AS-2109 Antenna


AB-1036 Base	AB-1037 Spring	AS-2125 Antenna

General Description

The AS-2109/PRC (nsn 5985-00-087-1146) is intended for use on the PRC-25 and PRC-77 VHF Low Band Squad Radios. This antenna can be used in two ways: (1) with the telescoping whip collapsed or with the whip extended. This antenna appears in the PRC-77 parts manual TM 11-5820-667-20P but when I asked about it many people told me that it was never fielded. Apparently a pilot run was made and something caused the military to not go forward.
The outer wrapping paper has contract number DAAB07-76-C-0191 and the date "C-3/82".
TM 11-5820-667-20P shows the AS-2109 as part of the radio set PRC-77 in addition to the AT-892 tape antenna and it's gooseneck base P/O AT-892 and the AT-271 fishing pole antenna and it's AB-891 spring base. This is consistent with the idea that this antenna was not fielded to replace the two other antennas, although that is clearly it's function.

There are no matching elements in the antenna so it could be used at any frequency where there was a way to match it, like in the HF band. My TWA2 Antenna Adapter will accept the 5/16-24 male threads on each of the component parts of the AS-2109 and supply a male 3/8-24 as used on ham, CB, commercial antenna bases.

It is composed of three parts:

AB-1036/PRC Base

The base has a 5/16-24 male thread to mate with the radio and has a 5/16-24 female thread that accepts the Spring. It also has a retractable pin to activate the switch in the radios that indicates whether the short or the long RF matching should be used. It also has a three position (-90, 0, +90 degree) hinge so that the radio can be used in a horizontal or vertical position and have the antenna pointing up. It also has a 360 degree rotation after the threads have seated. This allows the 3 position hinge to be located so that it will hinge toward up rather than hinge toward the side. The length of the base is about 3.75".
The knob that activates the pin to tell the radio which matching circuit to use is marked "3 UP (CCW arrow)" meaning raise the pin when in the 3 foot mode and "(CW arrow) 10 DOWN" meaning to lower the pin when the antenna is in the 10 foot configuration. I think this is the weak point of the antenna. It would v be very easy to extend the antenna and forget to change the knob or lower the antenna and forget to change the knob. In either case the radio would have low radiated power and maybe even damage the radio.

AB-1037/PRC Spring

The bottom has a 5/16-24 male thread to go into the Base and the top has a 5/16-24 female thread to accept the telescoping antenna. The spring is made in two parts the lower spring is about 4.5" long and the upper solid part is about 8.5" long for a total length of 13". I think the solid part is needed so that when the whip is attached in the collapsed configuration the overall length of the three parts will be the same as when the tape whip is used on the radio. This implies that the telescoping whip was a preexisting part and may be available separately?
AS-2125/PRC Antenna Element

This is a 7 section telescoping antenna that is 19" long when collapsed and 8' 7.5" (103.5") long extended. The bottom has a 5/16-24 male thread to go into the spring. The antenna is nomenclature "AS", I think this means Antenna System and may be part of other antenna systems.

What Happened

Accession Number : AD0829873
Title : ANTENNA AS-2109/PRC (ACL 17/67M).
Descriptive Note : Letter Report of Evaluation, Apr-Nov 67,
Corporate Author : ARMY CONCEPT TEAM IN VIETNAM APO SAN FRANCISCO 96384
Personal Author(s) : Murga, Jesse A.
Report Date : 30 MAR 1968
Pagination or Media Count : 10
Abstract : The AS-2109/PRC is a telescoping whip antenna considered as an item to replace the AT-271 and AT-892 antennas currently being used with the AN/PRC-25 radio. It was evaluated by three units and the major drawback was the rigidity of the antenna sections which impeded movement in confined areas or through heavy foliage. (Author)

Descriptors : (*ANTENNAS, RADIO EQUIPMENT), PORTABLE EQUIPMENT, EXTENDABLE STRUCTURES, PERFORMANCE(ENGINEERING), JUNGLES, TROPICAL TESTS.
Subject Categories : ELECTRICAL AND ELECTRONIC EQUIPMENT
Distribution Statement : APPROVED FOR PUBLIC RELEASE

Thanks to Scott W. for finding this.

Configurations

Note: It's important to set the base extension probe to match the length. If this is not done damage to your radio may result.

Short 3'
With the 3.75" base + the 13" spring + the 19" collapsed whip = 35.75" or very close to the 35.5" for the AT-892 tape whip with the gooseneck base.
Long 10'
The 3.75" base + 13" spring + 8' 7.5" extended antenna = 120.25" which is a few inches longer than the 117.5" for the AT-271 fishing pole antenna on the AB-591 base.
Lengths of some antennas can be seen on my Tape Whip Adapter web page.

Applicable

PRC-25 - be sure to set base probe to match antenna length
PRC-77 - be sure to set base probe to match antenna length

Not Applicable

Do Not Use this antenna with the:

PRC-117 (RF3090) can only be used when the Harris antenna adapter is used and then only when fully extended. But is the base probe is extended it may damage the microswitch on the radio. Best to not use it at all.

PRC-104 the threads don't match, but even if my TWA adapter was used, the antenna tuner might not like it?

Links

eBay Seller gdix2 has these listed as PRC-25/77-70-104-117 Radio Antenna with AS2109/PRC in the text.

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