Generation 5 - 22-element 160m-6m Directional Stealth Attic Array

The 4th generation of attic antennas here at the AC0C QTH worked great compared to prior configurations - however, there were so many refinements and improvements made in the recent rebuild series, that I've decided to call this the 5th generation. Take a look a the details in the tabs to the left - and I hope you will agree. This may be the most elaborate attic antenna on earth!

An introduction and overview of the system's capabilities are given below.  With more complete details, including design methodology, build details and measurements, are found in the REBUILD tabs to the left.

More updates to this system in the SO2R project coverage HERE

 What's New in Generation 5

Fundamental changes from the Generation 4 array include:

• Full integration of So2r operation - and antennas redesigned with So2r adjacent band operation examined
  
  
• Novel use of stubs to augment the prior relay-based decoupling
  
  
• New fixed-orientation antennas for 10m to take advantage of the improving SFI
  
  
• Complete instrumentation of all elements to facilitate fine tuning - planned in Gen 4 but never fully implemented

Almost every aspect of the system has been reworked and improved.  

 Design Considerations

This antenna is really a logical extension of the prior work.   Major design objectives include:

• All band coverage - Provide 160-6m coverage with directional capability where practicle.  
    
• Use mono-band designs where possible - this simplifies the optimization for that band and allows simplified matching (hairpins, etc) which are band specific and avoid traps or other multi-band compromises 
  
  
• Manage parasitics  - Because so many of the ham bands are harmonically related, provide some method to detune the unused elements so that they don't disrupt the antenna's pattern
  
  
• Measure  - W8WWV's RVM system is used to actually measure each element's actual current and phase relationship.  Antennas are initially built to rough dimensions and then trimmed to the model's indicated phase target.  Once trimmed, the actual phase and currents as measured by RVM are used in the model as element sources.  The model then provides a prediction of the overall radiation pattern based on actual current/phase values. 
  
  
• Automate - The array functions are automated to the extent the antenna will follow rig band selection and emulate a rotor for direction control integration with software.

 Generation 5 Array Antennas

• Multi-function dipole for 160, 80 and 12m. Apex at 45 feet (11m).   Loaded dipole on 160m, trapped as a full size 80m dipole. Also serves as the DE for the 12m beam.  On 12m and 160m, hairpin matches are automatically activated to offset the lower resistance feed point (due to the loading coils on 160m, and the beam on 12m).
  
  
• 40m – phase-driven full size 2-element electrically reversible v-beam yagi        
  
  
• 30m – full sized 2-element v-yagi - fixed east
  
  
• 20m – full sized 2-element electrically reversible v-yagi (3 elements total)
  
  
• 17m - dipole sharing the 15m DE feed point
  
  
• 15m - full sized 2-element electrically reversible yagi (3 elements total)
  
  
• 12m - full sized 2-element electrically reversible yagi (3 elements total). The DE shares the same element as the 80/160m dipole and is trapped for 12m.
  
  
•  6M – 3-element bi-directional figure-8 pattern pointing ENE-WSW
  
  

Size:  Attic volume is 16' high, 20' in "beam length" and 40' wide.  The apex of the house is about 45' (11.3 m) above ground level.  The rear of the house slopes down and away giving an improved "east beaming" height above ground level. 

 Work Remaining

• Conversion of the 30m parasitic to a phased drive reversible
  
  
• Replace current  2nd rig manual directional controls with rotor emulation
  
  
• Add directors to the 17m dipole DE to create beam functionality
  
  
• Add 20m and 17m functionality to the 15m N/S dipole

Construction Highlights

80M Trap - 160M Loading Coil    

Traps are used on the driven element in 2 places.  Near the apex for 12m and then again for 80m.  With the traps, the antenna is resonant at 24.900, 3.740 and 1.825 MHz.

Given the troubles with the prior generation traps, I wanted to ensure that the new traps were indestructible. The new design is 1/4" copper tubing on a 5" form.  The capacitor is a 15KV 100 pF 5% Russian surplus unit.  Hi-Pot testing of the caps showed only a few uA of leakage at 15KV.  I did not measure the traps Q but would guess its in the 300+ range based on similar work.

The only compromises that were made were putting the metal components within the coil and the use of dissimilar metals in direct contact.  As the coils would be not used in the outdoor weather environment,I felt these were negligible factors on the overall design.

After having participated in many RTTY contests, I can say the traps are performing very well indeed!

Antenna Mounted Isolation Modules

Detuning of the elements not used for a given antenna is accomplished by the isolation modules. 

The module allows the center of the dipole elements to be open or shorted - and may incorporate stubs to accommodate different behavior on different frequencies.  Ten stubs and over 50 relays are required to imp element the array's functions. 

Construction of the module varies from simple to complicated.  The dipole control module is shown here and represents the extreme case.

Below you can see a simpler control module, this one for the 15m director.  And with a stub hanging below.  For more explanation of the function of the stub and interaction with the control module, see the page on the 15m rebuild here.

Attic Mounted Relay Switching Module

The isolation module relays are driven from a master control board in the attic. Inputs to the module are:

1. BCD data from the shack's Ameritron automatic antenna switch
2. Selection of the driven elements from the shack's control head
3. Selection of the open/short combination to provide minimum interference with the antenna pattern
4. Buffers the direction line (east/west)

The switching module decodes these inputs and switches the relays to the correct positions.

The power supply is fused on both the primary and secondary side.  RF bypassed on both sides.

All lines into and out of the module are bypassed by 200 mH inductors and 0.1 uF caps in an L network.  No RFI effects have been observed to date.

The terminal strips allow easy connection of the various lines running to the relay and power lines.  A DB15 connects the lines from the control heads.   IC content of the board is minimal - a BCD decoder and relay driver arrays.

The heat sinks as shown here are inadequate and need to be replaced or supplemented.

The LEDs adjacent to each connection help in diagnostics and confirm which lines are active .

To facilitate diagnostics,a jack on the board connects to a remote push-button switch to allow local override and switching of the antenna direction and 15/17m lines.  A DIP switch allows selection of open/short combinations.

The switching module is mounted on a backing board which is secured to the studs in the attic.  The backing board provides a DC power supply for the module.  And serves as a mounting plate for the Ameritron 8-position antenna switch head.

So2r Integration

So2r operation is supported with bands 40m, 20m and 15m enabled on both rigs.  All other bands are supported on a single rig.  A separate attic-based controller (below) works with the relay switching and shack control head to provide fully automatic antenna selection and switching.  

Selection of antennas is made via a KK1L 2x6 antenna switch, shown here at left.

A set of 5B4AGN W3NQN-style BPF auto-switching modules in the shack provide rig isolation.

Shack Mounted Control Module

NOTE:  Shown below is the controller as implemented with the initial single-radio model. It's replacement will incorporate this circuitry with an added 2nd rig capability to facilitate automatic direction control.

The heart of the system is the control module.  It's tied into the rest of the shack hardware as summarized by the topology in the drawing below.

The control head is shown below.  Functions are labeled.  Notice that auto-tuner control as well as pulse/carrier buttons are present to make amp tune-up easy.

 Attic Views

A few interesting photos of the antenna is shown here. It's a bit hard to photograph what is mostly a wire-based attic antenna system. But these pictures should give you a preview.

More complete details - and more photos - are contained in the rebuild sections.  

Parts for the "Two and a Half" 10m beams

40m phased array control module and coax stubs

160m/80m/12m dipole control module and stubs

15m directory control module