Using the PLJ-6LED digital display with the R4C

Floyd - K8AC All Messages By This Member #81669 I've been experimenting with the PLJ-6LED LED display with the R4C for a couple of days and have some issues.? Would like to hear what others have done to perhaps resolve these problems.? I'm feeding the signal at the INJ jack on the R4C directly into the counter and the voltage to the unit is 13.8 V.? ?On frequencies from 1.8 to 10 MHz, the display is stable and the frequency is accurate (checked against 10 MHz WWV).? On 14 MHz,? the frequency display becomes unstable, jumping around within a KHz or so of the correct frequency.? On 21, 24 and 28 MHz, the display is extremely unstable and the frequency shown is randomly up to several MHz off.? The R4C is properly aligned and I have full T4XC output on all bands when using the R4C to control the frequency.? I'm assuming that the signal level at the INJ jack for the higher frequencies is just not high enough for the unit to get an accurate sample, but haven't scoped it yet. ? I've played with the sensitivity/bias pot on the display board but was unable to improve things.? Even on the lower bands where the signal must be adequate for the counter,? adjusting the sensitivity/bias control does not seem to provide a linear control, but rather shows a sweet spot above and below which stability is lost.? So, I wonder what others have experienced with the counter on the higher bands?? If you don't see the same issue I'm seeing, did you use a buffer stage to feed the counter as the fellow who made the Youtube videos on the subject did?? I have two of the counters and they both behave the same way.?? ? Any suggestions appreciated. ? 73, Floyd - K8AC
Floyd - K8AC All Messages By This Member #81670 Just scoped the voltage at the INJ jack on the R4C across the bands.? As suspected, the voltage drops off the higher you go.? Here's what I see: ? 1.8 MHz - 1.96 VP-P 3.5 MHz - 2.08 VP-P 7.0 MHz - 5.9 VP-P 10 MHz - 3.96 VP-P 14 MHz - 1.82 VP-P 21 MH - 1.3 VP-P 28 MHz - 1.76 VP-P ? It seems that anything below 1.9 V or so is where the problem starts.? These voltages were measured at the INJ jack without the counter connected and going straight into the scope with no probe attenuation. ? 73, Floyd - K8AC
Frank KG9H Member Profile All Messages By This Member #81671 开云体育 I just sent you manuals. ? ? ?Frank Krozel ? ? ? ? ? ?KG9H Life Member, ARRL ? ? (630) 924-1600 kg9hfrank@...
Floyd - K8AC All Messages By This Member #81672 Edited Thanks, Frank.? Most of that I already had, but the charts showing the sensitivity by frequency was interesting.? Looks like there could be a loss of sensitivity as much as 10 dB between 160 and 10 meters.? I don't know if these units all come from a single manufacturer or if there are differences between different manufacturers.? Unless the counter is loading down the signal coming from the INJ jack, the stated sensitivity is far better than what I'm seeing. ? 73, Floyd - K8AC
Frank KG9H Member Profile All Messages By This Member #81673 开云体育 Floyd, cannot recall on mine, dont think I used any capacitor for injection for my C line. ? ? ?Frank Krozel ? ? ? ? ? ?KG9H Life Member, ARRL ? ? (630) 924-1600 kg9hfrank@...
