Monthly Archives: June 2014

RF boards here

Hello,

The RF boards have finally arrived, i have updated the Order page. Apologies for infrequent stock, but i was doing some improvements and that is why i got only small batches. Now i believe both boards are finalized, i can order bit more and it will be possible to order both boards the same time and save on postage.

Chris

Some PCBs and LCDs available

I have been contacted by many fellow hams for boards and LCDs, but it was hard to keep track of requests, apologies for that. I have updated the Order page with new type of shopping cart. Please let me know if there is a problem using it.

New amp and mods

I have spent the last few days improving a BJ300 CB amp, to be useful for some mcHF QRO testing. I could have bought a proper, expensive amp, but i don’t have the time to make contacts unfortunately, so it would not be a wise investment. Also i have managed to learn a thing or two.

Bo57n0bIMAAvojX

This is the amp on the inside, it is well made, but so many design decisions make it not fit for the HF ham bands. First thing that springs to mind – it is class C, clearly visible from the schematics as well:

Bo572opIgAABA6bConnecting it to a dummy load with a tap shows how unclear the signal is:

Bo58vG2IcAAE9FcSo, there is a need for a bias and external LPF. First thing, how to add bias. Checking the schematics and PCB, it is clear the bias is best fed to the center of the secondary on the input transformer(T2), unfortunately this is implemented as two copper pipes inside a binocular core, soldered with lots of crappy solder on the dual PCB with lots of vias and huge ground plane

Bo59CK9IQAAYuFNNo worry though, i have a secret weapon, it is called ERSA and is a marvel of the German engineeringBnRrJx3IcAA8r27The transformer was not match for this miniature soldering iron! And here the modified version, with the centre insulated

Bo591hsIYAABAb9As for the bias schematics, i used the ready idea from this amp bigger brother, called KL400. The only change was using LM2941 for 4.9V stabilized power supply, and its inhibit pin to the collector TR2, so the bias current is supplied only when keying down.

Bo5_yksIcAAbgvVAnother useful add on would be ACC line from the mcHF controlling PTT, instead of current RF sensing, that is not very good idea for SSB operation.

Bo6APA8IgAAat9DA small 40m LPF was in order too, with whatever parts i had. It should survive few tests, i believe, and it looks good on the analyzer

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Soon, on the bands…