2 Meter VHF Receiver


2 Meter Synthesized / Portable Receiver

By: Steve Hageman

 The 2 meter receiver shown built in both desktop and hand-held versions 

As seen on the cover of QST magazine, February 1999.


Thanks to the courtesy of the ARRL and QST you may now read the entire article on line (To Online Article)

 

Great News: As of June 1, 2005 Lansdale Electronics has announced that they are making the MC13135 and MC145170 replacement parts for Motorola. So this project is alive again! Please contact Lansdale at www.lansdale.com for price and availability.


The receiver is built from a Motorola single chip receiver IC, driven by a Motorola single loop PLL (1st LO drive). The receiver operation is controlled by a Microchip PIC16C73 uP (Source code available here). The PIC controls the LCD display, PLL and all the user interface including the rotary encoder used for tuning. The LCD displays the tuned frequency and signal strength in a bar graph format.

The receiver can tune the entire 144-148 MHz band with tuning steps of 5, 10, 100 and 1000 kHz steps (switch selectable). Scanning the entire band for signals can also be done in less than 4 seconds. The scanning mode works like most commercial scanners, that is it stops on any signal and only continues the scan after 2 seconds of silence.

In RS232 mode the scanner can be controlled by an RS232 link to any Windows 95 computer. The PC program can completely control the receiver (example screen shot) and adds memory functions and also allows computer controlled scanning. The PC program also has the capability of acting like a spectrum analyzer by continually scanning the entire band and displaying the strength of any signals found (example screen shot) .

The receiver can be built in the Handheld version or the Desktop version (minus the display, computer control only) using the same PCB by simply deciding which parts to include during assembly. Both versions can be built for RS232 control. A preprogrammed PIC16C73 is available from me, see below.

Specifications of the receiver are:


2 Meter Receiver Project FAQ's

Please e-mail with your questions and if you have found parts anywhere. That's how this all works, you share with me, I'll post it so everyone knows -- and I'll give you credit too!

 

Documentation:

Thanks to the generosity of the ARRL and QST, they now allow me to post the entire article, schematics, etc. You may now download the Schematic and parts list, along with the assembly information for the PCB here. Download 2_rx_article.zip

 

Parts Issues:

As with the Personal Network Analyzer Project, I will be keeping folks abreast of where to get parts for the project here.

1) A PCB is available for the project from FAR Circuits. Check with FAR directly please, as they supply the PCB's, not me.

2) A preprogrammed 16C73 PIC is available from me for $30 US Dollars. Shipping to the US of A (and Canada, Eh?) is FREE. Shipping to Europe is $5.00 (Via US Post Office Global Priority Mail). Shipping to South America is $10 US Dollars (Via anyway I think it will get there!). Sorry South America, the postal system down there just looses too much of what I send.

3) DC Kits lists the MC13135 on their web site. Try them at www.dckits.com. You might also ask about the MC145170 and the MPSH10 transistors.

4) Future (a big Canadian distributor, eh?) is not on the WEB (i.e. no search engine), but they do supply a lot of Motorola parts to the world. Give them a call at 1-800-655-0006 and see if they have the Motorola parts.

5) A free program called PartMiner is available from partminer.com. This nifty program will search a dozen sites for parts that you may need. Try it, it's how I keep up to date on what is available where. - Sorry they went belly up!

6) Newark has the MC13135P and MC145170D1 parts as of Mid January 1999. They have a $5 service charge for orders under $25. You can buy many of the other parts needed for the receiver from Newark also, such as Capacitors, Pac-Tec Case, Transistors, LM386, Speaker, 10 MHz crystal, Display etc. So if you shop carefully you should be able to 'Bundle' enough business with Newark to get over the minimum with no extra charges.

7) Well, it turns out that Digi-Key is no longer supplying the Toko TKS2715CT-ND SMT inductors that were used in the input filter (L1 and L2). Not to worry, the solution is to buy the exact same inductor (4 1/2 turn MC152 type) without the tuning slug, the part number for this core is TKS2709CT-ND. You will need two of these, one for L1 and one for L2. Then when you are buying the other inductor (L3) buy three of them (TKS2714CT-ND). When you get the inductors, take the brass tuning slugs from two of the TKS2714CT's and place the slugs in the TKS2709CT coils that do not have slugs. Viola... You just made (in a round about way) some TKS2715CT inductors exactly as specified in the article.

