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Clandestine Antennas
for Amateur Radio
By
Craig Bradley, AE6RR
“BY PROHIAS”
-••• -•-NCDXC June 08
AE6RR – Clandestine Antennas
•--• •-• --- •••• •• •- •••
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Background
• 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
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This Presentation
•
•
•
•
•
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Clandestine vs. Stealth antennas
What makes an antenna work
Multiband antennas
Possible locations
How well do they work?
RFI
QRO
Reference Material
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Clandestine vs. Stealth
Antennas
What is the difference?
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Stealth 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
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Clandestine 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
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What Makes Antennas
Work?
Get the RF in the Air
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Some 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”
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Bent 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
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Bent Antenna Example
• Conventional
wisdom says
that you can’t
bend an
antenna back
on it's self
• SteppIR does
not agree…
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Antenna 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 missmatch (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
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A 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 …
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Reflected 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)
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A 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”
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Transmission Line Loss
The 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
19.91
SWR at
Input
5.24
Total Line
Loss
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
RG-8X
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Unbalanced 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…
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Balanced 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
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Loaded 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
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Loop 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
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Multiband Antennas
Want to get on more than one
band?
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Required 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
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Types of Multiband Antennas
• Trapped Verticals
– We already talked about verticals
• Horizontal Balanced Wire Antennas
– Fan or parallel dipoles
– Trapped dipoles
– Doublets
– G5RVs
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Possible Locations
Time to use your imagination
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Indoors
• 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
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Attic
• 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!
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In 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
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On 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
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TV 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
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On 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
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How Well Do They Work?
Results & Limitations
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What 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
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Back 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
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My Bent Antenna
• Finally tried a G5RV Jr.
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–
–
–
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
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Antenna View from Front of House
End of G5RV Jr.
VHF/UHF/1.2 GHz Whip
Bend Point
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Back End of G5RV Jr.
Antenna Wire
Tie Cord
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G5RV Jr. Antenna Scan
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DX 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)
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Relative 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…
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RFI
The WAE Award
How to “Work All Electronics” in your
house
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Receiving 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
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Transmitted 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
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QRO?
Haven’t had enough RFI?
Not for the faint at heart!
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If 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
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Reference Material
Good reading and useful antenna
information
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Some Good Books on
Stealth/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
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Good Luck & Good DX
de AE6RR
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