The Pictorial-Schematic diagram above is an example drawing, and is used with this tutorial for the purpose of illustration only. Component parts and cable connections may vary in each ISO-KIT. Similarly, some components displayed in the photos that follow may also vary in appearance.
When we receive the ISO-KIT of parts, we examine the parts and open the diagram. Look over the schematic and get an idea of how the parts should be arranged on the PC board (PCB). By look it over, we quickly learn that the interface that eveyone has been making appear so large and difficult, is not at all complicated. In fact, it is an easy, and straight-forward assembly that can easily be completed in an hour, and have you on the air with PSK31, SSTV, or Packet within an hour or two.
It only takes a few minutes to look over the drawing and become familiar with who's on first... and 'what's on third'!
Use a small tip (pre-tinned preferred), pencil type soldering iron (35-40 watt). If it’s available, use a controlled heat solder station. For instance, I use the Weller WLC-100 variable heat (controlled) solder station with an ST-1 tip installed, when building the pre-assembled sound card to transceiver interfaces. Keep tip clean, I use a small damp (with water, of course) sponge from Radio Shack to keep my tips clean.
THE CAVEATS!!! :
Without beating a subject to bits... and bytes, I want to drive home a simple statement, and request. If you are new to soldering, there is one cardinal rule. Make sure you do NOT overheat wires that are shielded. When soldering shielded wires, the center conductor may have a thin layer of insulation that can melt quickly and allow a short to occur between the center conductor and the shield. When this happens, there will be no output or the shielded cable will not perform the function for which it was intended.
Too much heat can be as damaging as not enough heat. As soon as the solder flows in the wire to wire or wire to connection joint, remove the soldering iron. Be sure to use a good rosin-core solder. DO NOT use acid core solder or cleaner.
As an added assist, I use a ''LUXO'' lighted Magnifier to view the small components, and solder traces.... as something happened to my eye-sight after I passed 60 years of age... a few years back.
AVOIDING RF FEEDBACK (SQUEALS):
While building PSK31, and SSTV, interfaces between PC sound card LINE IN, and LINE OUT to various HF and VHF transceivers, I've learned many valuable lessons. Some of these I'm committing to print to help you resolve a problem before it arises.
The first problem I encountered was when I had my computer too far away from my transceiver. I built the interface, and had long leads (over 3 feet) from the computer Line IN, Line Out, and serial comport (PTT control) to the interface printed circuit board. Then I had another 4 feet of cable from the interface printed circuit board (PCB) to the transceiver input/output (I/O).
This is where most RF problems occur. Although shielded, these long leads tend to capture stray RF and in turn, it would reach the microphone, or accessory I/O jack. Combined with the PSK31 audio signal, this RF component would become 'base rectified' in the transceiver audio circuits, thus creating a squeal in my transmitted (on air) signal. To circumvent this problem, I build all the leads from the Line IN, Line Out, and serial comport (PTT) to the interface PCB, as short as possible. A one to two foot lead length to the interface control box, on each Line and the serial comport is enough length. You’ll find that most computers have all the sound card jacks, and comport connections within a few inches of each other on the back of most PCees.
Using the same strategy for the PCB to transceiver input/output jacks, let's try to maintain these leads as short as possible, if possible, less than three feet long.
Another RF problem can occur when the interface is placed too close to the PC monitor (screen). Some stray EMF/RF can be induced into the lines or interface transformers and create noise to or from the transceiver. Avoid close proximity between the interface PCB and the PC monitor.
DC BLOCKING CAPACITORS (Tantalytics):
In most ISO-KITS that I distribute, I include a small, tantalytic capacitor (see photo below).
This is a 'polarized' capacitor (NOTE a plus + marking near the positive lead). The value of this compact sized capacitor is around 3.3 ufd, and may be as large as 6.8 microfarad (ufd). The voltage rating should be 25 to 50 volts.
The purpose of the cap is to provide DC isolation in the microphone input on transceivers which may supply a low bias voltage to excite 'electret' type microphones. If you find that you have one of these caps in your ISO-KIT, but are not using the microphone input for your PSK31 interface, then lay the small tantalytic aside or, at your option, install it in the transmit audio input to your transceiver anyway. If you elect to use this capacitor, BE SURE to install it with the 'PLUS (+) lead towards the microphone input or the transceiver audio input. The remaining lead connects toward the (RED) isolation (PSK31 Tx audio out) transformer lead.
UNDERSTANDING DIODE MARKINGS AND INSTALLATION:
To help you fully understand and identify the markings on the diode(s) used in the ISO-KITS, I've drawn a symbol and picture help the user relate the symbol definition to a pictorial of a diode.
