or Foe system which is configured to work in unison with the SOA Radar. There should be another similar, (but thicker wheel) "Ski Pole" or "Steering Wheel" dipole antennas up on the side of the mast as well. There is a good explanation of this in the Radar Operators Manual, in the section header about IFF on the HNSA website.


Here are some excerpts from the manual:

Either a "stove pipe" or a "steering wheel" antenna is used with these latter types, which are non-directional because they are merely single dipoles.

The BN is identical to the BL insofar as component parts and operational characteristics are concerned. The main differences between them are in size and power output. The BL is the larger, more powerful unit used with air-search radar on the larger ships; the BN answers the need for a compact, lower power unit that will operate on both large and small craft in conjunction with the surface-search radars, The BN is generally connected to the non-directional type of antenna.

Since the transpondor was originally designed for aircraft use only, the ABK-BK is small, compact equipment weighing about 30 pounds. Housed in the cabinet are two sections comprising the receiver and the transmitter. In its operation, the transpondor is entirely automatic once it has been turned on. Although it can tell a ship or ground station that the plane carrying it is friendly, it can not furnish the pilot of the plane carrying it the same information about the ships below him. Only the ship or land station finds out that it is a friendly airplane. The BK in your ship hookup is not associated in any way with your own radar equipment. The plane equipped with ABK may not have any other radar at all, but if it should have, it has no connection whatsoever with its IFF unit. The ABK, located in the plane, is connected to a small non-directional antenna which intercepts the questioning signals from any direction. An antenna with this characteristic of picking up signals sent out from any direction is very desirable, for the safety of the craft depends upon its ability to receive the challenges from all points of the compass and send back the answers which appear as the identifying pips on the scope of the search-radar indicator.

The steering wheel dipole antenna is generally used with BK in shipboard installations, and a single dipole is utilized for aircraft (ABK) installations.

Jerry Gilmartin

Posted By: Jerry Gilmartin | Posted on: Jan 11, 2010 - 2:00pm
Total Posts: 1244 | Joined: Oct 8, 2006 - 11:16pm

O.K. the ski poles you mention were on the SO-A radar mast, I know some boats in the Med (RON 29) carried two one on each side of the mast. But I don't ever remember noticing a small one like this, And I even have this photo of 157! Oh Well.

Posted By: TED WALTHER | Posted on: Jan 11, 2010 - 5:25pm
Total Posts: 2907 | Joined: Oct 16, 2006 - 7:42am

Hi Ted,
Yes the other thing that I noticed was that even the Italieri Model of PT596 includes this IFF antenna in the same exact position on the top of the charthouse next to the Starboard Nav light. I know a lot of RON15 and RON22 Higgins Boats in the Med had 2 IFF antennas on their masts, but I always have noticed the 80 foot Elco boats separated them out, with one on the chart house and the other on the mast. I am not sure how important this is to separate them, but it seems to have been pretty common. Jerry

Jerry Gilmartin

Posted By: Jerry Gilmartin | Posted on: Jan 11, 2010 - 5:58pm
Total Posts: 1244 | Joined: Oct 8, 2006 - 11:16pm