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Web site home page: www.ac0c.com Popular website destinations at www.ac0c.com:
Please stop by! Thank you for visiting ac0c. 73/jeff
-----QSL INFO HERE----- QSL: 100% upload to LoTW and eQSL.cc automatically. Look for confirmation within a week or so of the QSO. DX QSL Direct OK - please include SAE *AND* $1 - or 1-IRC. For USA QSO, I will reply 100%. SASE appreciated! I print my own custom paper QSL and these are done on a batch basis about once each year- so if you don't' get a reply right away to your SASE, don't worry - it will come eventually. If you need it faster, send me an email and I will fix you up!
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The Shack.
Shack is setup with an So2r configuration as follows:
40/20/15m run station: Yaesu FT-2000 with NS roofing filter, 3 KHz 2nd RX, PEP and other mods Full custom SB-200 with dual Gi7Bs 160-6m roaming station: Yaesu FT-DX5000MP - no mods, DMU-2000, SM-5000 Alpha 76PA
Antennas - all fixed position, attic mounted with 11.3m (45') apex - allowing full 160-10m all band operation: A. 3-element trapped inverted-v wire. Serves as DE for the 12m 2-element reversible beam. Extensions for 80m and trapped for 160m. B. 3-element Mosley Pro 57 modified for reversible operation covering 15/17 - at 30' (9m). C. 2-element v-wire beam for 30m fixed east. D. 2-element v-wire phase-driven beam for 40m, reversible. E. Dual 2-element v-wire beam for 20m, reversible. F. 10m is served from a trio of fixed antennas: Separate 2-element fixed beams for east and another for west. And an E/W dipole for SA/JA. G. 3-element bidirectional fixed for 6m Shack mounted MFJ-998 automatic ATU and a Ameritron RAC-12 remote antenna switch with custom control head for automatic antenna selection and with capability for automatic direction selection via software or button - for easy remote operation. So2r features via custom board and KK1L 2x6 switch. The Skimmer SDR Array: Homebrew 10-band Softrock-based skimmer array covering all bands 160-6. Centralized telnet spot feed. Clifton Labs Z10000 behind a Minicircuits-based preamp. Requires 2 high-speed computers to host the Delta 1010LT sound cards and the Skimmer sessions. Allows simultaneous monitoring of all CW activity on all HF bands based on the skimmer decodes from the local antennas. More details below. Other shack hardware: KK7UQ PSK IMD meter, Telepost LP-100a vector power meter with dual feeds. Daiwa CN-801. Microham Microkeyer II and Microkeyer digital interfaces. Begalli paddle. Infrasonic Quartet internal sound card with a pair of N8LP's excellent LP-PAN driving WU2X's customized version of PowerSDR Pretty Betty. Softrock v9.0 multi-band RX for transmitted signal monitoring (spectrum analyzer mode) and for use on occasion as a spotting rig. Heavily abused Heathkit dummy load. Primary Shack Computer: Integrated HRD + DXLABS suite running on a homebrew 3.5Ghz Intel OC Quad 6600 with 4GB RAM and 4x500 gb drives in RAID 1+0 configuration. Graphics Nvidia 260 + 9500GT driving 3 x 28" external LCD. 12" LCD for the DMU. This PC also hosts 4 of the 11 skimmer sessions from the Skimmer SDR Array. Secondary Shack Computer: 7 of 11 CW Skimmer sessions are hosted on a second PC - 3.9G Intel Dual Core with 2GB RAM and 4x500 gb drives in RAID 1+0. And when traveling, remote access and other goodies performed using the HP/Compaq 2.4G 17" LCD workstation notebook - a real workhorse. -------------------------------------------------------------------------------------------------------------------- About AC0CI prefer CW and RTTY. Interest areas are amps, antennas/modeling and lately, renewing my C-code writing capability which is being used to program some Atmel AVR MCU - the last one I programmed was in 1987 - and things have come a LONG way since then. Received the mixed mode DXCC in Sept 2009 after being stuck at 99 confirmed for a long time. As of 1/1/2010 - 129 confirmed/149 worked. Improving my CW fist after about 27 years QRT. Thanks to everyone I've worked and had the patience to put up with my many CW sending errors. Ham History: 1974 - Novice - call WN0QPC, 1975 - General - call WB0QPC 1976 - Advanced - call WB0QPC, and 1976 - Extra - AC0C Elmers: WS4Y Bill Turney introduced a wide-eyed 10 year old kid to ham radio. WB0SSB Larry Smith for keeping me out of trouble and into radio in my early years. My XYL who pushed me back into the hobby by ignoring all my "no outside antennas are allowed here" excuses. K0RU for getting me hooked on antenna modeling, and generally supplying my antenna hardware sourcing needs - in addition to being one of the most selfless individuals I have had the privilidge to know. W5VIN Charlie who taught me what an amp is and how they work - very much in the tradition of Bill Orr - and to this day remains a great friend and mentor - and a guy who helps me keep it all in perspective. And to Bill Carver and Jack Smith - two of the most knowledgable and practical engineers I have had the pleasure of learning from. ===================================================================== Layout of Station Software and Platforms.There are 3 28" 1920x1200 LCD HDTV monitors dedicated to the shack operation. The screen configuration moves around depending on situation. But typically the center monitor hosts the excellent HRD DM780 for PSK, RTTY and CW. Shown to the right is CW Skimmer. I use DM780 for all the QSO log inputs and digital modes work. DM780 is pretty mouse-centric, however, with some custom macros, it's also capable of being a very competent contest interface.