jerry-KF6VB All Messages By This Member #81692 On 2025-01-06 14:18, Floyd - K8AC via groups.io wrote: Thanks, Frank. Most of that I already had, but the charts showing the sensitivity by frequency was interesting. This reminds me of a frequency counter I built in high school. It was a simpler age. Lots of 7490 decade counters. My counter was extremely insensitive. I tried to get it more sensitive by biasing the input near the TTL crossing voltage. That worked...to a point. If I got it right at the threshold, it would just go nuts. I came to understand that one of the main things that separates the men from the boys in the world of counters is sensitivity. I was recently tempted by a Chinese AWG with a built-in counter. I cancelled that order when I discovered that the counter needed a couple volts of input AC. Wound up buying an HP5385A. - Jerry, KF6VB
Robert N0GGO All Messages By This Member #81695 Hi Guys. I installed the aforementioned freq counters for displays on both a n T-4XC and an R-4C probably 10 years ago. At the risk of pointing out the obvious, you have to re-peak the pre-selector after band changes ( or large frequency changes). If the preselector is detuned, the injector signal is much lower. On my units I lost the display when I changed bands only to have the display return to service after the preselector was tuned. Other than that, they worked and looked great (matter of opinion , I know). Please forgive me if this is overly obvious, but I would have felt bad if I knew the answer and let you guys struggle lol. 73 & Good Luck, Bob. N0GGO
Floyd - K8AC All Messages By This Member #81698 Hi Bob.? Yes, I discovered that early on.? At 20 meters and above, however, peaking the preselector didn't solve the problem.? While I had carefully aligned the R4C using the Drake recommended technique (soldering in the resistors, etc.), I decided to revisit the alignment this time using Rob Sherwood's suggested technique.? After doing that, the counter works perfectly up to 10 meters, where the injection signal is still apparently too weak.? Next I'll try a buffer amp before the input to the counter.? At any rate, I suggest that anyone using one of these counters with the R4C use Rob's alignment procedure and resolve any issues you find along the way in that procedure. ? 73, Floyd - K8AC
Joseph KA3BWP All Messages By This Member #81702 Floyd, ? Have you seen this article? ? https://www.wb4hfn.com/DRAKE/DrakeArticles/C-Line%20Digital%20Display/C-Line%20Digital%20Disp.pdf ? JP KA3BWP
Floyd - K8AC All Messages By This Member #81709 On Tue, Jan 7, 2025 at 11:24 AM, Joseph KA3BWP wrote: Have you seen this article? ? https://www.wb4hfn.com/DRAKE/DrakeArticles/C-Line%20Digital%20Display/C-Line%20Digital%20Disp.pdf ? Yes, that was the first writeup I found when I was looking for something else at his site.? After trying the same module (10 years newer version) and having different results, I chose to post here to see if anyone else had actually tried it.? The author was apparently able to get adequate signal to the module through a 27 pF capacitor at the input. No such luck here.? ?An odd thing about the module he used is that the digits must have been a bit smaller than those of the current modules because the 6 digits of the newer modules will not come close to fitting the width of the dial opening in the R4C front panel.? ? No problem on the lower bands where MHz requires a single digit, but on the higher bands I'd be missing at least half of a digit in width. ?I chose to mount the module in an external case sitting on top of the receiver.? ? 73, Floyd - K8AC
Paul Christensen All Messages By This Member #81711 开云体育 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. ? ? 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.? ? 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.? ? Paul, W9AC
Gary WB6OGD All Messages By This Member #81723 开云体育 If you don’t really need to see the MHz,? you could tap the PTO signal, it is larger and is the same for all bands. 73, Gary? WB6OGD toggle quoted message Show quoted text On Jan 7, 2025, at 10:05?AM, Paul Christensen via groups.io <w9ac@...> wrote: ? 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. ? ? 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.? ? 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.? ? Paul, W9AC
Dieter Horst All Messages By This Member #81724 开云体育 The PTO needs very good buffering. Otherwise the signal drops and sensitivity is reduced significantly. I used an FET as a source follower with 50 ohms. So you can connect standard coax.? Of course to feed your FS4B, Gary! ? 73, Dieter DL5RDO Von meinem iPhone gesendet toggle quoted message Show quoted text Am 07.01.2025 um 22:23 schrieb Gary WB6OGD via groups.io <winbladgary@...>: ?If you don’t really need to see the MHz,? you could tap the PTO signal, it is larger and is the same for all bands. 73, Gary? WB6OGD On Jan 7, 2025, at 10:05?AM, Paul Christensen via groups.io <w9ac@...> wrote: ? 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. ? ? 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.? ? 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.? ? Paul, W9AC
Gary WB6OGD All Messages By This Member #81750 On Tue, Jan 7, 2025 at 01:51 PM, Dieter Horst wrote: Of course to feed your FS4B, Gary! ? ? Very good Dieter!? Others should build that and not buy the counter module..? hi hi. ? I just use the one bipolar buffer and I don't see it reducing the PTO level..? In fact I have reduced my PTO drive to reduce Drake spurs.. though I do have solid state mixers in my R-4B! ? I don't have these chinese counters but if they can work on the INJ signal (only like 50mvPTP IIRC) and not load that, they shouldn't load the PTO (3VPTP) much. ? 73, Gary WB6OGD ?
