Antennas

General Information

The antenna used for either receiving or transmitting is a vital element in the communication link.  In most cases the antenna has a great deal to do with how well the receiver or transmitter works.

Antennas are reciprocal, meaning that an antenna designed for transmitting will work for receiving.  A passive receiving antenna will also work for transmitting.  BUT the goals are different for reception and transmission.  In general a receiving antenna should provide a good signal to noise ratio.  In general a transmitting antenna should radiate energy as efficiently as possible.  A loop may make a great receiving antenna for a broadcast band radio but would be terrible as a transmitting antenna.

For antenna theory see my electronics page and some linked patents.  For Propagation see HF Propagation page.

VLF Antennas

McKay Dymec DA-100 Active Whip - Board Layout & Circuit Diagram - through 30 MHz coverage
McKay Dymec DA7 Loop
AMRAD - Active Low Frequency Antenna has coverage to 30 MHz
AS-2108/ARN-89 crossed active loops for chopper radio direction finding
Light Weight Beacon - a 50 foot tall antenna system that fits in a back back along with a transmitter
Home Brew Loopstick for WWVB - work in progress, not working yet

HF Antennas

Dipoles & Wires

The B&W Broadband Folded Dipole Antennas (ASW-90) U.S. Patent 4423423  is an excellent receiving antenna for broad band signals like chirp sounders.  This design is also called a T2FD.  The efficiency for transmission goes down rapidly below 40 meters.
AS-2259 or AS-2268 (Collins 637K) NVIS tatical antenna
GRA-50 1.5 to 20 Mhz Reel dipole where the reels are at the far ends, not the center.
GRA-4 is a  two mast system for erecting various wire antennas (TM 11-2651, TM 11-5985-249-24P)
GRA-12 is a  three mast system for erecting various wire antennas (TM 11-2651, TM 11-5985-249-24P)

The GRA-4 and GRA-12 are similar to the GRA-50 except the GRA-50 has no masts.
The 40' Mast, Support System for Camofloge may be used for wire antenna support if the Aluminum version is used, the fiberglass version may not be strong enough.

AS-1321/PRC-47 Antenna 45 foot long wire
AT-984/G 150 foot wire
SORAK - both H.F. and VHF low band wire antennas OE-452 - NSN 5985-01-279-7942, Special Operations Radio Antenna Kit
Hy-Gain HA-4000, 18TD, Collins TD-1, 637T-2 - a dipole made with two steel tape measures as the center part.  You pull out the tapes, marked in the metric system and you're good to go


637T-2 has two reels with antenna wire on each.  Center support hole on top and type N(f) connector on the bottom.  Used to quickly and easily make a dipole for NVIS ops.

Inverted L

The Inverted L antenna was used at least up into the 1970s and probably even today.

In the 1970's I met Art W6TYP, now a silent key, who was a very big fan of long wave and 160 meter AM operation who used the Inverted L antenna.  Quite a character who would phone you at 3 am to let you know of some unique propagation so that you could listen.  His apartment walls were deep yellow from nicotine stains.

During the Vietnam era there were articles written about how to use H.F. radio for communications where the range was zero to a few hundred km or miles (for this either unit is close enough).  At this time it was given the name Near Vertical Incidence Skywave (NVIS).  The idea being to beam the signal straight up, let it hit the ionosphere and then bounce back down.  The frequency needs to be chosen properly, too high (say above 12 MHz) and the signal keeps going up and never comes back.  Too low the the D layer absorbs all of it.

The antenna for NVIS should be a horizontal wire ideally 1/4 wave above ground, but works with less efficiency and it gets closer to the ground, just like the horizontal part of an inverted L antenna.  Very few hams can put up a horizontal wire at 1/4 wave on 160 meters (i.e. 40 meters or about 120 feet) or 80 meters (i.e. about 60 feet) but instead put it up about 30 feet.

