this purpose, Type 1(a) and Type 1(b), in Figs. 7.3.3(a) and 7.3.3(b), respectively. Do not use the
noise-reduction capacitor C1, shown in Fig. 2(a), with either of these nets.
Type 1(a)
Type 1(b)
Fig. 7.3.3(a)
Fig. 7.3.3(b)
Although Type 1(a) nets use fewer components, Type 1(b) allows easier independent adjustment
of the net strength and time constant, as was the case with the original Type 1 nets. R2b is used
to vary the time constant, and the strength is adjusted using R4b. Convenient initial net
component values might be 20 ohms for R1b, which replaces the R1 resistor shown in Fig. 2(a); a
10k pot for R2b; 100 pF for C1b; 1000 ohms for R3b; and a 100k pot for R4b. In Type 1(a) nets,
the range of R1a might be up to about 100 ohms.
The general recovery tuning procedure (the use of additional nets with progressively shorter time
constants, and Type 2 nets) is as was described in section 7.3.2 above. If you use the Type 1(b)
nets for convenience in tuning, once the optimum strengths and time constants have been
established for the various parallel nets, you may then wish to calculate the corresponding Type
1(a) net component values in order to decrease the parts count in production. Although the PC36-
1 test board (described in section 10.) has not been specially drilled for these Type 1(a) and Type
1(b) recovery nets, you will find that there are quite a few extra or substitute holes in useful
locations.
If the use of these nets does not satisfactorily reduce your recovery problems over temperature
(and you have temperature-stable caps), try using a 15-ohm resistor between the detector and the
A1 input. If your results are still unsatisfactory, you have a detector which has inherent
temperature-dependent recovery problems. In our experience, this is only seen at RF input
powers at or above +5 dBm, but we have by no means tried all available tunnel diode detectors.
In such a case, the only solution would be to incorporate either sensistors or thermistors in
appropriate places in the net, e.g. in parallel with R1b. We would be interested to learn of specific
user experiences.
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