Frog Sounds 40m transceiver kit

Discussion in 'QRP Corner' started by K5DH, Feb 6, 2016.

ad: L-HROutlet
ad: l-rl
ad: l-gcopper
ad: L-MFJ
ad: abrind-2
ad: Left-2
ad: Left-3
ad: l-BCInc
ad: QSOToday-1
  1. K5DH

    K5DH Ham Member QRZ Page

    Have you seen the little Frog Sounds 40m transceiver kits on eBay? A friend alerted me to their existence and I had a look. The pictures and description looked promising and the price was only about $13 ppd. I figured for that little money I couldn't go wrong, so I placed my order. A scant few days later, a li'l package came in the mail from China.

    The circuit board is nicely made, with plated-through holes and readable silk-screening. No required parts were missing, but there were a whole bunch of extra resistors, caps, and diodes (let's call 'em "spares"). There are no surface mount parts, only old fashioned through-hole parts. It's all pretty small, though, so you'll need a soldering iron with a tiny tip.

    The documentation ain't so great. The schematic is readable, but they don't use "normal" component designations like I'm used to. The parts list is "sort of" complete. There are two toroids to wind, but no data is given on how many turns or what type of core they are! A few minutes of internet research turned up that info: L4 is 8 turns on the all-black T37-43 core, and L5 is 14 turns on the T37-2 core with the red paint on it. There was also no indication on which way to install the bi-color LED. Back to the internet to learn that the shortest lead is green, the middle-length lead is red, and the longest lead is common.

    The resistors are not marked using the "normal" four color bands. They use the Chinese system with five color bands. Best to use your Ohmmeter to figure out what you're looking at.

    Assembly took about 1-1/2 hours, the big slowdown being the winding of the two toroids. No issues with the assembly process. The hardest thing to deal with was the tiny size of the parts. My big ol' clumsy hands do not work so well with tiny parts. My eyesight ain't what it used to be, either (I used a magnifier for most of the work!).

    All done with assembly... time to "flame on!". I plugged in a key, a set of stereo 'fones, and my 40m dipole antenna, then plugged in the +12 VDC supply. There was a moment of silence, then ZZZZZT! C15, a 0.1 uF ceramic disc cap, went up in flames (literally... flames!). Power off. Replaced burnt-up 0.1 uF cap.

    Let's try this again. Power on. No fireworks this time, but the rig was in Transmit mode all the time. Power off. Grab the DMM. After a little probing with the Ohmmeter, I determined that either C11 or C19 was leaky. The keying circuit showed a resistance reading to ground of about 12.5K Ohms instead of the expected open circuit, and that was enough to keep the transmitter keyed. I replaced both caps (0.1 uF and 0.01 uF).

    Power on again. Now the rig was receiving. Key down... power output starts at over 1 Watt but quickly diminishes to about 600 mW with the key held down. Nothing in the transmitter feels hot. Not sure why this is happening. Will have to troubleshoot this some more. Other than the drop in TX output power, the rig seemed to be operating as advertised. It was on frequency (7.023 MHz), the sidetone worked, and I could hear signals in the passband. Listening to the rig's transmitted signal using my K3, it sounded clean, stable, and click-free. So far, so good.

    While feeling semiconductors with my finger tip looking for hot components, I discovered that the little 78L06 regulator (TO-92 package), which supplies regulated +6 VDC to the NE602, the sidetone oscillator, and the LEDs, was REALLY hot (I got a blister on that finger tip!). Grab the DMM again. The 78L06's output voltage measured only +3.78 VDC. Bad regulator IC? Crap... I don't have one in the parts bin. I do have a 7805 (TO-220 package) that I can try if I can't come up with a direct replacement. I'll have to dig around in the parts bins at work next week (I'm writing this on a Saturday).

    So... that's where I'm at with the Frog Sounds rig. Piece o' cake to assemble (once you find the missing info that ain't in the weak instructions). Was it a good value? For the price, despite requiring a little tinkering, I'd say it probably was. We'll see how it goes once I have it on the air.

    Back later with more.

    73 / 72,
    Dean K5DH
    KA0USE and KG7E like this.
  2. AA4OO

    AA4OO XML Subscriber QRZ Page

    Thanks for the write up Dean.

    The percentage of failed parts in that kit is astonishing and for those of us without much of a junk box I guess these kits would be an exercise in frustration.