The left monitor (below) accomidates logging related programs from the most excellent DX Labs Suite - especially the DXKEEPER program which provides automated LoTW and eQSL upload/download/sync functions! This combination of programs provides logging, QRZ lookup, collects needed spots and gives a map showing the contact location.
On the right monitor - Hosts the PowerSDR interface to the station's Softrock SDR. PowerSDR and Skimmer are linked so clicking on either screen QSYs the Softrock and decodes the CW. A 196 khz segment of any band can be monitored with an Infrasonic Quartet sound card in the station computer. The combination of the FT2000 excellent ergonomics and tradtiional rig design, combined with the LPPAN/SDR/PowerSDR interface offers the best of both the traditional and SDR interface operating in concert.
A consolidated telnet feed to the Spot Collector application comes via K1TTT's Wintelnetx program. Wintelnetx gathers the individual data streams from the 10 band CW Skimmer array and the Skimmer session tied to the LPPAN. Skimmer feeds are tracked in each window of the Wintelnetx for easy functional monitoring. And the total stream runs into the spotting program where it's filtered for the needed spots.
======================================================================= Homebrew Projects. See the AC0C Homebrew and Antennas page for full details and the latest updates on all the projects below - and more. Click here!
Many of the home brew projects are summarized below. And there are 2 more that are worth mentioning. 1. Replacement roofing andd selectivity filters for the FT2000. This otherwise FB rig has a sub-par IMDDR3 performance characteristic due largely to the implementation choices in the 1st IF. Charlie W5VIN, Daniel YO3GJC and I are working with one of the worlds' premier filter builders to develop an alternative filter solution for the FT2000. The initial designs now in construction include a true 2.4KHz 69.45Mhz filter with a 2.8:1 shape factor targeted to replace the existing "3KHz" roof (which measures close to 7KHz in reality). In addition, we have cominga 350hz cw/data mode 2nd IF filter featuring a true-zero-ring design topology - and a 1.8KHz SSB contest mode selectivity filter. If you are interest in this project, you can follow the developments as they are published on the Yahoo "FT2000_new" user group. Based on the filter model, the overlay of the actual FT2000 3 KHz stock roofing filter. Notice the huge difference in skirt width. The irregular shape of the stock filter response is likly related to filter termination.
2. In support of the FT2000 filter evaluation, Charlie W5VIN and I are working with Paul N2PK to modify the excellent N2PK VNA for functionality above 70Mhz. Results so far provide a 75Mhz upper frequency limit with >90 db of functional dynamic range. If we are lucky, we will be able to push this up to about 110db although in it's current rough implementation, the functionality is sufficient for the needs of the FT2K filter project. =================================================================== Home Brew Bench Equipment I'm building a series of bench modules to provide basic functions. The practical need is there - and I've been wanting to build these for quite a long time. Fixed Voltage Module - this is essentially a header connection strip and is powered by a salvaged computer switching-style power supply. High current capability in +12, +5, +3.3, and moderate current capability in +9, -5 and -12v are availabe on the front panel. Internal termination resistors provide a minimum current to ensure the power supply voltage regulation remains in check. And each output is seperately switched in addition to a master switch.
