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Re: Using the PLJ-6LED digital display with the R4C

 

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Floyd,

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WB6OGD pointed to a good go-to reference from Elecraft.? Have a look at the schematic on p. 27 and refer to Q1 and Q2.? Q1 (J310) has a gain less than unity as a source follower.? However, it¡¯s then amplified by Q2 (MPSH10) in a collector-feedback circuit formed by R3/R6.? Install at the INJ point.? Use capacitive coupling from the Q2 collector to your new digital display.

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Paul, W9AC

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From: [email protected] <[email protected]> On Behalf Of Floyd - K8AC via groups.io
Sent: Wednesday, January 8, 2025 3:38 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] Using the PLJ-6LED digital display with the R4C

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Possibly consider a J310 JFET as a common-source amp placed right at the source of the INJ jack. Resistors chosen for a gain of A = 2 (6 dB) to get over the minimum RF sample voltage requirement. ?

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The JFET unloads the INJ line to the Hi-Z gate and that isolates the INJ source from cable capacitance to the freq. counter.? With adequate PS decoupling, probably a half-dozen parts are needed, mounted either on a 5-6 lug terminal strip or Vector board.?

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The common I.F. output buffers often seen are common-drain source-followers with a gain of less than 1.0.? That won¡¯t work in this instance to solve the problem.?

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Paul, W9AC

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That sounds like the solution, Paul, but I'm afraid I'm not capable of doing that probably simple design.? Can you point me to an existing example, or, do a simple design ?? Not sure why I seem to be the only one who ever had a problem with the available INJ signal level, but maybe others haven't actually tested their configuration on 10 and 15 meters with the T4X connected to the INJ cable.? Without that connection, the signal level is adequate to provide a stable readout in my case on the highest bands.

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73, Floyd - K8AC??
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