Hello all.

I've just received my new BITx20 transceiver via IndiaPost.
It arrived quicker than predicted and the 'kit' is very nicely assembled.
Checked it mechanically and all is well, toroids all connected.

Reading the notes the designer mentions 'better than 0.1uV sensitivity.'
Having lashed it together on the bench it seemed a bit deaf, I checked everything was connected as per the instructions, but still the same.
Compared sensitivity with my Yaesu and that was much more sensitive.
So out with the Marconi signal generator, the Yaesu sensitivity is about 1uV and a reasonable tone heard. The BITX20 was more like 100uV to get a reasonable tone heard.
That was at 7MHz but it's the same at other frequencies.

I'm happy to do some research, but thought I had better see if anybody out there has had a low sensitivity unit?

Thanks for any assistance,

BobM0RHE

--
Bob Head, Rotronics Systems Limited, 01252 722686

Bob,
What radio do you actually have?? This list covers the entire BITX family.? The name is a hold over from Farhan's first BITX, the 20.? You referred to a BITX20 kit delivered via India post so I am assuming you bought it from HFsignals.com.? If that is correct, they currently sell two transceivers neither of which is the BITX20.? The BITX40 that covers the 40m band and the ?BITX that is a multi band radio.? There are also BITX20 kits in the wild so I may be off base in my assumptions.? Either way, once we know what you have we can be of more help.
--

开云体育

Hi Doug

Sorry, making assumptions here.
It's the uBITX multiband radio.

I did get this a few weeks ago from HFsignals.com.
Bob

Bob,
What radio do you actually have?? This list covers the entire BITX family.? The name is a hold over from Farhan's first BITX, the 20.? You referred to a BITX20 kit delivered via India post so I am assuming you bought it from HFsignals.com.? If that is correct, they currently sell two transceivers neither of which is the BITX20.? The BITX40 that covers the 40m band and the ?BITX that is a multi band radio.? There are also BITX20 kits in the wild so I may be off base in my assumptions.? Either way, once we know what you have we can be of more help.
--

-- 
Bob Head, Rotronics Systems Limited, 01252 722686

Bob

There should not be a huge difference in sensitivity.? possibly your bfo setting is out of calibration.? how do ssb signals sound?? make sure you don't have a short across the antenna connection in your wiring, or have the connections reversed as I did at first.

The ubitx has a bit less overall gain than many commercial rigs, but little or no difference in sensitivity. Another test, using headphones, when you attach a good antenna the noise should go up, on the lower bands especially.

Curt

开云体育

Hi Curt

Thanks for the reply.

I did think about the wiring of the antenna connector when I was cabling it to the co-ax for the signal generator, it's easy to swap that around.
UBITx has a claimed sensitivity of 0.1uV, (Page 4 - a 0.1uV signal is clearly audible)

The injection oscillator might be out of calibration, but this is brand new out of box, before I install it into the case I have in mind (an ex-army radio) I wanted to check it worked correctly. The BFO being out would alter the tone heard in the headphones. The signal generator is AM.

It is possible that the headphones I use are to low an impedance, I'll try a speaker amplifier tonight and see if I can hear down to 0.1uV. 100uV from the calibrated Marconi is nicely audible on the UBITX but it is a bit deaf on my long -wire.
I'll report back!

Regards

BobM0RHE

Bob

There should not be a huge difference in sensitivity.? possibly your bfo setting is out of calibration.? how do ssb signals sound?? make sure you don't have a short across the antenna connection in your wiring, or have the connections reversed as I did at first.

The ubitx has a bit less overall gain than many commercial rigs, but little or no difference in sensitivity. Another test, using headphones, when you attach a good antenna the noise should go up, on the lower bands especially.

Curt

-- 
Bob Head, Rotronics Systems Limited, 01252 722686

Hi Bob, as Curt already said, the uBitx per se is as sensitive as any other rigs. As many parts of the RX circuits are shared with the TX, if you can a reasonable output power, then you can exclude a large part of the RX chain might have an issue.

Bob

The 12 MHz crystal filter is quite narrow. If the bfo is way off,? the signal will be highly attenuated by the shape of this filter. Second,? the receiver has less total gsin than some receivers so a good antenna is needed, not just a short piece of wire. My bfo came way off and it wasn't easy to get it aligned. When aligned, big signals will be quite loud in headphones needing the volume control to be set quite low. Weak signals might need near full volume. If you like to use a speaker, you may wish to use an amplified one, there are many inexpensive ones out there. But first important to align the bfo.

Curt

开云体育

Hi Curt

You were bang on with this.
I put a DFM onto R110 which is the BFO oscillator and it was 5KHz off the 12MHz

The calibration option when selected offers adjustment, tweaking away improved the sensitivity to more like the 1uV promised.
I'll read the frequency it needs to be set to to give the sensitivity at some stage and do some calculations, I expect that will give me the exact crystal filter response.
The cheapy encoder supplied is not brillant and tuning does jump about. I have a nice Bournes part rescued from a junk sale unit and that improves the tuning nicely, it's 128 step which is far to many steps, but I'll look around for a part with less steps. It's not a concern as that's not my intended use for the BITX.

One calibration option if you are not careful puts the board into transmit which upset the RF signal generator, I did not have 12v on the PA stage so no damage done, but I need to spend some more time reading up on this.

Thanks very much for your advice, I'll settle down and do some more testing before I build the board into it's case.

****

Not sure how interested anybody is in this,
Short history;

I bought a couple of solid state (1980's) HF transceivers from a 4x4 vehicle rally. With PA and Antenna auto tuners. ( I like 'green boxes'!)


It was made in the UK but only sold into Australia as far as I can tell.
The design made extensive use of tantalum capacitors which if they get moisture in can catch fire (I've seen a tiny flame coming out of one)
The internals of the radio, mainly the flat flexi wiring it made extensive use of, were so badly damaged I made a decision to replace the electronics, and the BITX is just perfect size to fit into the existing case, with some room for a controller and antenna filtering / tuning.

I bought the BITX? with the intention of writing code to control the Si part and allow me to use the control panel from the Army Radio which is basically about 20 switches to programme frequencies in, and end up with a working Raven radio.

Again, many thanks for your help,

BobM0RHE

Bob

The 12 MHz crystal filter is quite narrow. If the bfo is way off,? the signal will be highly attenuated by the shape of this filter. Second,? the receiver has less total gsin than some receivers so a good antenna is needed, not just a short piece of wire. My bfo came way off and it wasn't easy to get it aligned. When aligned, big signals will be quite loud in headphones needing the volume control to be set quite low. Weak signals might need near full volume. If you like to use a speaker, you may wish to use an amplified one, there are many inexpensive ones out there. But first important to align the bfo.

Curt

-- 
Bob Head, Rotronics Systems Limited, 01252 722686