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NCDXC June 08 Page 1 of 46 AE6RR – Clandestine Antennas Clandestine Antennas for Amateur Radio By Craig Bradley, AE6RR - --- -- - --- - “BY PROHIAS”

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Presentation on theme: "NCDXC June 08 Page 1 of 46 AE6RR – Clandestine Antennas Clandestine Antennas for Amateur Radio By Craig Bradley, AE6RR - --- -- - --- - “BY PROHIAS”"— Presentation transcript:

1 NCDXC June 08 Page 1 of 46 AE6RR – Clandestine Antennas Clandestine Antennas for Amateur Radio By Craig Bradley, AE6RR “BY PROHIAS”

2 NCDXC June 08AE6RR – Clandestine AntennasPage 2 of 46 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

3 NCDXC June 08AE6RR – Clandestine AntennasPage 3 of 46 This Presentation Clandestine vs. Stealth antennas What makes an antenna work Multiband antennas Possible locations How well do they work? RFI QRO Reference Material

4 NCDXC June 08 Page 4 of 46 AE6RR – Clandestine Antennas Clandestine vs. Stealth Antennas What is the difference?

5 NCDXC June 08AE6RR – Clandestine AntennasPage 5 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

6 NCDXC June 08AE6RR – Clandestine AntennasPage 6 of 46 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

7 NCDXC June 08 Page 7 of 46 AE6RR – Clandestine Antennas What Makes Antennas Work? Get the RF in the Air

8 NCDXC June 08AE6RR – Clandestine AntennasPage 8 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”

9 NCDXC June 08AE6RR – Clandestine AntennasPage 9 of 46 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

10 NCDXC June 08AE6RR – Clandestine AntennasPage 10 of 46 Bent Antenna Example Conventional wisdom says that you can’t bend an antenna back on it's self SteppIR does not agree…

11 NCDXC June 08AE6RR – Clandestine AntennasPage 11 of 46 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 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

12 NCDXC June 08AE6RR – Clandestine AntennasPage 12 of 46 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 …

13 NCDXC June 08AE6RR – Clandestine AntennasPage 13 of 46 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)

14 NCDXC June 08AE6RR – Clandestine AntennasPage 14 of 46 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”

15 NCDXC June 08AE6RR – Clandestine AntennasPage 15 of 46 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 lineSWR at Load SWR at Input Total Line Loss RG-8X dB Beldon dB 450-Ohm dB 450-Ohm w/ 20 Ohm load dB

16 NCDXC June 08AE6RR – Clandestine AntennasPage 16 of 46 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…

17 NCDXC June 08AE6RR – Clandestine AntennasPage 17 of 46 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

18 NCDXC June 08AE6RR – Clandestine AntennasPage 18 of 46 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

19 NCDXC June 08AE6RR – Clandestine AntennasPage 19 of 46 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

20 NCDXC June 08 Page 20 of 46 AE6RR – Clandestine Antennas Multiband Antennas Want to get on more than one band?

21 NCDXC June 08AE6RR – Clandestine AntennasPage 21 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

22 NCDXC June 08AE6RR – Clandestine AntennasPage 22 of 46 Types of Multiband Antennas Trapped Verticals –We already talked about verticals Horizontal Balanced Wire Antennas –Fan or parallel dipoles –Trapped dipoles –Doublets –G5RVs

23 NCDXC June 08 Page 23 of 46 AE6RR – Clandestine Antennas Possible Locations Time to use your imagination

24 NCDXC June 08AE6RR – Clandestine AntennasPage 24 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

25 NCDXC June 08AE6RR – Clandestine AntennasPage 25 of 46 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!

26 NCDXC June 08AE6RR – Clandestine AntennasPage 26 of 46 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

27 NCDXC June 08AE6RR – Clandestine AntennasPage 27 of 46 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

28 NCDXC June 08AE6RR – Clandestine AntennasPage 28 of 46 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

29 NCDXC June 08AE6RR – Clandestine AntennasPage 29 of 46 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

30 NCDXC June 08 Page 30 of 46 AE6RR – Clandestine Antennas How Well Do They Work? Results & Limitations

31 NCDXC June 08AE6RR – Clandestine AntennasPage 31 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

32 NCDXC June 08AE6RR – Clandestine AntennasPage 32 of 46 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

33 NCDXC June 08AE6RR – Clandestine AntennasPage 33 of 46 My 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

34 NCDXC June 08AE6RR – Clandestine AntennasPage 34 of 46 Antenna View from Front of House VHF/UHF/1.2 GHz Whip End of G5RV Jr. Bend Point

35 NCDXC June 08AE6RR – Clandestine AntennasPage 35 of 46 Back End of G5RV Jr. Antenna Wire Tie Cord

36 NCDXC June 08AE6RR – Clandestine AntennasPage 36 of 46 G5RV Jr. Antenna Scan

37 NCDXC June 08AE6RR – Clandestine AntennasPage 37 of 46 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)

38 NCDXC June 08AE6RR – Clandestine AntennasPage 38 of 46 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…

39 NCDXC June 08 Page 39 of 46 AE6RR – Clandestine Antennas RFI The WAE Award How to “Work All Electronics” in your house

40 NCDXC June 08AE6RR – Clandestine AntennasPage 40 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

41 NCDXC June 08AE6RR – Clandestine AntennasPage 41 of 46 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

42 NCDXC June 08 Page 42 of 46 AE6RR – Clandestine Antennas QRO? Haven’t had enough RFI? Not for the faint at heart!

43 NCDXC June 08AE6RR – Clandestine AntennasPage 43 of 46 If You Must QRO – Be Prepared Solve your 100W problems first You may actually destroy some electronics My DOA 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

44 NCDXC June 08 Page 44 of 46 AE6RR – Clandestine Antennas Reference Material Good reading and useful antenna information

45 NCDXC June 08AE6RR – Clandestine AntennasPage 45 of 46 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

46 NCDXC June 08 Page 46 of 46 AE6RR – Clandestine Antennas Good Luck & Good DX de AE6RR


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