Parts and Hardware Resources for RDF Home Builders

Sources for the Roanoke Doppler project

Complete construction plans for the Roanoke Doppler are in Transmitter Hunting---Radio Direction Finding Simplified (THRDFS). At this time, there is only one source of printed circuit boards for the display unit and antenna switcher.

FAR Circuits -- Fred Reimers KF9GX, 18N640 Field Court, Dundee, IL 60118, farcir@ais.net or http://www.farcircuits.net (847) 836-9148. Users have reported errors on older versions of the display boards. They have been corrected in display boards now being shipped. FAR Circuits also has a circuit board for the Wide-Range Antenna Array. There is a minor correction to the marking on this board.

Over the years, there have been several other sources of Roanoke Doppler circuit boards and kits. The following list may help you identify these legacy boards/kits. Links to documentation are provided where available. If you have Roanoke Doppler board/kit documentation that I do not have, please advise by e-mail.

Directional Systems -- Boards, kits and assembled units sold by Jim Sorenson KA4IIA in Conyers, GA. No documentation available.
"Fremont Board" -- Single board with display LEDs in one corner. A 1992 project of West Valley Amateur Radio Club in Fremont, California. Project leader Greg Bassett KJ6EP. Layout by Kevin Smith KK6VF, whose callsign is on the board. Later sold by Valid Link in Santa Clara, CA. Documentation is here.
"Greany Board" -- Single-board design sold by Ed Greany KB6DOL of Corona, CA. Documentation is here.
DF Systems board -- Stephen Douglas K6HZT of Sacramento, CA and Marsh Wildman sold single-board design under the company name DF Systems. Complete documentation is not available, but this errata document appears to apply to the DF Systems doppler.
"Lewis Board" -- Single-board design sold by Tom Lewis AB5CK of North Richland Hills, Texas. No documentation available.
"Mitchell Boards" -- Two-board design sold as "Roanoke Doppler Plus" by Marty Mitchell N6ZAV. Boards fit into the same enclosure as used in THRDFS. Has a data port with serial bearing output, but this is NOT the well-established Agrelo format. Documentation is here.

Disclaimer: The information above, and elsewhere on this page, is provided for the convenience of readers only. These suppliers are independent entities. They have no business association with Joe Moell or Tab/McGraw-Hill. A listing on this page does not constitute endorsement of products.

Sources for RF attenuator projects

Resistive RF attenuators are best suited for mobile HF and VHF T-hunting with directional antennas such as loops, yagis and quads. Pete Ostapchuk N9SFX sells parts for resistive attenuators, including a 6-section enclosure machined from 6061-T6 aluminum bar stock and engraved with attenuation values. Also available from him are switches, resistors and connectors. Plans for his project are in QST Magazine for May 1998. Send e-mail to n9sfx@aol.com for details and prices. The above disclaimer applies.

Another source of resistive RF attenuators is National RF, Incorporated (formerly Radio Engineers) of San Diego, CA.

For on-foot VHF/UHF "sniffing" and international-style foxhunting with a beam and handi-talkie or scanner, an "offset" or "active" attenuator is better because it eliminates the problem of signal leakage directly into the receiver's case. Plans for an active attenuator are at this Homing In site, click here. Parts are available at local suppliers, including Radio Shack.

Sources of PIN type RF diodes

For maximum receiving sensitivity and minimum problems with cross-modulation, good RF PIN diodes must be used in hard-switched dopplers such as the Roanoke Doppler. Breakdown voltage and power rating of the PIN diodes are not important in low-level receiving circuits. (You aren't going to transmit through the switcher, are you?) For low loss and good sensitivity, the diodes should have low RF resistance (Rs) at the expected forward DC bias current (7.5 mA for the wideband switcher). They should have low capacitance (Ct) at the reverse bias off-state voltage. Effective carrier lifetime and reverse recovery time (Trr) should be short. (PIN diodes with long carrier lifetime are ideal for current-controlled RF attenuators, but that's not what we want in this application.) Keep the diode leads very short to minimize inductance and make sure signal path lengths, including diodes, are equal for all elements in the array.

Suitable PIN diodes include:

Narda KS3542 -- DO-34 package, click for data sheet. A ham with a supply of these diodes has offered to make them available in small quantities to home builders of RDF equipment. Send e-mail to me for more information.
Philips NTE555 or ECG555 -- "Replacement" type semiconductor available at local electronics parts houses all over the country. Even some giant computer stores such as Fry's Electronics carry NTE parts. Priced $1.50 to $2.00 each. This is an older part with tab leads and unspecified series RF resistance.
Agilent Technologies (formerly Hewlett-Packard) surface-mount PIN diodes -- Surface-mount parts are best if you're building a doppler for UHF (400 MHz and up). Try Arrow Electronics, a major parts distributor in in Melville, New York. The Agilent HSMP-3892 or HSMP-3893 are good choices for a series doppler switcher such as the wideband array on this Web site. On the other hand, the HSMP-3820 is optimized for a shunt switcher such as the one in THRDFS.
Motorola MPN3404 -- In TO92-style plastic package. Advertised price is five for $3.50 at Dan's Small Parts and Kits, Box 3634, Missoula, MT 59806-3634 (406) 258-2782.
TRW A5S303 -- Axial lead device formerly available from Tanner Electronics in Carrollton, TX (214) 242-8702. Does anyone have a new source?
Agilent Technologies 5082-3077 -- Axial-lead low-Rs device available from Newark Electronics. Newark also carries Agilent 5082-3081 and 5082-3080, which are long-carrier-lifetime parts intended for variable RF attenuators and thus not suitable for doppler switches.
Motorola MMBV3401LT1 -- Surface-mount replacement for the now-discontinued MPN3401. Available from Motorola industrial distributors. Not suitable for perf-board construction.

