clandestine antennas for amateur radio

NCDXC June 08NCDXC June 08 Page 1 of 46 of 46 AE6RR – Clandestine AntennasAE6RR – Clandestine Antennas

Clandestine AntennasClandestine Antennasfor Amateur Radiofor Amateur Radio

By By

Craig Bradley, AE6RRCraig Bradley, AE6RR

-••• -•-- •--• •-• --- •••• •• •- •••“BY PROHIAS”

NCDXC June 08NCDXC June 08 AE6RR – Clandestine AntennasAE6RR – Clandestine Antennas Page 2 of 46 of 46

BackgroundBackground• First licensed as WV6SVW & WA6SVW

– 1961 to 1967– No antenna restrictions (except parents)– Life was good

• Relicensed in 2004 as AE6RR– Main residence had minimal lot lines and CC&Rs– Vacation home in Truckee had CC&Rs but a large lot

with some tall pine trees– Antenna prospects did not look good– XYL thought that I had lost my marbles

• I was climbing up in the attic, on the roof, staring at trees


This PresentationThis Presentation

• Clandestine vs. Stealth antennas• What makes an antenna work• Multiband antennas• Possible locations• How well do they work?• RFI• QRO• Reference Material


Clandestine vs. Stealth Clandestine vs. Stealth AntennasAntennas

What is the difference?What is the difference?


Stealth AntennasStealth Antennas

• There have been many talks, books and articles on Stealth Antennas

• They are “Hard to See”• Construction varies

– Thin wire antennas in plain view– Towers and beams painted in camouflage colors

• Scheme is to blend with the background and minimize visual impact

• The antenna concepts in this talk can also be used to construct Stealth Antennas and others


Clandestine AntennasClandestine Antennas• Clandestine means “Hidden”

– Should not be visible to someone that may be looking for it

– May be hidden in plain sight (looks like something else)

• Flag pole, rain gutter, fence, etc.– May be hidden in or on a structure

• On top of roof• Attic, indoors, shed, etc.

– If you have CC&Rs• Clandestine antennas will not need to be explained• Stealth antennas may be discovered

– Once discovered, you will be a suspect• Increased surveillance may result


What Makes Antennas What Makes Antennas Work?Work?

Get the RF in the AirGet the RF in the Air


Some Antenna BasicsSome Antenna Basics

• Most of the RF is radiated from the high current portions of the antenna

• The highest current is where the impedance is the lowest– At the feed point

• The lowest current is where the impedance is the highest– At the end points– The ends have the highest voltage

• The end points don’t radiate much RF– They do contribute to the tuning of the antenna– They act as “capacity hats”


Bent AntennasBent Antennas

• If you don’t have space for an antenna why not bend the ends around?– You can get a lower frequency antenna in a

much shorter space – The ends don’t radiate much RF so it doesn’t

matter where there are pointed– The ends do have high voltage present so be

sure to insulate them well


Bent Antenna ExampleBent Antenna Example

• Conventional wisdom says that you can’t bend an antenna back on it's self

• SteppIR does not agree…


Antenna TunersAntenna Tuners• Antenna Tuner is a misnomer

– It does not “tune” the antenna– It is an impedance matching device

• Modern transceivers and amplifiers are designed to match a 50 ohm load– If the antenna is not 50 ohms you will have a miss-

match (high SWR)– Most solid state transceivers will start to limit the

output power if the SWR is higher than 2:1• A tuner will make your antenna “look like” 50

ohms to your radio– You will get full power out


A Word on SWRA Word on SWR• The Voltage Standing Wave Ratio (or just SWR)

is the ratio of the maximum and minimum voltages on the transmission line

• It is caused by the interaction of the forward and reflected voltages on the line

• If your antenna and transmission line impedance matches your transceiver output impedance there will be no reflections

• If the impedances do not match there will be reflections on the line

• SWR is not a measure of how well an antenna radiates– Dummy loads have an SWR of 1:1 …


Reflected PowerReflected Power• Gooch’s Paradox “RF Gotta Go Somewhere”

– Stealth Amateur Radio by Kleinschmidt

• It will “bounce” back and forth on the transmission line until it goes somewhere

• It can be radiated as RF by the antenna (good)• It can be radiated as heat by the transmission line (bad)• It can be radiated from your station “ground” (bad)• It can be radiated from your microphone (burned lips)• It can go into your home electronics (bad)• It can go back into your transceiver and cause it to limit

output power or cause heating or damage (bad)


A Word on Transmission LinesA Word on Transmission Lines• Transmission lines have losses

– Usually rated as dB per 100 ft with an SWR of 1:1– The losses are much higher at high SWRs

• Reducing Loss– Place the antenna tuner as close to the antenna as

possible (lowest loss)– Use balanced line between the tuner and the antenna– Use low loss coax to feed the antenna (LMR-400 or

