Experience with Amazon kit and troubleshooting

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N4XTL
 

Posts: 24
Joined: 08 Jul 2022, 01:44

Experience with Amazon kit and troubleshooting

Post by N4XTL »

Hi,

I ordered my kit from Amazon (seller Malahit) and assembled it this week. There were no major issues with assembly and everything went pretty smooth. Mine came with the bootloader installed, so updating the firmware with my callsign was easy.

Upon testing power output and efficiency, the only band that checked out good was 80m, and only at the very bottom. All bands had highest output at the bottom in the CW portion, with power output dropping to as little as 2.5 watts toward the top of some bands. I tried tweaking the series inductors in each filter section but of course did not have enough range of adjustment just by fiddling with turn spacing. The tuning videos suggest that removing turns is the only option in that case, so I removed a turn each from L11 and L31 to try and improve 20m and 40m.

This did indeed help. 20m is nearly spot on now. 40m is still low. Transmitting below the band edge (into a dummy load of course) I found power output and efficiency to be 5.2W and 85% at about 6.9 MHz. So I guess I will remove another turn from L31...

I guess my question is, should I continue with this approach? Keep removing turns from the series inductor in each filter section until I center the passband where I want it? At what point do I need to consider the other inductors in the filter sections, or L15?

I will say that I know I wound the correct number of turns from the instructions for each inductor. Something in the kit must be off that caused all of the inductors to end up too high in value. The toroids perhaps? Has anyone else experienced this with their kits?

I will also say that, even in it's current state, my radio works! Tonight from North Carolina in the US, I contacted a 13 Colonies station in New York on 40m and a POTA park in Missouri on 20m, using the onboard mic. Both heard me without issue. Amazing!

Thanks

Dan Watson
N4XTL
John
 

Posts: 49
Joined: 19 Feb 2022, 08:56

Re: Experience with Amazon kit and troubleshooting

Post by John »

Fun little rigs, aren't they? And amazing performance for the size and money. Firmware definitely rules.

Cores inductance and losses do vary, perhaps by as much as 5 or 10%, not only from different suppliers, but even between batches from the same supplier.

{"40m is still low. Transmitting below the band edge (into a dummy load of course) I found power output and efficiency to be 5.2W and 85% at about 6.9 MHz. So I guess I will remove another turn from L31..."}

So what do you mean by "too low?" You mention neither the power nor the efficiency in the band itself, neither at the bottom nor top of the band.

Based on my experience the rig's output always drops as you tune from the bottom of any given band to the top, the wider bands of course dropping more than the narrow bands. I think the idea is to decide what parts of the band you want to optimize and adjust for that range. I've made it a rule with my rig not to exceed 6 W output at the very bottom of any band, (I'm an Extra, so there is a small chance I will want or need to go down that low on certain bands at some point,) then I just live with what I get at the top. Anything close to 3 Watts works for me. Expensive rigs use lower efficiency push-pull broadband amps with feedback controls to keep the RF output constant. These simple Class E amps will always drop in output as the frequency increases and the FET's gate capacitance has to be charged and discharged ever quicker. I'm actually more concerned with getting the highest efficiency than the highest power, as the rig is being set up to run on battery power in the field, and as an emergency back-up rig during extended power outages.
N6ALT
 

Posts: 21
Joined: 02 Jan 2022, 20:02

Re: Experience with Amazon kit and troubleshooting

Post by N6ALT »

I bought one from the same seller on Amazon, (Sunny's store), and ran into the exact same results. I'm getting about 5 watts at the bottom of all the bands and about 2.5 to 3 watts at the top of the bands, spreading the turns around didn't accomplish much so I'm going to just live with it as I already hot glued my toroids down to the board :|

Joel
N6ALT
N4XTL
 

Posts: 24
Joined: 08 Jul 2022, 01:44

Re: Experience with Amazon kit and troubleshooting

Post by N4XTL »

I have finished tuning my radio and am pretty happy with all of the bands now. I ended up taking a turn or two off of nearly every inductor in the filter sections. The 2nd harmonic notches were verified for all bands on a NanoVNA and are spot on after adjustments.

