Technical Bulletins
This page carries a series of articles providing guidance and information on applications and enhancements for our kits.
Index
TB-01 Extending the Frequency Range of the FD-01 and Minicounter
TB-02 Optimising the AGC Attack Time of the T-1
TB-03 Interfacing the FD-01 to the T-1/C-1 Combination
TB-04 Using Commercial Filters With the T-1 Main Board
TB-05 Minicounter Drilling Template
TB- 01 Date: 21 May 2004
Title: Extending the Frequency Range of the FD-01 and Minicounter
Scope
This bulletin applies to FD-01 Version 1.0 and Minicounter up to Version 1.1
Description
The FD-01 and Minicounter were originally designed for the measurement of RF frequencies spanning a few 10's of kHz to 100MHz. Both share a common input circuit. By changing the values of two components, a useful increase in frequency span may be obtained extending the upper limit to about 135MHz (600mV RMS input) and the lower limit to about 100Hz (600mV RMS input). The modification involves changing the bias resistor value on the MPSH-10 bipolar stage to 68K and increasing the value of the inter stage coupling capacitor to 100nF
Modification
To reduce the risk of damage to the PCB through plated holes on assembled kits, we recommend that this modification is carried out by leaving existing components in place and soldering new parts on the underside of the PCB as follows;
Key: FD-01 Parts (Minicounter Parts)
In parallel with R8 (R6) solder a 220K resistor. (Increases upper frequency limit)
In parallel with C17 (C2) solder a 100nF ceramic capacitor. (Reduces lower frequency limit)
Conclusion
This modification provides a useful increase in operation range. Subject to successful validation a design change will be incorporated into later kits.
Acknowledgement
Our thanks to Matti Niskanen, OH2CF, of Finland for providing us with details of this change.
END
TB- 02 Date: 12 October 2005
Title: Optimising the AGC Attack Time of the T-1
Scope
This bulletin applies to the T-1 Main Board Version 1.0 upwards.
Description
The T-1 employs a highly effective Full Wave detection AF AGC system. This approach was adopted over IF derived schemes to provide a design that is reproducible, is not critical of layout and does not require screening. The single drawback of AF AGC schemes when compared to IF derived AGC is that the response (attack) time is slower. However with simple optimisation, an excellent AGC performance can be achieved. This Technical Bulletin describes a simple technique for optimising AGC attack time and provides a default component value for those wishing to make a direct substitution.
Background
The AGC attack time is easily assessed by tuning the T-1 very quickly across a strong signal or alternatively sweeping the T-1 receive frequency with a signal source. In both instances a slow attack time will produce an initial brief burst of higher level audio as the signal is swept. With the default components supplied with the kit, this effect will not normally be evident when listening to a fixed frequency although it may be noticed when tuning quickly or during noise bursts. Reducing the AGC attack time correspondingly reduces this effect.
The critical AGC timing resistors are mounted as plug in parts in SIL socket strip on the T-1 main Board. The functions are as follows;
R71 AGC Attack time
R73 Slow AGC Decay time
R77 Fast AGC Decay time
Modification
The AGC Attack time is reduced by reducing the value of R71. If R71 is too small then AGC overshoot will occur, this is evident as "pumping" in audio level on received signals as the AGC tries to over compensate. To determine the optimum value of R71 for your configuration proceed as follows;
1. Ensure that the AGC threshold and Gain are set to provide an AGC operating range that suits your preference.
2. Remove R71 and temporarily replace it with a small 10K pot (e.g. Cermet). Discarded component leads soldered to the wiper and one end of the track will allow the pot to be plugged into the R71 position.
3. With a trimming tool set the pot for maximum resistance and tune theT-1 to a strong SSB or CW signal. Reduce the value of the pot until AGC overshoot is evident (a "pumping" of recovered audio level). Now increase the pot until the overshoot ceases, allowing a slight margin above the pumping threshold. Sweep the T-1 using the techniques described above, to confirm that the attack time has improved.
4. Remove the pot and measure the resistance between the wiper and track terminal used during the test. Select a resistor that corresponds to this value and insert into the R71 socket.
5. Re-confirm AGC performance.
Default Value
A value of 1K for R71 will in most instance provide a close to optimum performance.
