Clandestine Antennas for Amateur Radio By Craig Bradley, AE 6 RR “BY PROHIAS” - • • • -- • • --- • • • - • • • 1
Background • First licensed as WV 6 SVW & WA 6 SVW – 1961 to 1967 – No antenna restrictions (except parents) – Life was good • Relicensed in 2004 as AE 6 RR – 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 NCDXC June 08 AE 6 RR – Clandestine Antennas 2
This Presentation • • Clandestine vs. Stealth antennas What makes an antenna work Multiband antennas Possible locations How well do they work? RFI QRO Reference Material NCDXC June 08 AE 6 RR – Clandestine Antennas 3
Clandestine vs. Stealth Antennas What is the difference? NCDXC June 08 AE 6 RR – Clandestine Antennas Page 4 of 46
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 5
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 6
What Makes Antennas Work? Get the RF in the Air NCDXC June 08 AE 6 RR – Clandestine Antennas Page 7 of 46
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” NCDXC June 08 AE 6 RR – Clandestine Antennas 8
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 9
Bent Antenna Example • Conventional wisdom says that you can’t bend an antenna back on it's self • Stepp. IR does not agree… NCDXC June 08 AE 6 RR – Clandestine Antennas 10
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 11
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 … NCDXC June 08 AE 6 RR – Clandestine Antennas 12
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) NCDXC June 08 AE 6 RR – Clandestine Antennas 13
A Word on Transmission Lines • Transmission lines have losses – Usually rated as d. B 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” NCDXC June 08 AE 6 RR – Clandestine Antennas 14
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 N 6 BV) Type of line SWR at Load 19. 91 SWR at Input 5. 24 Total Line Loss 6. 0 d. B Beldon 9913 20. 33 10. 01 3. 043 d. B 450 -Ohm 2. 47 2. 41 0. 137 d. B 450 -Ohm w/ 20 Ohm load 20. 25 16. 46 0. 934 d. B RG-8 X NCDXC June 08 AE 6 RR – Clandestine Antennas 15
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… NCDXC June 08 AE 6 RR – Clandestine Antennas 16
Balanced Antennas • • • Dipoles, Doublets, G 5 RVs, 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 NCDXC June 08 AE 6 RR – Clandestine Antennas 17
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 80 M, you may need to consider a loaded antenna if space is limited – RFI noise may be a big problem here NCDXC June 08 AE 6 RR – Clandestine Antennas 18
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 19
Multiband Antennas Want to get on more than one band? NCDXC June 08 AE 6 RR – Clandestine Antennas Page 20 of 46
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 21
Types of Multiband Antennas • Trapped Verticals – We already talked about verticals • Horizontal Balanced Wire Antennas – Fan or parallel dipoles – Trapped dipoles – Doublets – G 5 RVs NCDXC June 08 AE 6 RR – Clandestine Antennas 22
Possible Locations Time to use your imagination NCDXC June 08 AE 6 RR – Clandestine Antennas Page 23 of 46
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 24
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! NCDXC June 08 AE 6 RR – Clandestine Antennas 25
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 26
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 27
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 – 6 M, 220, 440 and 1. 2 GHz – It looks like a TV antenna and will receive TV signals NCDXC June 08 AE 6 RR – Clandestine Antennas 28
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 29
How Well Do They Work? Results & Limitations NCDXC June 08 AE 6 RR – Clandestine Antennas Page 30 of 46
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 31
Back to Basics • Next I went back to the 20 M Dipole and added an auto tuner – Worked on 20 – 10 M – More than one band finally – But what about 40 M? • Tried a 40 M Dipole with bent ends and the tuner – Worked good on 40 and 15 M – Not so good on 20 M but it would load NCDXC June 08 AE 6 RR – Clandestine Antennas 32
My Bent Antenna • Finally tried a G 5 RV Jr. – – Half size G 5 RV (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 – 15 M is the worst band but it does work • I have been using this antenna for over 3 years NCDXC June 08 AE 6 RR – Clandestine Antennas 33
Antenna View from Front of House End of G 5 RV Jr. VHF/UHF/1. 2 GHz Whip Bend Point NCDXC June 08 AE 6 RR – Clandestine Antennas 34
Back End of G 5 RV Jr. Antenna Wire Tie Cord NCDXC June 08 AE 6 RR – Clandestine Antennas 35
G 5 RV Jr. Antenna Scan NCDXC June 08 AE 6 RR – Clandestine Antennas 36
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 G 5 RV Jr. – – – Scarborough Reef - BS 7 H (20 M CW) Andaman Is. - VU 4 AN/VU 3 SIG (20 M SSB) Chalogos - VQ 9 JC (20 M CW) Peter I - 3 Y 0 X (40 M SSB) St. Brandon - 3 B 7 C (20 M CW) NCDXC June 08 AE 6 RR – Clandestine Antennas 37
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… NCDXC June 08 AE 6 RR – Clandestine Antennas 38
RFI The WAE Award How to “Work All Electronics” in your house NCDXC June 08 AE 6 RR – Clandestine Antennas Page 39 of 46
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 NCDXC June 08 AE 6 RR – Clandestine Antennas 40
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 – – X 10 Power Line controllers Paper shredders Burglar alarms Sprinkler controllers • Check Jim Brown, K 9 YC’s material on ferrites and applications – Filters and ferrites may help • QRP (PSK-31 and CW) may be solutions NCDXC June 08 AE 6 RR – Clandestine Antennas 41
QRO? Haven’t had enough RFI? Not for the faint at heart! NCDXC June 08 AE 6 RR – Clandestine Antennas Page 42 of 46
If You Must QRO – Be Prepared • Solve your 100 W problems first • You may actually destroy some electronics • My DOA list @ 1300 W – One answering machine ($50) – One Ethernet interface for Laser. Jet Printer ($300) – Max power is now 600 W • Burglar Alarm – Bell would ring at power levels over 300 W – Solved by a. 01 u. F capacitor • Seriously consider RF exposure levels! – Limit duty cycle NCDXC June 08 AE 6 RR – Clandestine Antennas 43
Reference Material Good reading and useful antenna information NCDXC June 08 AE 6 RR – Clandestine Antennas Page 44 of 46
Some Good Books on Stealth/Clandestine Antennas • Stealth Amateur Radio – By Kirk Kleinschmidt, NT 0 Z – ARRL Publications • Low Profile Amateur Radio – By Al Brogdon, W 1 AB – ARRL Publications • ARRL Antenna Book – Edited by Dean Straw, N 6 BV NCDXC June 08 AE 6 RR – Clandestine Antennas 45
Good Luck & Good DX de AE 6 RR NCDXC June 08 AE 6 RR – Clandestine Antennas Page 46 of 46
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