Frank Barnes All Messages By This Member #81755 I would appreciate someone posting the schematic diagram in an email, for a buffer amp that works with these Chinese counter modules. Thanks toggle quoted message Show quoted text On Wed, Jan 8, 2025 at 10:54?AM Gary WB6OGD via <winbladgary=[email protected]> wrote: On Tue, Jan 7, 2025 at 01:51 PM, Dieter Horst wrote: Of course to feed your FS4B, Gary! ? ? Very good Dieter!? Others should build that and not buy the counter module..? hi hi. ? I just use the one bipolar buffer and I don't see it reducing the PTO level..? In fact I have reduced my PTO drive to reduce Drake spurs.. though I do have solid state mixers in my R-4B! ? I don't have these chinese counters but if they can work on the INJ signal (only like 50mvPTP IIRC) and not load that, they shouldn't load the PTO (3VPTP) much. ? 73, Gary WB6OGD ? -- Frank Barnes W4NPN Chapel Hill, NC Grid Square FM05 Cell 919.260.7955
Floyd - K8AC All Messages By This Member #81763 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. ? ? 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.? ? 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.? ? Paul, W9AC ? 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. ? 73, Floyd - K8AC??
Gary WB6OGD All Messages By This Member #81764 I like to use the J-310/MPSH-10 buffer amp used in the old (now retired, NLA) NorCal FCC-1 frequency counter kit. ? Schematic is in the manual at: ? The same or similar circuit is used in many articles.? Works good on the INJ line. ? 73, Gary WB6OGD ?
Paul Christensen All Messages By This Member #81779 开云体育 Floyd, ? 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. ? ? Paul, W9AC ? toggle quoted message Show quoted text 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 ? 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. ? ? 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.? ? 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.? ? Paul, W9AC ? 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. ? 73, Floyd - K8AC??
Paul Christensen All Messages By This Member #81784 开云体育 P.S. ? I would first start with only Q1 to rule out any effect cable capacitance is having on the RF voltage level between INJ and the digital display.? The display spec sheet indicates that it should function with way less than you measured at INJ. If necessary, then add Q2. ? Paul, W9AC ? toggle quoted message Show quoted text From: [email protected] <[email protected]> On Behalf Of Paul Christensen via groups.io Sent: Wednesday, January 8, 2025 8:13 PM To: [email protected] Subject: Re: [DRAKE-RADIO] Using the PLJ-6LED digital display with the R4C ? Floyd, ? 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. ? ? Paul, W9AC ? 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 ? 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. ? ? 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.? ? 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.? ? Paul, W9AC ? 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. ? 73, Floyd - K8AC??
Mark - WB0IQK All Messages By This Member #81800 Floyd, The width of the display has not changed since I wrote the article many years ago. The unit does not touch the front panel but is mounted next to the inside panel behind the display plastic window.? Since it is mounted some distance from the front panel window, you can easily see the first and last digit by adjusting your viewing angle by moving your head left or right. I have my displays positioned slightly more towards the center of the radio giving preference to the last digit. I've installed maybe 10-15 of these in this manner and have had no issues other than I have had to play around with the value of the coupling cap. Using a scope I monitored the INJ level and used a cap that did not load it down. I've not had to use a buffer amp, but that would be a good fix and probably eliminate having to play around with cap values.? ? Good luck and be interested in what you end up having to do to fix yours.? 73's, Mark, WB0IQK ? ?

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