9913)

• If you don’t lose power in the coax you have a better chance if it “getting out”


Transmission Line LossTransmission Line LossThe following table is for 100 ft of transmission line with an antenna

impedance of 1000 Ohms non-reactive at 14 MHz (Source TLW program by N6BV)

Type of line SWR at Load

SWR at Input

Total Line Loss

RG-8X 19.91 5.24 6.0 dB

Beldon 9913 20.33 10.01 3.043 dB

450-Ohm 2.47 2.41 0.137 dB

450-Ohm w/ 20 Ohm load

20.25 16.46 0.934 dB


Unbalanced AntennasUnbalanced Antennas

• Verticals or Long Wires

• Require radials (more stuff to hide) or a good ground (hard to do)

• May result in “RF in the shack” with bad grounds

• May “stick up in the air” – harder to hide

• You can “tune” the ground system but now you have created a balanced antenna…


Balanced AntennasBalanced Antennas• Dipoles, Doublets, G5RVs, Loops etc.

• No ground or radials required

• Less chance of “RF in the shack”

• Simple low cost construction - usually wire

• Can be bent around to fit the space

• Keep most of the radiation at the antenna


Loaded AntennasLoaded Antennas• Loading coils can physically shorten an antenna• Highest current is between the feed point and

the coil and the lowest current is after the coil• Maximum radiation will be from the portion

between the feed point and the coil – Maximize the length of this part

• Loaded antennas are more complicated to tune– Nearby objects will interact

• If you want to get on 80M, you may need to consider a loaded antenna if space is limited– RFI noise may be a big problem here


Loop AntennasLoop Antennas• Loop antennas can fit in many places• Outdoors may be hard to support it and keep it

concealed• Indoor horizontal loops can run around the top of

your room or around the attic• Small loops can be vertical and indoors• There are several companies that sell loops and

many construction articles• You may need a special loop tuner• Many Hams have had good results with them


Multiband AntennasMultiband Antennas

Want to get on more than one Want to get on more than one band?band?


Required EquipmentRequired Equipment• If you want to operate on multiple bands with a simple

antenna you will need an external Antenna Tuner– Most internal tuners will only match an SWR of 3:1 or less– You will need a good external tuner– Auto Tuner preferred

• You can easily get a simple antenna such as a dipole to resonate on a single frequency– With a tuner, it will load on many bands (higher frequency)

• Multiband antennas– Can be complex– Are very difficult to get working close to other metal objects– Clandestine antennas will likely be near many unknown objects– Will probably have a high SWR on some bands


Types of Multiband AntennasTypes of Multiband Antennas

• Trapped Verticals– We already talked about verticals

• Horizontal Balanced Wire Antennas– Fan or parallel dipoles– Trapped dipoles– Doublets– G5RVs


Possible LocationsPossible Locations

Time to use your imaginationTime to use your imagination


IndoorsIndoors• Can be done but should be your last choice

– Limited space will require very compact antennas– Loops and bent wire antennas for the higher bands

may be possible– Small current loop antennas may be usable

• RFI will be a problem (Transmit & Receive)• RF exposure to you and your family will be higher

– QRP may be required• The XYL may not consider your creation

“decorative”– You won’t see indoor antennas on HGTV or in home

decorating magazines


AtticAttic• If you have an attic that you can get into this

may be a good possibility• Large attics can offer many opportunities• You may be able put a small beam in a large

attic• You don’t have to worry about the effects of

weather• Attics may contain HVAC ducts and wiring that

can affect the performance of your antenna• RFI is a consideration• Be careful not to step through the sheet rock!


In The YardIn The Yard

• Verticals can be hidden in trees– You will have to deal with the radial/ground problems– Vertical dipoles may be possible in higher trees– Flag pole and bird feeder antennas may be possible

• Thin wire between trees or from a tree to the house may work– Thin wire is easy to break and you may have to

replace it often• You may be able to string wire along the top of a

fence– An antenna this low will probably be good for NVIS

not DX though


On the HouseOn the House

• Rain gutters have been used by some– You will have to bond all of the sections

together– Corroded connections can generate

harmonics and RFI problems– This system will probably be unbalanced

• You could run a wire around the house under the eves– May not be very effective on a stucco house


TV AntennasTV Antennas

• A TV antenna could be used as a vertical– The TV lead-in (300 ohm line) could be part of the

antenna– The actual TV antenna is a capacity hat

• FCC regulations state that HOAs must allow TV antennas

• You could use a log periodic for VHF/UHF– 6M, 2M, 220, 440 and 1.2 GHz– It looks like a TV antenna and will receive TV signals


On The RoofOn The Roof

• A wire antenna is very hard to see from the ground if it is low to the roof– This is the highest location on the house– This location has the least RF obstructions

• Two story houses are even better– The antenna is higher and harder to see from the

ground• You can build a very good dipole or multiband

doublet on the roof– By bending the ends you should be able to cover 40

through 6 M– Use chimneys, vent pipes and other existing items on

your roof for supports


How Well Do They Work?How Well Do They Work?