Dual Variable Power Supply - the module contains linear regulators with output of 30V @ 2A. Voltage and current for each output is monitored by the autoranging DVM shown to the right - Current is indirectly read as a voltage so no switching between V/I at the DVM is required - switching on the module selects the output and V/I mode for monitoring. Short circuit, over current and thermal shutdown are integrated into the regulator IC. The only difficult part of the variable voltage design was the selection of the resistors. Log taper of the correct size were not ready available so I used dual-gang pots and paralleled the values to get the right resistance. The voltage is very smoothly adjustable as a result. Picture below (right). Waveform Generator Module - Based on the Exar XR2206 chip, the output is quite low in distortion products and the circuit is simple to implement compared to a microcontroller or DDS solution. Sine, square and triangle modes - as well as variable duty cycles are supported. Output levels are adjustable from 0-5V P-P. Picture below (left).
DVM - next and probably the final module is a DVM that will provide frequency and level indication for the waveform generator, and will monitor the V/I of all the various power supply sources. In addition to these monitor functions, front panel connections for voltage, current, frequency and temperature measurement. This module is based around a dedicated microcontroller and that will make it easy to add more functionality, optimize accuracy, etc in the future. =================================================================== SoftRock Lite v9.0 BPF 90% of the RX performance of the Flex 5K, at 5% the price!!! Created by Tony Parks KB9YIG as an easy way to try SDR. It's turned into a very robust and high performing SDR. Below are pictures of the Softrock Lite v9.0 with band-pass filter add-on board, and a Clifton Labs buffer amp. Modifications from the "standard" configuration allow the rig to run completely from the USB port power line. This configuration provides coverage of all bands 160m-10m. With the buffer amp, rig sensitivity is very good: S9 = -73 dbm @ 50 uV S1 = -110 dbm @ 1 uV Noise floor = -123 dbm Measurements based on performance of a HP Compaq 8710w notebook. The notebook's built-in sound card is exceptionally quiet for a notebook computer although the sample frequency is limited to 48KHz. There is an available input on the main station PC to support this rig and it would serve as a nice spotting platform but that's a project for anotherday. All signal demodulation and filtering is done in the PowerSDR software package. PowerSDR is the standard applicaiton for the Flex 5K line and is open-sourced. All functional performance of the rig including brick-wall digital filtering is provided by PowerSDR.
For anyone wanting to try out SDR technology, the Softrock is a fantastic way to get started. Purchase Softrock kits: http://www.kb9yig.com/ Softrock "Heathkit-style" Build Notes: http://wb5rvz.com/sdr/
=================================================================== 10 Band CW Skimmer Array After looking (and lusting) over the very excellnet multiple-band skimmer arrays at K3LR and K4TD, I wanted to see if the similar performance could be created at a lower price point. This is the results of that work. The skimmer inputs are based on the Softrock II - a $15 USD crystal controlled single-band SDR. There is one SDR for all ham bands 160-6, inclusive of WARC. From the antenna input follows a homebrewMini Circuits MMC preamp at the head - 31 db gain with a NF of about 2. The Softrock LO suppression measured at the antenna input is only about -45db down soan excellent Jack Smith Z10000 bufferprovides70-100db of LO isolation. The buffer feeds into an 8-way Mini Circuitssplitter, and the 3 lowest bands share one tap via a homebrew splitter. MDS is better than -120dbm on all bands.
Some of the modules require a low noise oscillator module as crystals of the proper frequency were not availble. These modules can be seen under the SMT bypass cap, below the left black transistor. The Abercrom single-chip low-noise oscillator module is 2x3 mm in size.