SYMBOL
PICTORIAL
Some parts may vary from the original photo, or diagram. If your kit contains isolation transformers (and most all kits do), look at the color of the covering around the transformer winding. A ''RED'' tape/cover indicates a 1:1 turns ratio winding (600 to 600 ohms) (BUXFMR6K6). In most (all) applications, a RED transformer is used in the transmit (sound card OUT), to accessory, mic, etc... INPUT.
In many cases, the same type (color) transformer will be used in the accessory, Patch OUT, and Data Out ports. If your kit uses (extracts) audio from the external speaker jack (usually marked 'Ext Spkr'), one of the isolation transformers may have a 'BLUE' covering. This is a 1000 ohm to 8 ohm (BUXFMR1K8) isolation transformer. The 8 ohm side will be wired towards the external (8 ohm) speaker jack, while the 1000 ohm (side marked ''P'') is wired to the sound card tip and sleeve shielded 'LINE IN,' usually a 3.5 mm plug/jack. Please notice in the diagram(s) that the computer sound card is/must be isolated from the transceiver. This is the main purpose for using the "isolation transformers." Most of my diagrams reflect the correct measures for maintaining the isolation charactics of the interface.
To further define... the ground/shields on the transceiver side of the isolation transformers and Optocoupler may be considered one set (or side) of grounds, while the shield/grounds on the PC side of the 'isolation' transformers and Optocoupler are considered as a separate ground set.
The transformer may have a ''P'' stamped on one side of the red (or blue) cover. This ''P'' denotes the 'Primary' winding, or the first layer laid onto the bobbin/core. Some diagrams will note the position of the transformer in the circuit, relative to this winding (P) indicator.
NOTE; On most all isolation transformers, there are three leads on each side. The center lead from each side of the transformer is the ''Center-Tap'' and is NOT used. This center-tap may be cut off, or simply folded back onto the winding, and taped out of the way. Insure that it does not touch any other component or any metallic surface of the transformer.
In some interface part kits, there may be a small electrolytic type capacitor(s). One such kit is the Yaesu FT-847 (ISO-KIT-3). Notice the small print on the capacitor, and note the side/lead marked with the plus (+) sign. Remeber that this is the lead that goes to the radio Data I/O connector (yep, I had to use my handy magnifier to see it, but it's there).
On most diagrams that I provide for your PSK31 interface, I try to display the I/O (accessory, Mic, Data In/Out, Patch I/O...etc), port connector.
I draw these diagrams so the connector illustration shows the back side, or solder side view of the pins. Again, a ''caveat'' PLEASE; Verify the connections against your transceiver/radio manual. I AM NOT RESPONSIBLE FOR MISTAKES, ERRORS, OR OMMISSIONS!
There's always that one final little 'knat-bite' that is the ''got'cha'' for many new HAMs who've never had the chance to work with integrated circuits. I've drawn an IC (shown above) similar to the 4N25 or PS2601 that is used in the PSK31 interface. NOTE, that pin 1 is identified by a small, almost obscure circle just above the pin (1) location. I hope my illustration will clarify pin identification of the 4N25/PS2601 optocoupler/phototransistor.
PHOTO (Left); First we check the parts kit with the diagram to become familiar with each part and it location on the PCB. FYI, I always try to include more parts than are shown on the diagram, including wire and solder!
PHOTO (Right); Carefully follow the diagram and begin the assembly of our interface by dressing the first dressing (tinning wire ends with solder) wire ends first.
PHOTO (Left); OH NO!... I just hate it when that happens..... Have you ever installed a coax connector, and later realize you forgot to slide the retainer barrell on the coax first!!! Oh Geeze..! STAY ALERT !
PHOTO (Right) Plan the layout of the project PCB, as it is 2'' X 2''. The photos that follow may give you some ideas.
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PHOTO (left)
The first part of our ISO-KIT assembly is the layout and position of the components on the project board. The left photo is a rear view of the ISO-KIT with larger parts mounted. The right photo is a view of the project board front. How we arrived at the "front" of the PCB will become clear when we install the completed interface into the case. NOTE, The primary of each transformer is identified with a "P" on the primary lead side. The "P" should face the front of the PCB.
Photo (left) After the larger components are in place, I build the PTT driver circuit next. Make sure you have the six (6) pins of the 4N25 IC socket soldered to the PCB. Assemble the RS232 (usually the DB9 female) connector supplied with the ISO-kit of parts. A 20 inch shielded wire is used to attach the serial comport connector to the PCB. Wire and cable are supplied for all connector assemblies. The right photo illustrates the placement of the red LED transmit indicator and associated components. The right photo also shows how the comport connector lead is routed and connected. DO NOT OVERHEAT Components and shielded wire.