For working DX you don't want to use NVIS mode, but rather need a vertical antenna, ideally 1/4 wave tall with a good ground system.  Again not very practical on 160 or 80 meters.  A good compromise is to use a shorter vertical with top loading (sort of like an umbrella), but again that's difficult to manage.  A practical way is to run the antenna from a ground floor window up to the top of a chimney or pole then make the top hat by running the wire horizontally.

So the Inverted L antenna provides both close in coverage as well as DX from a single wire antenna.

Whips

AS-1320/PRC-47 Antenna 15 foot whip
GRC-106 15 foot whip -photo - in CW-206 bag - Fair was selling these as a GRA-50, but they are for some transmitting application because of the insulating sleeve for the lower whip (ms-11x whip sections.  Not the receive only antenna for the R-442.)
AT-271 Fishing Pole 3 meter
AT-1011 Shakespeare 120 HF antenna system 12, 16 or 32 foot whip



M-442 Adapter - Accepts AB-21 or MS-116 tubular antenna elements and has common 3/8-24 male thread to fit the PRC-104, AB-591, etc.

got this one from Fair Radio








 
Tape Whip Adapter - Accepts 5/16-24 male thread on mil antennas and screws into 3/8-24 ham, CB, commercial antenna bases.  The 5/16-24 female thread is deep enough to allow the AB-591 spring antenna base to be used.



Ship's Goniometer NUS-883 - photo - Adcock array for mounting on ship's mast unknown frequency

PRC-174

The PRC-174 and PRC-174S are radios that have a strong similarity to the PRC-104.  But instead of mounting the antenna at right angles to the front panel like on the PRC-25, PRC-77 and PRC-104, they use a bracket on the side of the radio ( MT-3613 PRC-174 Antenna Bracket).  Some how this allows the antenna to be pointed up when the radio is laying flat or when the radio is being carried in a pack frame.  The antenna mount must be made from unobtanium.

The photo at left shows a modified AB-1135 (painted OD) attached to the PRC-174 with the AS-2109 antenna.

The AB-1135 (see below and on PRC-25 web page) is a stack intended to be driven into the ground.  But it can be modified to fit the PRC-174 to replace the antenna bracket.  This came from:
" OLDBUZZARDRICH ", W2OBR, Richard A. Decker

21 Feb 2008 - eBay seller 4x6mu is offering an antenna bracket that he made and it includes a magnet that changes the internal matching.

"This Side Antenna Mount is workshop made to fit the TADIRAN RT-936\PRC-174 2-30MHz HF Manpack Radio.

The Mount includes a magnet to trip the magnetic Antenna switch to choose side antenna from Front BNC Dipole Antenna connection. Includes also two fitting mounting screws to fit the PRC-174 side."
It's not clear if this is just a switch that selects the antenna connection or if it includes different matching?

VHF Low Band Antennas

Mast Mounted

OE-303 1/2 Rhombic

OE-254 Bi-Conical

RC-292 1/4 Wave Vertical

Create Discone - this makes a great scanner receive antenna when a Radio Shack 15-1170 amplifier is used.

Create Log Periodic

AS-2851 LPA (HY-GAIN LP-1402AB) Hor or Vert polarization can be changed from the ground.

AB-1135

AB-1135 is a stake with the antenna socket from a PRC-25 mounted on top and with a BNC-f connector. eBay store Military Surplus Junk run by  Jim Williams & Sons eBay seller j5w23 Rear 330 Main Street, Dickson City, PA 18519, USA  1 717-383-1295. Also see my PRC-25 page for more about how to use with VHF lo band radios.

Mobile Mounts

AS-1729 Remote tuned vertical dipole.  This is the antenna system using the MX-6707 and works with the VRC-12 series radios as well as with the AM-2060 and PRC-25 or PRC-77.