The individual SDR feed into Delta1010LT cards and requires 2 computers to process the 10 instances of CW Skimmer. The output of the CW Skimmers is a telnet feed. And the K1TTT Wintelnetx program consolidates all of these feeds into a single stream. The resulting combined telent stream is dupe-checked and the sorted for NEEDED spots by the DX Lab Suite Spot Collector program. Resources: Softrock Lite by Tony Parks: https://www.kb9yig.com/ Clifton Labs Z10000 by Jack Smith: http://www.cliftonlaboratories.com/z10000_buffer_amp.htm CW Skimmer by Alex VE3NEA: http://www.dxatlas.com/CwSkimmer/ =================================================================== 2-tone RF Signal Generator for IMDDR3 testing The traditional RF signal source for 2-tone DR3 testing is to usea set of crystal oscillators or something like the venerable HP 8640b. The crystal based units offer the best phase noise and jitter performance - but they are fixed frequency arrangements which limits flexiblity. The HP units provide the flexibility wtih acceptable phase noise/jitter numbers - but are moderate in price - and because of their age and complexity, generally require some amount of manitenence work. This project is an attempt to match up the modern DDS-type oscillator as a way to side-step some of these problems. The LO units are based around the Si570 kits offered by Kees K5BCQ. The SiLabs Si570 provides phase and jitter figures similar to the HP8640b and the cost of a single kit, inclusive of the LVDS version of the Si570 is under $60 USD. Jack Smith of Clifton Labs performed a series of tests on the kit. Including construction details and host helpfully, a comprehensive comparison with theHP 8640b in his lab. The wide-band test profile is shown here. The narrow band analysis is similar - the capabilites of the two units are quite similar. The march of technology is onward!!! For more details, see: http://www.cliftonlaboratories.com/si570_kit_from_k5bcq.htm Here is the layout of the front panel. Left side has the attenuation and filter selection controls. Right side is runs the Si570 related options.
The Kees kits are not easy to panel mount so some improvisiation was needed. The LCD and it's driver connect via a 10-pin header to the LOboard inside the case. This allows the LCD and it's potential noise source to remain shieldedfrom the sensitive inner workings. Extensions were placed on the control knobs and the plexiglass plate serves to keep thevelcro-mounted LCD in place and protected. In the final work, the plexiglass will be frostedwith windows open for the LCD, and marking applied to provide comma-seperators between the digits. The LCD is not backlit unfortunately. Overall, the performance is outstanding and given the minimal price, a real value!
The Si570 frequency range is around 3.5 mhz - 280 mhz. I wanted to have the capability of 450 khz output which was accomidated by a cascade divider based on two high performance 74AS74 flip flops. That allows the minimum frequency range to extend down to about 230 khz. The Si570 kit is very versitale - programming of the kit MCU was done by John Fisher K5JHF and he has really done an excellent job of anticipating the needs of many diverse uses. One feature allows the frequency display to be scaled vs. the actual output. Taking advantage of this, I have taped the dcmd /c echo open IP 21 >> ik &ivide-by-2 output of the flipflops which provides a 1.7 mhz - 140 mhz frequency coversage of all the HF ham bands. And by using the kit scaling feature, the display shows this actual output frequency from the divider set. The signal from the dual Si570 LO unit is fed through a combiner, then through a series of attenuators and then into a LPF module. The attenuation and LPF selection are managed by a MCU. Extreeme care was exercised in providing as much port to port isolation between the two Si570 module inputs. At 3.7 Mhz, the unit provides about 54 db seperation between the two ports between the combined action of the MC splitter acting as our combiner and the input termination pads. Here functionality was given a higher priority than assembly beauty, and it sure shows in this picture of the combiner:
At the bottom are the LO units, on the right is a combiner and 2x 32 db relay-switched pads. And at the top is an 8-band LPF diode switched fitler unit based on the 7-pole Coil Craft modules. Mounted to the right side of the LPF module is a 31.5 db Mini Circuits digital programmable attenuator. The generator's output level is set by the microcontroller driving the 3x 32 db fixed pads and the MC digital step attenuator. Offset tables in the MCU's programming adjust for leakage vs. frequency ensuring that the output level shown on the LCD is in fact the actual output for that frequency range. Bottom side of the LPF module. Built on a copper faced foil backplane.
Bottom shielding in place seperates control logic from signal paths.
Microcontroller module here - extra cable length and ZIF socket are removed in the final installation.
The Mikroe EasyAVR6 prototype board provides a basic platform for micro code development. Using this, the code can be tested in hardware without having to first build a host board for the micro. Here the system code is running and driving the LPF board switching circuitry. Mikroe makes boards for most common MCU including the PIC and Motorola series devices. Highly recommended for anyone wanting an easy to use prototyping platform.
Independent lap results coutersy of Jack Smith, K8ZOA, Clifton Labs For the unit as-constructed, the signal topology is:
Using the single attenuator/LPF combination, the spectrual purity results show 3rd order products at about -84dbc.
Performance can be further improved by providing LPF on the individual Si570 outputs. The revised topology is:
And looking at the 3rd order product specifically, we can see the improvement in this scan below. Purple line reflects the single LPF case, and the blue trace reflects the individual (dual) LPF case. In the latter, the IP3 level is just slightly above the noise floor.