8) I slipped a digit! All Mouser capacitors listed that are 20 pF and under should have the prefix 141-100N2-XXXX, not 141-100N5-XXXX as printed in the article (cripes, it's February and already I've made my one mistake for the year!). Additionally, C3 was listed as 5 pF, this part has been discontinued by Mouser. An equivalent replacement is the 141-100N2-4R7D (4.7 pF, close enough for this application). Thanks Doug for pointing this out to me.

9) Bill found some reasonable sources for the 10.245 MHz, 2nd LO crystals (thanks for the help Bill!)

Crystek Crystals, 12730 Commonwealth Drive, Unit 6&7, Ft. Myers, FL 33913, 1-800-237-3061

They stock 10.245MHz xtals in HC49 holders for 32pFd load, 50 PPM at, 25deg. C. Price is $7.50 ea. with $25 min for out of town. If you want a custom ground crystal they are @12-$13 each.

JAN Crystals, 2341 Crystal Drive, PO Box 06017, Ft. Myers, FL 33906-6017, 1-800-526-9825

They do not stock 10.245MHz, but are ground to order. Price is $11.00ea. plus $3.00 S&H

 

Hardware FAQ's:

Here are the FAQ's as they relate to the hardware portion of the project.

1) Very detail oriented persons may notice that my article's parts list calls out for a specific values of inductance for L1, L2 and L3. Then they might notice that the TOKO description of these parts is always higher. What Gives? Well TOKO lists their inductance for the coil with no brass tuning slug, but they are sold with a slug. I listed the actual value of the inductance that the circuit was designed for (and what the specified coils are). The part numbers listed in the article are correct, the TOKO description is incorrect! They should really get a Agilent Technologies (Formerly Hewlett-Packard) LCR meter so they would know what their actual inductance values are!

2) Unfortunately at the last minute QST changed the schematic and swapped the labels for L3(VCO Coil) and L4 (Quadrature coil). The QST schematic and parts list agree, but not the PCB that I laid out for FAR Circuits. On the FAR PCB, please note that L3 is the Quadrature coil (a large shielded package). L4 on the FAR PCB is the VCO tuning coil (a small SMT package). This should not pose much of a problem as there is no way that you can confuse the parts, the Quadrature coil is 5 times the size of the VCO oscillator coil.

3) The MC145170 is available in many varieties. First are the package types: P is a leaded plastic part, D is a surface mount version (Don't buy the DT part, it's really small). The surface mount versions can be used in the FAR circuit board with the use of an Aries SMT to DIP adaptor socket that is available from Mouser (Aries # 535-16-350000-10). Motorola also makes a -1 (dash 1) version of this part. The dash 1 is a slightly higher frequency version of the part, an associate of mine tried this part on the FAR PCB and reported no problems with it. Motorola also advises me that dash 1 is backwards compatible with the non dash 1 parts and should be a drop in replacement. The exact part numbers that should work are: MC145170P, MC145170D, MC145170P1 and MC145170D1.

4) The MC13135 is also available in many varieties. First are the package types: P is a leaded plastic part, DW is a surface mount version. Unfortunately Aries does not make an adaptor for the DW package. If you find only DW parts the only option today is to use wire wrap wire to extend the leads to the leaded pattern on the PCB (keep the wires as short as possible). FLASH: The MC13135 just showed up on Motorola's discontinuance list, this means that by the end of 1999 the leaded plastic parts will no longer be available. Thank's loads Motorola :( If anyone knows of an adapter socket please let me know so I can post it here for everyone to see! Thank you.....

5) Where do the jumpers on the FAR PCB go? Click here to download a nice Acrobat file that shows the locations.

6) The battery in the portable unit could probably use more clarification as to charging. The battery specified is a 550 milliamp hour (i.e. the one 'C' rate is 550 mA) Nickel Metal Hydride type (in AAA format cells). Each cell has a nominal voltage of 1.2 volts, so 5 cells produce 6 volts. During charge, the battery will rise to about 1.4 volts per cell (or 8.4 volts) when fully charged. The 36 ohm / 12 volt charge I specified in the article produces a full charge in around 4 to 5 hours. The wall wart I used dips to about 11 volts at 100 mA so the setup I used trickle charged the batteries at about 140 mA when the charge starts, then drops to about 72 mA at the end of charge. These cells may be charged with up to 110 mA continuously without damage (C/5 rate). The setup I used 'taper' charges the batteries safely limiting the fully charged current to around 72 mA. At any rate the batteries should never be charged so fast that they get hot to the touch as heat will greatly reduce their life. If you are using a 12 volt wall wart and want a 12-14 hour charge instead, then limit the charging current to 55 mA (C/10) average. Probably a 100 to 150 ohm, 1/2 watt resistor will suffice for 12-14 hour charging .