Hand Held

AT-784/PRC directional Loop
Rubber Duck - used on PRC-68 family of Squad Radios (Note: this antenna has 30 dB less radiated power than the AT-892 1 meter tape whip on a PRC-68!, that's NOT a typo)
AT-892 1 meter Tape - used on PRC-68 family of Squad Radios
68AA Antenna Adapter - fits the special PRC-68 family of hand held squad radios and has a standard BNC(f) connector plus a DC return to the more modern radios in the family will correctly know an external 50 Ohm antenna is connected.

Man Pack Radio Mounted

AT-271 3 meter fishing pole used with the AB-591 spring base
AS-2109 Telescoping that can act as either a 1 meter or 3 meter antenna for the PRC-25, PRC-77 etc.

Field

AT-984/G 150 foot wire
SORAK - both H.F. and VHF low band wire antennas

VHF High Band Antennas

Eggbeater - has a circularly polarized pattern going up which is good for working satellites and has vertical polarization in the direction of the horizon which is good for working most VHF stations. See Brooke's Military Information/Equipment  for more on this one.

FM Radio - FM stations can use horizontal polarization to reach receivers in stationary locations with indoor or outdoor antennas.  They can also use vertical polarization to reach automobile whip antennas.  Most stations divide their power between the two depending on their target audience, commuters, at work, commercial use, etc.  A vertical antenna may work better at your home if the station you want to hear is targeting commuters.

Radio Shack

UHF Antennas

This is the military 200 (or 225) to 400 MHz band used by aircraft in the AM mode, for Line Of Sight coms by ground troops, and used for linking to satellites.

AS-390A/SRC has ground radials for pole mounting and painted navy grey, like for a ship or control tower.
AS-1405/PRC-41 Log Periodic
AT-803/VR has same antenna element as AS-390A/SRC but is intended for mounting to a metal shelter roof (OD paint).  mentioned in FM 24-24 as part of the VRC-24 & TRC-68 systems described in TM 11-5820-222-20.

DM CN18-11/A-2 Combined UHF (225 - 400+ MHz) and L-band (950 - 1220 MHz).  The latter band includes:

TACAN - 962-1213
DME - 1215
IFF - 1030 & 1090 Mhz
Data Link - AN/AXQ-14 Data Link System (GBU-15 or AGM-130)  ??? Freq.  Link-16 JTIDS ???
Used on  F15
The literature calls it an "Integral Diplexer" type.  The other type has a single type-Nf connector.  The implication is that the antenna proper covers both 225 -400 AND 950-1220 MHz.  But built-in diplexer seperates 225-400 from  the 950-1220 Mhz.  Since the L-band power is specified as 16 W average, 4 kW pk I'm guessing J2 the larger connector is rated for high power and the TNCm is the UHF connector.

Microwave

Satellite

When it was discovered that the cable companies were getting their programming by means of C-band (3.7 to 4.2 GHz downlink) receivers there was a move to make home brew systems.  The cost of a parabolic dish goes up as some power of the diameter.  The cost of a low noise amplifier goes up as some function of how low its noise figure is.  When the sum of the antenna cost and the low noise amplifier cost are plotted the curve has a sweet spot.  Over time the sweet spot has moved in the direction of smaller diameter antennas and better low noise amplifiers.

The best F/D (focal length of the antenna divided by it's diameter) for a parabolic antenna to have maximum gain is about 0.45, so most TVRO antennas were built with this rather flat shape.  The best G/T (gain divided by noise) is at an F/D of 0.3.  This is really the key specification since what the receiver wants is the best possible G/T.  I got one of the antennas from Stanford used for a study of the Sun (they had 16 in a N-S line and 16 in an E-W line all phase matched feeding a common receiver and all driven in hour angle to track the Sun.  These were spun Aluminum with an F/D of 0.3.  The feed was modified by an engineer working at Lockheed in Sunnyvale (government satellites) from a classical horn feed to what I call a nozzle feed that had matched E and H plane radiation.  This antenna out performed many commercial units with diameters up to 16 feet.  It used a WR-284 waveguide "button Hook" feed rather than use rods to support another type of feed.  It had only one polarization.