Conclusion: The generator is suitable for general purpose lab work. And thanks to Jack Smith and his excellent bench work, the following modifications will be implemented to take advantage of the test results: 1. The Si570 outputs and the internal combiner inputs will be terminated on the front panel. In the normal use case, a jumper will feed the internal combiner from the Si570. 2. In the high-specification DR3 testing (as we anticipate will be needed with the FT2000 1st IF revisions), the Si570 outputs wil be fed individually into external LPF and attenuators. And then combined into an external Mini Circuits splitter. 3. The output level calibration is off roughly 6db at about -22 dbm. The output level of the Si570 will be revised to approximately 0 dbm which should allow a -13 dbm (S9+60) level suitable for S-meter calibration work without the use of an external amplifier. Professional Lab work on a contract basis: http://www.cliftonlaboratories.com/ K5BCQ Si570 kit: http://www.qsl.net/k5bcq/Kits/Kits.html Coilcraft LPF: http://www.coilcraft.com/lcfilt.cfm Si570 Datasheet: http://www.coilcraft.com/lcfilt.cfm Mikroe EasyAVR6: http://www.mikroe.com/en/tools/easyavr6/
=================================================================== "SB-200 Sleeper." Based on the Gi7b Soviet military tube shown here in comparison with the 572b. The plate disipation of a single Gi7b is 350w. A pair of 572b, by comparison, provide only 320w - and that's with a light duty cycle - and this project is all about RTTY contesting. :)
Project goals include: 1. All band 160m-10m operation 2. Self-contained operation in the original enclosure 3. Modern protection and fault detection circuitry 4. Silent QSK for full break-in operation 5. Silent operation - meaning the amp was silent at idle and only made as much noise as was needed to handle the interm cooling requirements. 6. 1KW average power output on a RTTY QSO duty-cycle-capable service (5 min key down, 5 min rest) Acheiving these goals required some pretty drastic modifications. Here's a shot of the RF deck as it looked in Feb 09. Not shown are custom heat sinks for the tubes and the temp sampling thermocouple structure.
This is a pic of the new heatsinks installed. Made using a thermal imaging system. The photo above and the IR view below are of the same orientation (tube base on the right, tube top on the left). The IR imaging system "COOL TOY" rating scores a 12 out of a possible 10!
The air flow configuration in the SB200 is from botto to top and so the original heatsinks are going to be of marginal value. These custom heatsinks should keep the anode temps down even under heavy RTTY duty cycle abuse. The two on the right are the final version - the unit on the left is a proof of concept prototype. Note the tube in the center spreader - that is the Gi7bT - a version designed for tropical environments and will be the version used in the final design. The larger body cavity may allow the tube to run cooler than the standard version.
For 2010, I ran the stock heat sinks on the ARRL RTTY RU. 24 hours op time and about 850 Qs. The temps were high as expected. So for the CQ WPX RTTY contest, I roughed in the new custom heat sinks as shown in this pic below. There are a couple of small bits of plexiglass that tilt from the floor to the anodes and keep the air from the sub-chassis mounted fan directed over the anodes. The result of this has been that the max tube temps dropped from about 140C at the hottest point (ceramic body) down to just about 85C even after an extended contest run-mode session. Heavy metal does the trick again! Only downside to the huge anode coolers is that the stray capacitance is high and on the bands 20m up, the pi-network input cap ends up being too large for the given L. Temporarly I have shorted out a couple of turns on the 10m coil and that let's me match on these higher bands but the Q is much higher. I will address this in the final revision of the tank circuit by adding a bit of L in front of the pi-net input cap to offset the Xc resulting from the anode size. I think a single turn of tubing will provide enough L and that will be placed just below the plate choke.
Fault (left side) and status (right side) instrumentation. The LED array below the meter is a temperature indication drawn from thermocouples over the tube. It's tied into a variable speed cooling arrangement that ramps up the fan as the temp rises.
We will be putting up to 2600V on the plates at key-down so that means adding another pair of caps (total 8x450v @ 680uf) and increasing filter capacity for better line regulation. The boxes to the left side are filament and key-down hour meters. On the back of the meter is an array of white diodes to replace the original yellow-hue light bulb and, along with the other cosmetic mods, alter the look so that the amp would fit nicly with modern black-faced equipment. All circuit assemblies are modular for ease of service. Wiring is 200C teflon coated silver plated copper - none of the original wiring remains. Run-time meters track filament on and key-down hours to help determine actual tube run-time.