80m
L51 - Remove 1 turn
L52 - Remove 1 turn
3.510 MHz - 7.09W / 65% efficiency
3.750 MHz - 5.42W / 79.7% efficiency
3.990 MHz - 3.3W / 75% efficiency

60m
L41 - Remove 1 turn
L42 - Remove 1 turn
5.332 MHz - 6.1W / 82.4% efficiency
5.405 MHz - 5.4W / 82.1% efficiency

40m
L31 - Remove 2 turns
L32 - Remove 1 turn
7.010 MHz - 5.49W / 79.9% efficiency
7.150 MHz - 4.57W / 79.0% efficiency
7.290 MHz - 3.84W / 78.6% efficiency

30m
No adjustments to L21 and L22
10.110 MHz - 4.68W / 78% efficiency
10.140 MHz - 4.57W / 77.8% efficiency

20m
L11 - Remove 1 turn
L12 - Remove 1 turn, compress remaining turns substantially
14.010 MHz - 5.12W / 79.1% efficiency
14.150 MHz - 4.69W / 78.5% efficiency
14.340 MHz - 4.15W / 78% efficiency

I tuned the 80m section toward the SSB portion of the band and will not use it at the low end. At exactly 3.573 MHz the power hits 7.69W, so some FT8 would very likely blow the FETs. The measurement I gave for the upper end looks quite bad, but actually around 3.85 - 3.9 MHz where I would normally pick a frequency, power is around 4.5W with 79% efficiency. Very usable.

The value of L12 in the 20m section was kind of right in between turns, and I couldn't space them far enough apart with the normal 7 turns to get what I needed. I was able to improve the position of the 2nd harmonic notch by removing a turn and compressing the remaining turns as far as they would go.

It's possible that I could improve the 30m section by removing a turn from L21 and compressing the rest. It's so close to spot on though, I decided to leave it.

Efficiency across the board is a bit low. Perhaps I will experiment with removing a turn or two from L15.

I am likely going to order a second kit from Amazon and build a second radio with my new values here, just to see if the results are repeatable.
N4XTL
 

Posts: 24
Joined: 08 Jul 2022, 01:44

Re: Experience with Amazon kit and troubleshooting

Post by N4XTL »

N6ALT wrote: 08 Jul 2022, 14:25 I bought one from the same seller on Amazon, (Sunny's store), and ran into the exact same results. I'm getting about 5 watts at the bottom of all the bands and about 2.5 to 3 watts at the top of the bands, spreading the turns around didn't accomplish much so I'm going to just live with it as I already hot glued my toroids down to the board :|
Thanks for confirming that I'm not entirely crazy or can't count. :D
N6WLM
 

Posts: 20
Joined: 12 Jul 2022, 03:15

Re: Experience with Amazon kit and troubleshooting

Post by N6WLM »

I had the same issue with my Amazon kit. I had to take winding off every toroid also. The T37-2 toroids I received are red/red not red/clear as I've seen in most kits. Could they be the wrong type?
N4XTL
 

Posts: 24
Joined: 08 Jul 2022, 01:44

Re: Experience with Amazon kit and troubleshooting

Post by N4XTL »

I ordered and assembled a second Amazon kit. I used the adjusted number of turns for inductors that I posted above with good results. I had to fiddle with the spacing of the turns quite a bit to tune the filters, but in all cases I had the right number of turns wound. So there was consistency there at least.

Power is quite good on this radio, but efficiency is lower, around 70% for all bands. Additionally, my 2nd harmonic notches are not as deep as my first radio. The notches were about -65 dB on the first radio, but only -50 dB on this second radio.

So I have some work to do on this unit to try and improve it. It is clear to see the difference in efficiency between the two units just by looking at current during transmit from the bench power supply. This new second radio is over 100 mA higher during transmit.

It's interesting that there is so much variation in these kits, even when ordered from the same vendor at nearly the same time. I am very close to ordering a blank RF board PCB and sourcing the capacitors myself to see how good I can make one.
KO4TCY
 

Posts: 13
Joined: 07 Aug 2022, 23:42

Re: Experience with Amazon kit and troubleshooting

Post by KO4TCY »

Hello, I also ordered a kit from Amazon and found the need to remove turns from the LX2 cores. Did you have any issuees with the SWR measurement with your kits?
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