7) It was brought to my attention that the speaker symbol was dropped from the QST published schematic. The parts list lists LS1 as a part and a really nifty Panasonic speaker, but no LS1 on the schematic. The speaker connects to the output (labeled "Audio Output") of the LM386 amplifier. You can also use any small 8 ohm speaker for audio that you may have in your *junk box* if you like.

8) In the articles conclusion I wrote that it is possible to add transmit operation by using a cell phone output stage. This is possible as mentioned, but I have no plans right now to implement this feature. If you are interested in doing this yourself, you will need to reprogram the PIC to change to the PLL to the transmit frequency, add a T/R switch to the antenna, squelch the receiver, rework the PLL some, etc. This is not difficult, but it will require some knowledge of PIC's, PLL's, Impedance matching, etc. If you want more information on cell phone output amplifiers, check the following manufacturers: Anadigics, Connexant, Triquint, Motorola, ITT or go to www.rfglobalnet.com to find an excellent industry resource for all kinds of wireless parts.

9) Bill reports: C32 (the PLL 10 MHz crystal oscillator frequency adjustment), Digi-Key part number SG10016-ND, is a bottom adjust trimmer. I drilled a hole in the PC board to gain access to the adjusting slot. Another choice would be the SG10015-ND, same value but top adjust. Center for the mounting holes is 1.27mm different but tabs may bend a bit to accommodate the difference. Thanks for the information Bill.

10) Bill asked about noise pickup, here is what I know from my prototypes:

A) I found that my display would cause some noise when placed really close to the receiver board. This noise was strongest around 145 MHz, and was not really apparent on all channels (kinda like you would expect from digital noise). I mounted the LCD in the portable case with an aluminum strap. When I grounded the strap to the receiver board topside ground plane with a short wire, the problem went away. Copper tape applied to the back of the display and grounded in the same manner would probably work as well, just be sure not to short out the display!

B) The other noise problem I discovered was pickup with the RS232 lines. This sounds more like a 'thump-thump' sound (i.e. you can hear the RS232 'polling' from the computer). This noise was audible on all channels, like you would expect from low frequency audio coupling. This turned out to be audio pickup. When I re-routed the audio volume control away from the RS232 cable this problem was eliminated. Another possibility is to shield the audio leads to the volume control.

 

Software FAQ's:

Here are the FAQ's as they relate to the Software (Firmware or PC Program) portion of the project.

1) The associated software (yes, and source code) is available free as HAG2MRX.ZIP at the ARRL Files Site. The program runs on Windows 95, 98 and NT and requires a standard RS232 port driven by a 16550 UART for proper operation (all name brand computers of 486DX and better should have this type of UART). The PIC Source code is available here also. The download from the ARRL includes the executable program, the Visual Basic 5.0 Source, The PIC source and the PIC HEX programming file (Useful if you can program a 16C73 from a HEX file).

2) If you unzipped the package with a DOS version of PKUNZIP (like version 2.04g), you may get the message that the install program can't find the file "two_meter.ini". This is because the DOS PKUNZIP truncated the file name on disk 3 to "two_mete.in_" (only 8.3 characters allowed). To fix this simply, rename the file on disk 3 to "two_meter.in_". Notice the trailing 'r', and install the program again. You must use the -D option when unzipping to recreate the directory structure.

3) Sometimes, it is reported, the install may take two tries to get the program installed (especially if the program updated any system files and rebooted the PC). Keep at it!

4) Overwriting of outdated files during install the should be safe as these files are all genuine, Microsoft files. If you don't feel safe about this, note the name of the file name(s) the install program want's to update, respond NO to the prompt(s). Then find these file(s), copy them to a floppy and reinstall the program. This way if anything goes wrong, you can recover from the problem.

5) You can uninstall the program by going to -> Control Panel -> Add/Remove programs.

6) Wouldn't you know it - I found two minor errors in the PC control program nanoseconds after I sent it to the ARRL :( #1 If you start a memory scan with no memory channels loaded the PC program will hang (to recover - do a CTL-ALT-DEL and end the task). #2 The lower left hand corner of the program window was supposed to show what COM port the receiver was found on. In version 1.0.0 it always says COM 1, even if the hardware was actually found on some other port. If you want a 90 k update to version 1.0.1 that fixes both these problems, then CLICK HERE TO DOWNLOAD. This is an update to the PC control program only, the PIC Firmware is OK. To use the update you still need to download and install the files from the ARRL (see direct link above). Then replace the TwoMeter.exe downloaded above with the one that the ARRL download installed.

 
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Updated - 1Jun05

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