    An friend who's an experienced builder recommended this fellow for a source of relatively inexpensive QRP kits...
  3. W0RIO

    W0RIO Ham Member QRZ Page

    Thanks for telling your story Dean. Seems like you got your $13 worth and not much more.
    I'd have to guess that the 78L06 is OK, but it's driving into a short. From what you said,
    it's probably another bad capacitor. With such a high failure rate, I'd replace *all* of the
    0.1uF caps. If you unsolder the output lead of the 78L06, you should be able to use
    the divide and conquer method to determine if the regulator is good/bad and whether
    the downstream circuitry is drawing too much power.

    I've "branded" my fingertips with a few TO92 and TO5 patterns in the past, ouch.
  4. G0NMY

    G0NMY Ham Member QRZ Page

    I have also just built this little QRP 40m Frog, Ok it was cheap enough. However, upon power up the Se612 that came with the kit let its smoke out! O dear! Strangely I had just picked up 10 x NE602AN off ebay as I found a few qrp circuits seem to use them.
    So I replaced the chip and all seemed fine. The tuning range on Receive isnt that great. But it does appear to work.
    My resistors came with the old school markings but I also used my multimeter just to check.
    I am now waiting for some 7.030 crystals to arrive and I will swap them over.
    I think as a beginner kit it is ok, providing you have an elmer to turn to if things go wrong.
    You may be able to get some help from your local radio club.
    The winding of the coils is slightly fiddly but do able. One thing that is different is the info I have for the coils.
    You don't mention the gauge of the wire yours used Dean, but my instructions use 0.51 Enamelled wire with 11turns on the black and 15 turns on the red toroids.
    So I agree with Dean's finding, but do not expect this little radio to perform well on crowded cw bands.
    So a great little kit to practice building and soldering but reliability of the components supplied are not great!
    I score it 3/5

    Cheers Mark GØNMY
  5. K5DH

    K5DH Ham Member QRZ Page

    Interesting... I hadn't thought about the possibility of the regulator driving a shorted part. That would certainly explain the low voltage and high temperature! I will definitely look into that before I replace the regulator. The new one hasn't arrived yet anyway. Thanks for the tip!
  6. K5DH

    K5DH Ham Member QRZ Page


    "Fiddly"... an excellent description of the act of winding toroids! As for this kit's toroids, if you search the internet you'll find two sets of toroid winding information: the "suggested" numbers of turns, and the numbers of turns that other hams found to be truly correct based on the inductance values published with the kit. I read that the "suggested" number of turns create far too much inductance. I tried those numbers and checked the inductance, found the values to be really high, and then unwound turns until I had the right value. I ended up with the same numbers of turns that the others ended up with, which are those that I wrote previously.

    I also plan to change the crystals to 7.030 MHz. I just got some in the mail the other day, but haven't installed them yet (my workbench is currently occupied by an HW-101 that I'm restoring). I don't understand why all of these Chinese kits come with 7.023 MHz crystals. Is that a QRP calling frequency in Asia? I thought 7.030 was worldwide.

    Dean K5DH
    G0NMY likes this.
  7. K5DH

    K5DH Ham Member QRZ Page

    WB0RIO, you're a genius! There was indeed a short on the +6 V regulated line! Earlier this evening, I moved the HW-101 off the bench and did some troubleshooting and discovered that C16, a 0.1 uF cap, was shorted to ground, and that was dragging down the regulator's output. Now with a full +6 Volts available, the rig's working quite well. With the short removed, the regulator is no longer scorching hot. The transmitter output is a respectable 1.2 Watts, and it no longer drops off like it did before. While I had the soldering iron heated up, I also replaced the silly 7.023 MHz crystals with a much more useful frequency of 7.030 MHz. Next step... call CQ and make a contact!

    Okay... this is a neat little kit that costs next to nothing and takes very little time to assemble. However, after having so much trouble with the ceramic disc capacitors, I'd have to recommend that the kit builder check each and every one of them with an Ohmmeter before soldering them onto the PWB. With the multi-layer PWB and its plated-through holes, it's really a bitch to replace any component. So, with all of this in mind, an even better idea might be to just toss all of the ceramic disc caps into the trash and use better quality parts! So far, all of my failed parts have been ceramic disc caps. Everything else has worked fine.

    Okay, folks... your turn! How's your Frog Sounds rig working? What problems have you encountered? Inquiring minds want to know!