After I bought some Motorola PIN diodes from Debco Electronics, I mentioned their availability in Homing In for April 1995. A reader wrote to me after publication to say that Debco was astonished at the response. The order-taker said that they hadn't sold a PIN diode for over a year and then after the article came out they began selling like hotcakes. Who says hams don't build nowadays?

Other Sources of RF Parts

Hard-to-find RF parts such as air variable capacitors for tuning HF loop antennas can sometimes be found at dealers of "overstocked" or "industrial surplus" components. Here are three to try:

Bogdan Electronic Research & Development (Jim & Carolyn), PO Box 62, Lakewood, CA 90712, (562) 634-0911. They sell RF parts by mail and are often at southern California swap meets, too. Note: Jim says that the margin on small quantities of RF parts is so low that it's not cost-effective for him to return calls. (I know the problem!) Therefore, please use e-mail or call back to catch him or Carolyn "live" on the phone if you get a recording when you call.
All Electronics, PO Box 567, Van Nuys, CA 91408.
Alltronics, 2300 Zanker Road, San Jose, CA 95131, (408) 943-9773.

For more information about sealed RF "piston" trimmer capacitors and sources, see the Shrunken Quad page at this site.

Ferrite beads and cores for the dual-polarization quad and other RF projects are available by mail order from Amidon Associates.

ByteMark Corporation, 7714 Trent Street Orlando, FL 32807 (407) 679-3184 also carries Amidon ferrite components and has technical information about Amidon ferrite and iron powder products on its Web site. In addition, ByteMark sells a Windows-based program for calculating the turns for coils on various Amidon cores.

The Philmore line of packaged electronic parts includes unusual items such as Amidon T50-6 cores (used in the ATX80 80-meter fox transmitter), International Rectifier HEXFETs, MPF-102 JFETs, etc. Unfortunately the Philmore Web site does not have a complete product list, but it does include a list of local distributors of these parts.

Crystals for 80-meter foxboxes are available from Brian Carling AF4K in Sanford, FL. He also sells some crystal-can oscillators that may be suitable for building offset attenuators.

Jerry Boyd WB8WFK provides this feedback on ON7YD's Fox Transmitter for 80 meters (ATX80), which was featured in 73 Magazine for November 2000: "Motorola MC14001B Quad-NOR ICs from Radio Shack (part number 276-2401) didn't work. The oscillator would not start properly. I tried 6 different ones and they all acted the same. I put in an old Fairchild CD4001B Quad-NOR and now it works with no problem. I downloaded data sheets from the manufacturers' Web sites and the internal schematics are indeed different." Fairchild ICs are available from many suppliers, including Digi-Key. KØOV's six transmitters use Signetics (Philips) CD4001B's packaged by Jim-Pak and sold by local parts suppliers nationwide -- they all work fine.

Sources for building polar-plot bearing readouts

I have many requests for sources of unusual electromechanical parts used in two-dimensional bearing indicators such as the KK6CU motorized quad, the WB8WFK and KD6IFZ computer displays, and the NØMKJ Foxcopter. (See the Homing In Index page at this site for articles describing these RDF systems.)

For (relatively) inexpensive surplus sine-cosine potentiometers as used in the KK6CU motorized quad, try Servo Systems Company, 115 Main Road, PO Box 97, Montville, NJ 07045, (201) 335-1007, in USA (800) 922-1103. The last catalog I received from this company included sin-cos pots by Litton, Duncan, N.E.I., Samarius, and Gamewell. There were continuous turning and single-turn models with prices from US$18.50 to $69.50.

For a "Cadillac" system, check out these contactless sin-cos resolvers using internal magnets and Hall effect sensors, designed to be rotated at up to 10,000 RPM: Elweco Incorporated, PO Box 909, Painesville, OH 44077-0909, (440) 254-1716.

Small industrial rotary joints (slip rings) in the $30 price class are suitable for low-voltage uses. NØMKJ used one of these for the two-meter coax feed in his Foxcopter. They are available from McMaster-Carr Supply Company, PO Box 54960, Los Angeles, CA 90054-0960, (310) 692-5911.

Another promising source of rotary joints is Mercotac, Incorporated, 6195 Corte del Cedro #100, Carlsbad, CA 92009, (619) 431-7723. Unfortunately the Web site does not list prices. If you use one of these products in your RDF system, please let me know how it works and what it costs.

Inexpensive electronic compasses with digital output (Vector 2X series) are manufactured by PNI Sensor Corporation, formerly Precision Navigation Incorporated. They are sold by Jameco Electronic Components, 1355 Shoreway Road, Belmont, CA 94002, (415) 592-8097, in USA (800) 831-4242. They are also sold by JDR Microdevices, 1850 South 10th Street, San Jose, CA 95112, (408) 494-1400, in USA (800) 538-5000.

From Peter PB2RDF comes this suggestion for a source of obsolete and out-of-stock electronic components for replacement or for older designs: 1-Source Electronic Components, 591-B Bicycle Path, Port Jefferson Station, NY 11776 (800) 966-8826 or (631) 642-2479.

Also see these Homing In site pages for specific project parts information

If you discover a good source of unusual parts for RDF homebrewers, please e-mail me.

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This page updated 24 October 2016