At first all the TVRO satellites used Vertical polarization.  Soon someone figured out that they could get twice as many satellites in the same angular space if they polarization alternated from horizontal to vertical.  The cross polarized signal is down 20 or more dB depending on the quality of the antenna systems.  Today this is still done on the Ku band TVRO 18 inch dishes.  It's too bad that they did not change over to circular polarization for the Ku band systems.  That would make VSAT type uplinks much easier to do since the "cross pol" adjustment would go away.

Starband Vsat antennas.  The top one is for the new (2006) Nova system where the indoor box is a stand alone unit which has a CAT5 cable to the computer (no software needed on the computer).  The lower dish is left over from the Starband 360 system.  The 360 required Starband software on your computer, not a good thing.  In the background you can see the OE-254.

Motorola Timing GPS receiver above McKay Dymec DA-100 active whip.
The output from the GPS antenna goes to a 4-way splitter.

The cable on the right it going up to a Radio Shack scanner antenna.

Radar Warning Receiver

I worked on some of the microwave parts used in these systems.  They used four cavity backed spiral antennas on each corner of an aircraft, each feeding a multicoupler with 3 or 4 outputs, each exclusively covering a different radar threat frequency and on each of these outputs was a Limiter-Detector that I designed and oversaw the production of. 

Direction Finding

There are a number of ways to get a bearing to a signal:
Doppler - uses a rotating antenna element and measures the doppler shift
Pseudo Doppler - switches antenna elements to simulate a doppler - BM Engineering out of business 1998-
patent 4475106 "High sensitivity portable radio direction finder"
Goinonmeter - rotating central comutator with multiple directional antennas like in the Wullenweber (Elephant Cage).
Amateur Radio Direction Finding Web Ring -
IDA stands for Information Dense Antenna - Roger Karlsson - 6407702  Method and system for obtaining direction of an electromagnetic wave
Loop antennas have a sharp null that can be used to get a bearing that's either to or from the station.  An Adcock arrangement of verticals also has this null property.

For navigation a DF antenna can take some time, like a manually turned loop, to find the bearing to the transmitter.  But for ELINT (Electronic Intelligence) the DF system needs to instantly have a bearing on a signal of short duration (milli seconds).  The Wullenweber Antenna is an example of an ELINT type DF antenna.

OE4 - TM 11-5985-360-10 0.5 MHz to 1050 MHz

Receiving Loops

ARN-83 LF aircraft DF set
ARN-89 LF aircraft DF set
AT-339 VHF low band hand held DF loop for PRC-6, photo
AT-784/PRC directional Loop for use with PRC-25
DU-1 Loop Ant and CRR-50001 Coupler Unit - AAF Radio DU-1 page - Photo of DU-1 installed in OS-2U in movie Overboard when the kids are hiding at the dining table there's a DU-1 loop in the background for the next few scenes.
MN-24C manual rotation aircraft loop - photo of loop, flex cable & Control box - used with ARN-11 24 V Radio Compass, C-177/ARA-10, C-135, C-136, MN-28 Control Box, IN-4D Left-Right meter, MN-26LB receiver, MN-40D azimuth indicator,
PRD-1 HF DF set
Radio Receiving Set AN/TRQ-23 and Antenna Group  OE-4 DF set with up to 150 RPM loop rotation
URM-6 Field Strength set 14 to 250 kHz

Other DF

Time Delay Beam Steering - see below for antenna system for Rx & Tx to a azimuth & elevation
Goniometer - This is a Watson Watt (Adcock) array of 4 vertical dipole antennas designed for use on a ship. Photo
Antenna
Goniometer
NUS-883   Serial 54-8
Federal Electric
Manufacturing, Co. Ltd.
Montrael, Canada It is made to go on top of a mast with a 2" O.D.
It has 4 each vertical dipoles 50" end to end that are in a square pattern 14" on a side.
A Type-N connector and a male 10-pin military connector.
There is a lamp at the top that I think is a 110 Volt unit.
 I am looking for more information about this Goniometer email Brooke

Antenna Theory

This is on my Electronics web page.