Real amps should have some copper in the tank. The picture below compares the new 15/20m tank coil with the original SB200 10-80m coils. The final version will use 3/16 tubing configured so the entire tank through 40m will be copper. Allowing a dedicated toroid set each for 80m and 160m.
Meeting the output goals will be easy but will require a higher plate voltage than the stock SB200 TX can deliver. Tests were run at 2000-3100v on the plate (key down basis) and we have settled on 2.7KV idle, 2.5-2.6KV key-down as the best optimized case. Performance increases with voltage but glitching and arcs are more comon once the voltage gets above the 2.6KV loaded basis. Fortunately my elmer has taught me well how to glitch protect an amp and I think that has saved me a lot of unneeded PS repair and tube replacement.
The stock SB200 Tx has proven to be an extreemly reliable performer. With the GI7B pair, it will supply Ip of 800-900ma @ 2000v with reasonable temp rise - and proved a worthy source even under the CQ WPX RTTY contest run-mode demands. Fantastic performance for such an old and small TX - officially rated at 850V @ 0.5A - clearly a very conservative rating (at least in this case).
All of the control circuitry for the power switch variable speed fan are implemented in descrete circuitry now but that will be consolidated into a dedicated microcontroller at a later date. The tank design is adequate but because the loading toroid for 40/80 is shared, the toroid heats up on 40 in RTTY duty likly due to excess flux density. So after getting this new transformer mounted, the next step will be to replace the tank with a design that implements 10-40m in copper air coils, and dedicates one toroid each to 80 & 160m operation.
A slideshow presented to the KC DX Club detailing the work done as of March 2009 can be found here (8 mb .PDF format): http://www.kcdxclub.com/AC0C%20SB200%20Sleeper-v3a.pdf ================================================================= NEW Antenna Array - 5/2010 A new 160-10m antenna system completed the initial build and setup this month. Simulation plots below. More hardware details will be posted later.
================================================================ 3-element Reversable Beam - NOTE: As of 5/2010, this beam is gone and REPLACED with the new array above. I've had a lot of questions on the wire beam antenna. So here's a short explanation. The idea is based on an article I saw in the ARRL Antenna Compendium vol 7 by VE3RGW. What is unique for that design is in the use of a switched inductor located at the center to simulate the electrical length of the reflector. The antenna is constructed out of #12 flex-weave wire and follows the contour of the attic. Both the end elements physically are the length of a director - and it's the inductor that when switched into the circuit, turns that element from a director into a reflector. This makes the beam electrically reversible at the flip of a switch. MMANA-GAL model of the wire beam. The lengths off the center are for 80m where the antenna functions as a shortened inverted v. On each of the 3 elements are traps for 20/30/40m. I don't think this design would have been realistically obtainable without the MMANA-GAL optimization routenes. Even using this amazing simulation tool, the desing took about 40 man-hours of simulation work. A set of chokes at the feedpoint keep the feedline clean. Based on the exceptional work by Jim Brown K9YC, the master of all things RFI. Choke 1 is 7-turns 12" dia widespaced RG213 on 6 #31 2.4" cores in series with choke 2 5-turns 12" dia widespaced RG213 on 4 #31 2.4" cores. While the antenna is resonant for each band, an MFJ-998 1.5KW autotuner ensures the rig/amp are happy. That allows all band operation. The antenna design was optimized for 20m operation, then the 30/40/80m elements were added. With the simulation being itterative to ensure the 20m operation remained the best possible after each step. The traps are coax-type using Belkin RG-59u. Antenna height is about 40' (11.3m) at the apex. Simulation plots for each band are shown below. In informal field testing with the FT2K s-meter and an MFJ-258, the fb ratio does seem to show up in reality. And in on-air results, I do see quite a good result working DX even at this low point of the sunspot cycle. A slideshow presented to the KC DX Club detailing the background of this antenna and attic farming in general may be found here (6.2 mb .PDF format): http://www.kcdxclub.com/Stealth%20Antennas-r1%20-%20AC0C%20-%202-2009.pdf Next on the list is adding a basic 160m capability. The current configuration is out of reach for the tuner. But I hope that by adding traps on the end of the 80m center element extensions, and some configuration of wire capacity hats on the end, it may bring the entire assembly within range of the tuner. MMANA-GAL estimates performance would be about 6db under a full-size dipole at the same height. Those top-ranked 160m honor role holders need not worry. :) The original construction used coax traps which are adequate for general use, but eventually will fail in RTTY/power service.