Results & LimitationsResults & Limitations


What Worked and NotWhat Worked and Not

• 20 M Ham Stick Dipole in the attic – My first try– I couldn’t hear much (weak signals and lots of RFI)

• 20 M Wire Dipole on the roof– Worked great (good SWR and DX)– Single band though

• Parallel Dipoles on the roof– Only would load up on lowest band– Tried a couple with no good results– More wire on the roof for people to see


Back to BasicsBack to Basics

• Next I went back to the 20 M Dipole and added an auto tuner– Worked on 20 – 10M– More than one band finally– But what about 40M?

• Tried a 40M Dipole with bent ends and the tuner– Worked good on 40 and 15M– Not so good on 20M but it would load


My Bent AntennaMy Bent Antenna• Finally tried a G5RV Jr.

– Half size G5RV (51 ft.)– 16 ft. 450 ohm ladder line– Balun to 50 ft of 9913 coax– Auto tuner

• The last 6 to 8 ft of each end is bent at about a right angle to the main portion of the antenna

• This antenna works on 40 through 6 meters and fits in less than 40 linear feet– 15M is the worst band but it does work

• I have been using this antenna for over 3 years


Antenna View from Front of HouseAntenna View from Front of House

VHF/UHF/1.2 GHz Whip

End of G5RV Jr.

Bend Point


Back End of G5RV Jr.Back End of G5RV Jr.

Antenna Wire

Tie Cord


G5RV Jr. Antenna ScanG5RV Jr. Antenna Scan


DX ResultsDX Results

• Worked – 2004 to Present (a few were with other wire or mobile antennas)– 162 Entities– 370 Band/Entities– 36 CQ Zones

• Best DX with G5RV Jr.– Scarborough Reef - BS7H (20M CW)– Andaman Is. - VU4AN/VU3SIG (20M SSB)– Chalogos - VQ9JC (20M CW)– Peter I - 3Y0X (40M SSB)– St. Brandon - 3B7C (20M CW)


Relative PerformanceRelative Performance

• You will be a Little Pistol Station– You will not hear all of the stations that the Big Guns

hear– You will hear a lot of RFI– If you wait for the best propagation, you have a

chance– CW and PSK-31 will help– When conditions are good, you will hear a lot of DX– Sunspots help…


RFIRFI

The WAE AwardThe WAE AwardHow to “Work All Electronics” in your How to “Work All Electronics” in your

househouse


Receiving RFIReceiving RFI

• You will hear most of the electronics in your house– TV sets– Computer networks, routers, etc.– Switching type wall warts– Battery chargers

• Ferrites may help on some devices• In a pinch you may need to turn things off to

work that “rare one”– Identify the culprits ahead of time


Transmitted RFITransmitted RFI• Worst RFI receivers

– Phones, cordless and regular, answering machines • 5 GHz cordless phones seem to be better

– Home Theater amplifiers, stereos, etc• Rear channel speaker leads are great antennas

– X10 Power Line controllers– Paper shredders– Burglar alarms– Sprinkler controllers

• Check Jim Brown, K9YC’s material on ferrites and applications– Filters and ferrites may help

• QRP (PSK-31 and CW) may be solutions


QRO?QRO?

Haven’t had enough RFI?Haven’t had enough RFI?

Not for the faint at heart!Not for the faint at heart!


If You Must QRO – Be PreparedIf You Must QRO – Be Prepared

• Solve your 100W problems first• You may actually destroy some electronics• My DOA list @ 1300 W

– One answering machine ($50)– One Ethernet interface for LaserJet Printer ($300)– Max power is now 600 W

• Burglar Alarm– Bell would ring at power levels over 300W– Solved by a .01uF capacitor

• Seriously consider RF exposure levels!– Limit duty cycle


Reference MaterialReference Material

Good reading and useful antenna Good reading and useful antenna informationinformation


Some Good Books on Some Good Books on Stealth/Clandestine AntennasStealth/Clandestine Antennas

• Stealth Amateur Radio– By Kirk Kleinschmidt, NT0Z– ARRL Publications

• Low Profile Amateur Radio– By Al Brogdon, W1AB– ARRL Publications

• ARRL Antenna Book– Edited by Dean Straw, N6BV


Good Luck & Good DXGood Luck & Good DX

de AE6RRde AE6RR

clandestine antennas for amateur radio

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