The Ubitx Thread

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Buick Mackane
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The Ubitx Thread

Post by Buick Mackane »

I have a few other threads regarding my modifications to this transceiver but thought i'd consolidate them all here. First up these mods are really only applicable to early versions, My radio is version V4.3, When first built the radio wasn't fit for purpose, So here is a list of the issues with it and the mods i carried out to turn it into a usable transceiver,

The radio doesn't have any AGC, So when receiving a strong signal your ears get blown clean off, I got round this by building a small circuit that uses an LDR (Light dependant resistor) The incoming audio is rectified and used to power an LED, The LED Shines onto the LDR lowering the resistance which in turn lowers the resistance across the volume potentiometer lowering the volume. The stronger the signal the brighter the LED shines, Details of the circuit and schematics are available online.

Next thing was to swap out the bandpass relays for better quality ones, Harmonics can leak across the stock relays causing harmonics to be transmitted, I used Axicom Relays., I Still need to swap out a few inductors to reduce spurs.

When first built the radio has virtually no RX Audio, I added an LM386 Audio amp but even that wasn't enough to boost the volume, I had to build a small preamp ahead of the LM386 To get the volume up to a decent level, After boosting the volume i then got blasted with feedback on TX Which i got round by adding a relay to take the speaker out of circuit during TX..The radio was designed to be listened to in a quiet room with headphones at full volume, No idea why.

The TX Audio wasn't much better, You have to go into the menu and adjust the BFO To around 11.996.6Khz As standard it's set to 11.995.0 Khz Which results in very thin and tinny audio and isn't enough to drive the radio on SSB, Even after adjustment i still wasn't getting enough drive to be heard so i homebrewed an amplified mic, Now i get plenty of audio. Output power is around 10 watts on the lower HF Bands and falls off as you go higher in frequency to around 2 - 3 watts on 10m.

So with about a fiver spent on parts and a bit of time invested in it i now have a usable HF Rig that in total cost me around £100, Which these days is the price of a NOS Fidelity 1000 :)

That's about it, Hope the above info is useful to somebody who has an early version of this radio, There's plenty more information available online. Any questions just ask :) Or share your experiences of this radio, Modifications you've carried out, Pics etc.

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DX-Digger
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Re: The Ubitx Thread

Post by DX-Digger »

Is the AGC design by Peter VK3YE I know he came up with that kind of a system, its something I never would how imagined.
Do you get enjoyment out of building little rigs and getting them on the air?
Thats the fun part for me being honest, I really should use them more on air but never seem to bother with them lol
I like your case design looks good.
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Re: The Ubitx Thread

Post by Buick Mackane »

DX-Digger wrote: 02 Nov 2022, 01:42 Is the AGC design by Peter VK3YE I know he came up with that kind of a system, its something I never would how imagined.
Do you get enjoyment out of building little rigs and getting them on the air?
Thats the fun part for me being honest, I really should use them more on air but never seem to bother with them lol
I like your case design looks good.
Yeah it's his design. Ingenious but simple, It can be defeated by really strong stations with really loud audio by works ok for the most part, I Get enjoyment out of electronics in general pal could solder all day long :)
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Re: The Ubitx Thread

Post by Buick Mackane »

I Would definitely recommend this mic preamp circuit, It makes the difference between being heard and not being heard, You can use any general purpose NPN Transistor, 2N2222 - 2N3904 ETC. Runs off the radios own supply so no battery or external power supply needed


Small enough to fit inside your mic
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Re: The Ubitx Thread

Post by Buick Mackane »

Been experimenting with the LDR AGC circuit, If you swap out the silicon rectifying diode and replace it with a germanium one you get a lot more drive which pulls the volume farther down, It can cope with EA3JE Now :) He must be the loudest station in europe
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Re: The Ubitx Thread

Post by Auldgeek »

There's a few AGC designs that will work very well.
My Ubitx uses an AGC design from ND6T. I find it works very well with no overshoot. It was originally designed for the Bitx40, but can be modified to suit the ubitx.
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Re: The Ubitx Thread

Post by Buick Mackane »

Auldgeek wrote: 08 Nov 2022, 11:39 There's a few AGC designs that will work very well.
My Ubitx uses an AGC design from ND6T. I find it works very well with no overshoot. It was originally designed for the Bitx40, but can be modified to suit the ubitx.
Seen that design whilst trawling google, I got fed up with the LED-LDR System, It worked ok to an extent, But there was a slight delay before it kicked in and a loud crunch when it did kick in..So i came across this circuit online and so far so good, You'd almost swear when listening to it that the radio had proper AGC, Although theres no real substitute for real AGC That reduces front end gain..


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Re: The Ubitx Thread

Post by Buick Mackane »

The above circuit needs two audio amps, One to drive the levelling circuit then one to drive your speaker, I had a spare amp module doing nothing so i used that as the driver, The speaker amp is an LM386 Module.





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Re: The Ubitx Thread

Post by Buick Mackane »

Been experimenting with some mics, Have a cheap altai noise cancelling mic with two dynamic elements, But there wasn't enough drive so i've installed a condenser mic element and tomorrow i'll built a small amp for it,

Also have an altai DMC-510 Power mic but it still had insufficient drive so i swapped the dynamic element for a condenser and now have plenty of drive but not tried it on air yet.
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