Photo left
is a bottom view of the PCB area around the 4N25 optocoupler PTT circuit. NOTE that all PCB will come with traces cut around the outer traces to allow more island connection solder pads.In photo right, the wire ends that are used to connect to the MIC connector, or accessory plug(s). This is an important part of the ISO-kit, as it is the main cable to the radio for data input/output and PTT. In some cases where RCA type phono connectors are used, a separate shielded wire and connector may be employed. In the right photo, there are two separate wire pairs. Each of the two pair has a separate shield. There is one drain or ground/shield wire. Looking at the right photo, viewing Left to Right, the wire colors are as follows: Left wire, horizontal is the SILVER (shield/ground) wire, the second wire from the left is "GREEN" and is used for RECEIVE audio from the radio into the interface. The third wire from left is WHITE, and is used for TRANSMIT audio TO the transceiver. The forth wire from left is RED and is the PTT + or hot lead. The fifth wire from left, is BLACK and is the PTT – minus (-) or ground lead.
Photo left gives an indication of component and wire placement. Note that in ISO-kit interfaces that utilized the accessory ports on some transceivers, the left (blue) "BUXFMR1K6" transformer may be the same as the (red) "BUXFMR6K6" transformer on the right. In the ISO kit interface which uses the MIC I/O, the pot will be a 1K or 2K potentiometer. Where higher level audio is required to drive the transceiver, e.g. the transceiver accessory data I/O ports, the pot will be a 25K to 50K
potentiometer. Once installed, the one-turn pot should be set to center of its range. This pot will be used only as a coarse adjustment. Fine tuning, or level adjustments are made using the software level control in your PC. In photo right; Notice the two jumpers across the PCB. These two (bus) jumpers connect the two outer leads of each transformer together to form a common connection for the shield lead to the transceiver, and on the primary side, the shields of the sound card leads.
NOTE: In NO case are the primary and secondary leads connected together on the PCB !
Photo left; Note the sound card lead connection at the PCB, to the end of the 27K resistor. The resistor value will vary between ISO kit types. Photo right; the shield of the sound card lead is connected through a hole to the "bus" lead jumper. NOTE the notches on each side of the PCB, see next photos for detail.
Photo left; Now you see where the front of the PCB comes in. Note the red LED position reference the "front" of the case/cover. Photo right gives a better view of the LED related to the lens location. The purpose of the "notches" in the PCB now come to light. FYI, I also drill a hole in some PCB instead of notching the PCB. The Sticky-back VELCRO is used to hold the PCB in place. It also keeps the PCB in place while the case screws are being inserted. Notice the 3/8" cable exit hole at rear.
Photo left; With the completed interface in place, and the red lens installed, we now take it for a test drive. Follow the level setup procedures that apply to your specific PSK31 or SSTV software. Photo right; As a rule, on interfaces that are pre-assembled, I label the leads with a definition that identifies their respective target jack or I/O. For your own sanity, if you label the sound card LINE IN plug with a YELLOW label or color, the other lead (LINE OUT) will be easy to identify. Once you have the coarse level set, install the top cover for your ISO-KIT interface and go have PSK31 fun.
73 deBuck Rogers K4ABT
PHOTO (Left) Finished, as in "Completed"... and ready to plug and play. Set the levels and install the case.
PHOTO (Right) The optional $5.00 case has a red lens face that allows the transmit LED to be easily seen.
Aaahhhhhh success is so sweet. On the air with one of many FREE programs for PSK31. Shown here is a screen shot of WinPSK, a program written by Moe Wheatly AE4JY.
Need a great PSK31 program? CLICK HERE to download WinPSK version 2.08.
The file WinPSK208.zip (630K) contains all the files needed to run the WinPSK program as well as online help.
All the files should be placed in the same directory, for example: C:\Winpsk . No setup program is necessary.
My goal is NOT to sell an interface parts kit, but to help all hams get into PSK31, as I feel that it is one of the most attractive and enjoyable digital modes I've yet to witness in over 55 years as a HAM. PSK31 is truly a mode that enables HAMS to communicate one on one, as well as in round-tables, using nothing more than your PC sound card, this simple interface, and your transceiver, be it HF SSB or VHF/UHF FM.
All ISO-KITS are $25 dollars each. Price includes the ISO-KIT-CASE, and postage & handling USA ONLY! Priority Mail.
Foreign orders; ADD $15.00 Shipping and Handling; Total ISO-KIT, CASE, and S&H is $40.00
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