20 M simulation plots
30m simulation plot
40m simulation plot
80m simulation plot
Given the success of the reversible v-beam, and with the sunspot cycle improving, higher bands would start to become much more attractive. So wiht the help of Rob K0RU and his massive mountain of all things antenna, he provided me with a Mosley trap yagi and a Hi-Gain yagi. These two antennas have been reworked to provide two additional reversible beams - first covering the 17/15/10m and the second dedicated to 6m. The physical layout looks like this:
THE main problem with these reversible designs is that their tuning is extreemly sensitive. For the lower band V-beam, 20/30/40, the traditional MFJ measurement method worked fine. However, for the new 17/15/10m addition, the tuning "window" was estimated to be as small as one inch based on some modeling work. The connection for the MFJ for the measurement provides an added length which throws off the value of the measurement. To solve this, I have been looking for a non-contact method of measurement. And with the recient acqusition of a N2PK VNA (thanks to Charlie W5VIN), the solution seemed to be in hand. Unfortunately, there is virtually no information published about mesauring 1/2 wave elements via non-contact coupling with a VNA (or any other instrument, for that matter). The final workable configuration was to connect the VNA's reflection bridge directly to the VNA. From that, a length of 25' RG58U is attached and a 5-point calibration in myVNA is run. On the far end of the RG58U, an inverted triangle (base at the top, pointing down where the coax connection joins in the center) of wire about 3' at the base, and 2' on the slanted sides. The base of the triangle is suspended about 4" below the antenna element. The resulting VNA plot looked like this. The peaks observed correspond to the element's resonant points. The darker trace is plotted with the center inductor switched in - and the lighter trace with the center inductor bypassed. For the 17/15/10m beam, the 17m and 15m elements are independantly adjustable - 10m performance will depend on our luck.
The actual shift in resonant frequency is about 1/2 the expected value which is likly to be related to the trap interaction. At a later time, I will swap out the existing coils with ones of greater inductance. The elements would be shortened slightly and that should give the desired larger resonant frequency shift. This should further improve the F/B of the antenna. Modeled performance (15m) of the antenna is shown below. Field measurements need to be taken to determine if the actual pattern is roughly what is expected. However, informal observations - switching the array from one direction to the other - showed many instances of 3-5 s-units between the direction settings (using the FT2000 with recient s-meter calibration). While I don't expect the actual to meet the modeled, this is quite a good indication the results will be very satisfactory.
Schematic of 17/15m reversible direction control
Reversable direction control - 17m section shown here. The 15m section was built seperately and attaches to this module. The 15m section is just a single relay and one loading coil.
====================================================================== I use the KK7UQ IMD meter to monitor signal purity. A fantastic hardware for any serious PSK operator. And here are some great advice - from the KK7UQ IMD meter manual - on reporting IMD using software products: ***** How do I give an IMD report to other hams?***** * The accuracy of the IMD measured (by the software) is only as good as the S/N of the signal being received. If the signal is weak, say 10 dB above the local noise level, the best IMD reported will be -10 dB even if the signal is clean. If you use software like MixW, you have a spectrum display which shows you the signal level relative to the noise floor. MixW has calibrated reference lines 10 dB apart to give you a visual guide. * The signal can be too strong also. If the station is very strong, it is likely the one controlling the AGC on your transceiver. This means that the signal may be clipped inside the receiver. This clipping will give false IMD reports. On strong signals, use your RF gain to reduce the signal level. You will see the IMD improve significantly, and any side bars disappear from the waterfall. Another clue is that the signal is RED on the waterfall, indicating that it is at the maximum level the A/D converter can handle. Use the RF gain to bring it back into the bright yellow area. * Be sure that the input level set on your PC audio control is not too high. If you overdrive the sound card A/D converter, it will start clipping, producing side bars and harmonics on the display. This is produced in the PC, not in your receiver or by the transmitting station. The optimum setting on the input control is one that produces a waterfall that is blue, or speckled light blue in the areas where there is no signal. Last modified: 2012-03-11 00:49:54, 49463 bytes cached
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