Possible bad trace on RF board?

Post Reply
K0BRK
 

Posts: 4
Joined: 22 Feb 2023, 13:04

Possible bad trace on RF board?

Post by K0BRK »

Any help appreciated. I purchased the Malahit kit from Amazon and put it together. I powered it up on 5v through the usb connection. I can go through all of the menu options, switch bands, modes, etc. For some reason I am not receiving any signal, not even noise although the display shows S4 noise level. When transmitting CW into a dummy load, the display shows 0.0W and 0.00% efficiency (I’m not in practice mode). While doing some troubleshooting, I removed T1 and found two pads for the T1 that I believe should have continuity but don’t seem to. They are the top two adjacent pads on the trace schematic for T1. (sorry, no pictures. I can’t seem to get them sized correctly)

Do you think this might cause the problems that I am having?

Thanks!
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: Possible bad trace on RF board?

Post by dl6sez »

Hello OM,

you bought a Malahit are you sure you are here in the right forum ;)
If you bought a (tr)uSDX not an uSDX nor another different type of Kit than you are maybe right here.
If i have understood your question, i can not conclude which solder points you are talking about...
So take a good quality photo mark where your problem seems to be and send it to us here please.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
K0BRK
 

Posts: 4
Joined: 22 Feb 2023, 13:04

Re: Possible bad trace on RF board?

Post by K0BRK »

Thanks for responding to my question. I bought the kit from the Amazon link provided on DL2MAN’s website. I understood that those suppliers were legitimate. I hope so anyway! I rewound the T1 and now I have power and :shock: efficiency readings, but they seem quit low. I am currently powering up with USB 5v.

80m 0.67W and 74%
60m 0.32W and 64%
40m 0.30W and 60%
30m 0.42W and 60%
20m 0.40W and 66%

I’m attaching a pic of the pads I was referring to in my post. I’m not showing continuity on the multimeter.
Attachments
29B4FE18-242F-4322-8F5B-0E6C0A3B12E1.jpeg
29B4FE18-242F-4322-8F5B-0E6C0A3B12E1.jpeg (194.78 KiB) Viewed 973 times
s57l
 

Posts: 56
Joined: 30 Dec 2021, 21:30

Re: Possible bad trace on RF board?

Post by s57l »

Well, powering from usb should roughly give you 0,5w.
So, you are quite close to what it should be.
Needs some toroids tweaking.
Do you have reception now?
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: Possible bad trace on RF board?

Post by dl6sez »

Hello OM,

as the OM from Slovenia said... you can try now quickly with 12V but than adjust your second harmonic notch, eg. see video of DL2MAN on youtube, with NanoVNA or other Network Analyser (also a scalar one is good enough for this) and than tweak your remaining toroids for maximum power on the bands.
...and at T1 output side to Antenna one could measure a short circuit when T2 is already mounted not where you measured.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
K0BRK
 

Posts: 4
Joined: 22 Feb 2023, 13:04

Re: Possible bad trace on RF board?

Post by K0BRK »

Thanks for the replies! I will proceed as you both have suggested.

I still do not have reception. I’m assuming I should at least be receiving noise over the speaker. I believe the speaker is working but need to verify by trying headphones. Any ideas on what to look at for the reception issue?

Thank you
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: Possible bad trace on RF board?

Post by dl6sez »

Hello OM,

try the receiver without the second PCB (RF-PA and LPF not necessary for RX test).
Contact RF Pin on connector J3, the interconnection between the boards.
You can simply use a few meters of whire there and should be able to hear a few stations on the bands, for sure depending on day or night time :)
If than nothing is heard... than you have to check, starting from Q1 through all components up to Atmega328 inputs of IQ signals.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
K0BRK
 

Posts: 4
Joined: 22 Feb 2023, 13:04

Re: Possible bad trace on RF board?

Post by K0BRK »

Greetings again,

Thanks for all of your help. I got the rig running and checked the second harmonic on all bands. They all seemed to be perfect except 60 meters and the notch was way short of the second harmonic frequency. I tried making adjustments but couldn’t even get close. Maybe need to add or subtract a turn on L42??

Anyway, I hooked the radio up to my off center fed dipole and made a contact on 20 meters with another guy that was also operating QRP! He was using a different radio, but said that he also has a (tr)uSDX that he had built (he was in Chicago). What a small world!

Thanks again,
73’s
Brooke
dl6sez
 

Posts: 399
Joined: 30 Dec 2021, 22:54

Re: Possible bad trace on RF board?

Post by dl6sez »

Hello OM Brooke,

nice to hear your (tr)uSDX works now :)
Yes you can add or substract a turn on L42. Substract one if it is short below harmonic qrg.
You can also leave it as it is if it isn't too far from the point and the output power is ok.
60m harmonic is maybe due to the fact that it is tuned for Europe a little bit out of tune at harmonic in USA.
Don't know your band at 60m.

73 de Chris
Chris DL6SEZ, JN48XL near Ulm, Southern Germany
Post Reply

Users browsing this forum: No registered users and 2 guests