Antenna Related

Pre-Amplifiers

When working at VHF and above frequencies the loss in the lead in coax becomes high.  There is a world of difference when a pre-amplifier is placed right at the antenna so the system noise figure is established at the preamp, rather than have the coax loss be added to the receive noise figure.  The Radio Shack 15-1170 works very well for this application.  Some of the other Radio Shack antenna amplifiers may cost more, but they are not continuous frequency coverage units like the 15-1170 MHz that work for a very wide frequency range

Antenna Tuners

This is a device that is connected between a transmitter and the feed line going to the antenna.  Typically there are coax connectors for in and out.  The military called them line flatners.  They transform whatever impedance that is seen looking into the feed line into 50 Ohms to provide the transmitter a good match.  The problem is that a high VSWR on the feed line results in a lot of signal loss.  These are rarity used for military applications.

Antenna Couplers

This is a tuner that is placed at the base of the antenna.  It has a coax feed to the remotely located transmitter and a high voltage insulator to connect directly to the base of the antenna.  An example would be the SGC - SG-231 Smartuner®.  You will see these used for military HF radios that are man portable, on land, sea and airborne platforms.  There needs to be a remote control capability or built in intelligence to control how the coupler tunes the antenna.

Some of these antenna couplers use vacuum relays or motorized vacuum capacitors or roller inductors in their design.  All of these are very high Q devices and so the power loss in the coupler is minimized.  Other antenna couplers use fixed inductors and capacitors and switch them using relays.  This type of coupler has higher losses than the larger higher Q military type.

Other antenna couplers are on my NRD 545 page

Antenna multicouplers

When you want to connect a number of receivers to a common antenna there is a very noticeable signal loss if you connect them all in parallel.  Instead what is needed is an antenna multicoupler.  They come as passive and active types.  There a number of government agencies that use these.  Some of the military Antenna multicouplers are on my NRD 545 web page.  I use the Stridsberg Engineering  MCA104 amplifier HF 4 output unit, it is hand sized rather than a rack sized military unit and has good specs and most importantly it works very well.  It's powered by a 12 Volt wall wart, but could be powered from a vehicle DC system.  It's driving my NRD-545, RCS-5A chirpsounder, McKay Dymec DR-33 receiver and Agilent 4395A spectrum analyzer.

A home brew 4-way GPS multicoupler based on Radio Shack satellite TV components

Duplexer

When a single antenna is to be used with two transmitters or transceivers a duplexer is used.  It contains two cavity notch filters. The filter connected to radio #1 is tuned to notch out the transmissions from radio #2 and vice versa.  These are used at most frequencies from HF and up.  CU-2194 is a VHF Low Band unit that gets it power from the transmitted signals so does not need any batteries.

Time Delay Beam Steering

The "Beam and null switch step steerable antenna system" U.S. patent - 4063250 by Richard C. Fenwick is a great explanation of time delay beam steering.  The "phased array" antenna is a special case of the time delay steered antenna.  Note that in the time delay steered array the direction of the maximum lobe is frequency independent whereas in the phased array it is a direct function of frequency.  Fenwick also patented a "Three band monopole antenna" 4145693 that was sold with the beam steering network by "Omega-T".

Patents

The US patent office is full of antenna related patents.  I have found that there are some great ideas that have never made it into text books, maybe because of the patent protection.  My Electronics page Antenna section has a number of patent links.  The US patent office has greatly improved in the last couple of years and now has ALL patents on line.  Prior to some year they are only available as images so are only accessible by patent number or class.

Links

Shortened Antennas for Portables by Dennis Starks
Army Mars - antenna page
Pneumatic Antenna Launching Systems - PVC fittings (similar to a spud gun) - I'm looking because when I use the sling shot and pull back the length of my arm it still will not go over the top of a 100 foot high tree.  - Antenna Launcher Modelling - help with understanding valves and barrel length.

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