Conclusion
This modification provides a useful improvement in AGC attack time over that given by the the 10K resistor supplied in the kit for R71. Subject to successful validation a component change will be incorporated into later kits.
END
TB- 03 Date: 12 October 2005
Title: Interfacing the FD-01 to the T-1/C-1 Combination
Scope
This bulletin applies to FD-01 all versions, T-1 v1.0 upwards and the C-1 v1.0 upwards.
Description
The FD-01 Transceiver Display is designed as a versatile display module that can be easily applied to many receiver or transceiver designs. The features of the FD-01 can greatly simplify the mechanical construction of new equipment and enhance existing designs, commercial or otherwise. The Technical Bulletin describes how the FD-01 can be combined with the T-1, C-1 pair to provide a highly integrated transceiver display that removes the need for additional mechanical metering or indicators in a transceiver application.
Background
The FD-01 is controlled by grounding the function select pins, these set the functionality of the FD-01 and the format of the displayed information. The C-1 controller is also operated by grounding control pins, these conditions are interpreted by the C-1 to produce command signals for the T-1 that are passed over the 16 way ribbon interface. Switching of FD-01 and C-1 functions is easily carried out by commoning controls and using rotary switches for selection. A schematic suitable for most application is given at the end of this Technical Bulletin, this is easily adapted to suit other configurations or incorporate additional features if required.
The interface scheme outlined in the schematic provides the following features;
| Control | T-1/C-1 | FD-01 | |
| Mode Switch | LSB | LSB Mode | LSB Display |
| USB | USB Mode | USB Display | |
| CW Wide | CW Mode Wide Filter | CW Display | |
| CW Narrow | CW Mode Narrow Filter | CW Display | |
| AGC Switch | AGC OFF | AGC OFF | |
| AGC Fast | AGC Fast Decay | ||
| AGC Slow | AGC Slow Decay | ||
| AGC Hang | AGC Hang Mode | ||
| Tx/Rx Control | High | Receive Operation | Rx Display/S-Meter |
| Low | Transmit Operation | Tx Display/Bar Meter |
Interface wiring details in pdf format here; Interface.pdf
END
TB- 04 Date: 30 December 2005
Title: Using Commercial Filters With The T-1 Main Board
1. Scope
This note describes how to interface commercial crystal filters to the T-1 Main Board.
3. Modifications
3.1 Filter Matching
Commercial filters generally require an input impedance of several hundred Ohms. The filter impedance is normally given on the filter. In this example we will assume a filter impedance of 500 Ohms. This needs to be matched to the 50 Ohm main filter ports of the T-1 using small wideband transformers. We recommend the use of FT34-43 toroids for this application.
Turns ratio = SQRT(500/50) = 3.16
This is matched closely by windings of 6 turns on the 50 Ohm side and 19 turns on the 500 Ohm side. Two transformers need to be wound, one for each side of the filter. The 6 turn winding should be soldered into the signal ports of the FL1 and FL2 connector positions on the main board. Be sure to use the signal terminals and not the filter select terminals of FL2. One end of each of the 19 turn winding should be soldered to ground in the clear area provided in the filter zone. The other end of the 19 turn winding is connected to the respective filter port (filter orientation is not important as lattice filters are bi-lateral elements). The filter can be mounted either by carefully drilling holes in the filter zone of the T-1 board or by using solder tags secured to the filter studs and then soldered onto the clear area.
3.2 Tail End Filter
The T-1 IF is a relatively low noise design and can be used successfully without a Tail End filter. To bypass the Tail End filter insert a wire link between pins 2 and 3 of the Tail End filter socket.
If you have two spare LSB carrier crystals you could use these to make a simple tail end ladder filter. The design impedance should be 250 Ohms and bandwidth around 3kHz. At 9MHz, a single 68pF capacitor from the centre junction of the two serial crystals should be about right.
3.3 Carrier Oscillators
The serial inductors on the USB and CW carrier oscillators should not be fitted. On each of these oscillators solder a wire link from the crystal side of the socket to ground and a link between the trimmer side of the socket and the hot end of the crystal. This will place the trimmers in parallel with the crystals allowing easy adjustment.
END
TB- 05 Date: 21 July 2006
Title: Minicounter Drilling Template
1. Scope
This bulletin applies to the Minicounter kit and the Varitronix MDLS16265 16x2 LCD
END