    Dean K5DH
  8. G0NMY

    G0NMY Ham Member QRZ Page

    Hi Dean I must admit I didnt test it for long so I will have to check it and may rewind the coils, not difficult just time consuming to unsolder them without ruining the board. Thanks for the info. Dean maybe work you frog to frog
    who knows with 40m although the band hasnt been to hot recently. 73 Mark
  9. K5DH

    K5DH Ham Member QRZ Page

    It's Sunday evening, and after supper I headed upstairs to the hamshack to spend a little quality time with The Frog. First thing I did was to use my frequency counter to determine exactly what The Frog's transmit frequency is. The counter read 7030.6 KHz. I then fired up my K3, set VFO A to 7030.6, dialed the TX power down to 0.1 W, keyed down, and adjusted The Frog's RIT pot to give me a pleasant tone, something around 700 Hz or so. Now The Frog's TX and RX frequencies matched closely enough to reasonably expect to hear someone answering my calls. (yeah, I know, it wasn't the most scientific method in the world, but I got the desired results).

    Since the ARRL CW DX Contest was over and the band was once again available for more mundane uses, I hooked The Frog up to my 4-band parallel dipole and called CQ. On the second call, I got a response from a W4 station near Atlanta. I'm located just north of Dallas, so that's not a bad haul for 1.5 Watts and a low dipole! QSB, QRM, and QRN (from thundershowers about 100 miles away) were bad, but I copied my report, his QTH, and his name. I believe he said he was running 1 Watt, but I'm not sure (did I mention that the condx were pretty rough?). After my second transmission, I lost him to QSB. I could just about copy him, but not quite... and then... nothing. The band went away on us. Ah, well, at least I know The Frog actually works. I really enjoy 2-way QRP. Too bad Mother Nature wasn't in a good mood tonight. Another time, perhaps?

    I ordered the matching aluminum enclosure kit from a Chinese seller on eBay yesterday for about $12 ppd. That means I'll have about $35 invested in The Frog including the transceiver kit, some 7.030 MHz crystals, and the enclosure. Not bad!

    I couldn't help but notice that there's a rather loud Click! in the headphones when the rig switches from TX back to RX. Anyone else notice this? Have you done anything about it?

    I'm thinking about making the sidetone level adjustable. It's pretty stout in the headphones, especially compared to the relatively low receive audio level of a distant incoming QRP signal. Should be easy enough to accomplish; I just haven't looked into it yet.

    That's all for now. Keep them cards 'n letters comin'...
    N6ILJ likes this.
  10. K5DH

    K5DH Ham Member QRZ Page

    2016-06-27 Saturday

    I've tamed the sidetone. Increasing R10 from 1K to something greater will reduce the sidetone volume. I settled on 12K. That may be too low for some oeprators, but I really hate a loud sidetone. Try a value in the 5K range first, and go higher if you need to.

    Decreasing CP10 from 1 uF to something less will speed up receiver recovery time. I settled on 0.33 uF. TX/RX turnaround is now much faster than before. It isn't QSK, but it's not bad.

    I did some more research on the clicking sound. It isn't happening when the rig switches from TX back to RX. It happens on the leading edge of the first two dits or dahs, then it doesn't happen any more until there's a pause in the keying train. Using the DMM, I discovered some strange behavior in the audio amp stage (or at least it's strange to me). I made some DC voltage measurements and recorded the values. For all of these measurements, I used a straight key. I keyed-down and held it for about 15 seconds, then went key-up again. Refer to the schematic below. I need some help understanding the measurements.

    Point A -- RX: +12 (why is this so high?)
    TX: 0-ish (as expected, since this line is grounded by the key)

    Point B -- RX: +7.3, TX: jumps right to +12.8 and decreases to +7.7 in about 5 seconds.
    This is coming off Pin 5 (Vout) of the LM386.

    Point C -- RX: +7.2, TX: drops to 0.5 on key-down, but on key-up going back to RX
    it climbs back to +7.2 in about 5 seconds

    Point D -- RX: 3.0, TX: holds at just under 3.0 while key-down, but on key-up going back to RX
    the voltage drops immediately to near 0 and climbs back to 3.0 in about 5 seconds

    Is this behavior somehow related to CP5 and CP9 charging and discharging? What's causing the voltage at the output of the LM386 to jump to +12.8 when the rig goes into TX mode? As you can tell, I'm not a "solid state guru". I mainly work on tube-type gear!

    Your help will be appreciated!

Share This Page