Topics

Low Receive Audio

Terence Taylor
 

Just finished wiring up my V.4 kit from Farhan. I have the EXTREMELY low receive issue. I have rated power output on transmit and very loud CW sidetone audio. What RX audio that I can hear (from a local broadcast station) is quite clear and understandable. Anyone have any thoughts/guidance?

I have tried the calibration and BFO setting and neither one seems to do any good. I have loaded the CEC firmware, but this was present before that.

Jerry Gaffke
 

I assume you are checking for power out in CW mode.
Does the transmitter work in SSB mode?
That would prove out the modulator/demodulator, the 12mhz crystal fllter, and the 45mhz crystal filter.
None of those are involved when transmitting CW.



On Tue, Aug 7, 2018 at 07:57 PM, Terence Taylor wrote:
Just finished wiring up my V.4 kit from Farhan. I have the EXTREMELY low receive issue. I have rated power output on transmit and very loud CW sidetone audio. What RX audio that I can hear (from a local broadcast station) is quite clear and understandable. Anyone have any thoughts/guidance?

I have tried the calibration and BFO setting and neither one seems to do any good. I have loaded the CEC firmware, but this was present before that.

Terence Taylor
 

Both CW and SSB are making rated power.

Jerry Gaffke
 

OK, so transmit works well on both CW and SSB.
I assume that's transmitting into a dummy load.

What kind of antenna do you have?
These are made to work with a good efficient and resonant antenna system, suitable for transmitting.
Ten feet of wire hanging out the window is not going to cut it.
The typical shortwave broadcast receiver has a lot more RF gain so it can deal with crummy antennas,
if the uBitx had that much gain it would overload when used with a decent ham antenna.

You might try touching your antenna coax center conductor to T2 pin 1, coax braid to the groundplane
on the bottom of the rig.   This goes around the relays at K1 and K3,
also around the 30mhz lowpass filter at L1,2,3.  Does it get louder?

Also short across the relay contacts labeled M1 and M2.
Those are there just to reduce the kerchunk sound when you hit the PTT switch to transmit.
A bad relay contact would seriously reduce receive audio (probably to nothing at all).

Otherwise it's down to the RF amps at Q10 and Q30, also the audio pre-amp at Q70.
Those are all auto-stuffed surface mount parts, and we seldom hear of trouble with any of that.
But it's possible.
Get some good light and a magnifier of some sort, look for bad solder joints.

What kind of test equipment do you have?

Jerry



On Tue, Aug 7, 2018 at 08:23 PM, Terence Taylor wrote:
Both CW and SSB are making rated power.

ajparent1/kb1gmx
 

First and foremost...

Make sure the BFO is correctly set.  Many find it works better after that.
Then make sure the audio amp is working correctly!  The audio amp has had issues.

Do that is before going deeper and more obscure.

Allison

Terence Taylor
 

Jerry
Antennas - MA5B, Gap Challenger. I own LOTS of test equipment including a 200M scope,  DC-1G spectrum analyzer and a Wavetek 5100S service monitor with SSB generate and receive.

Alison, BFO alignment attempt made no difference and I have been busy today with work issues. Hope to get back to it layer this evening.

Jerry Gaffke
 

If SSB transmissions give sufficient power and sound good in some other receiver,
then that checks out much of the uBitx receiver as well.
Sounds to me like you are down to those parts enumerated in my previous post.

And sounds like you have more gear than most to look at it with.

Jerry



On Wed, Aug 8, 2018 at 02:00 PM, Terence Taylor wrote:
Alison, BFO alignment attempt made no difference and I have been busy today with work issues. Hope to get back to it layer this evening.

Jerry Gaffke
 

As has been mentioned elsewhere, the coax connector provided with the kit is not always machined to spec.
Specifically, the center pin of your antenna coax connector may not make contact.
So should also try wiggling the antenna coax while receiving.



On Wed, Aug 8, 2018 at 02:00 PM, Terence Taylor wrote:
Jerry
Antennas - MA5B, Gap Challenger. I own LOTS of test equipment including a 200M scope,  DC-1G spectrum analyzer and a Wavetek 5100S service monitor with SSB generate and receive.

Alison, BFO alignment attempt made no difference and I have been busy today with work issues. Hope to get back to it layer this evening.

ajparent1/kb1gmx
 

I finally looked at my connector...

Its machined correctly...  for a connector designed for 75 ohm use.

The 75 ohm parts, plug and matching connectors are very similar
on face but  if you mix them you get poor connections or the larger
damages the smaller.  The female 75 ohm suffers more as the
50ohm pin is larger and speads it.

Its just one of those things that they don't teach in school but
us old farts just know because it bit us once!

The 75 ohm version was more common to video systems and
some network stuff. 

The other one that bits people Teflon "RG-316"cable deals
that turn out to be RG179 75 ohm cable (handy too!).  They
look the same but they are not (Smaller center conductor).

Yes, I threw it out.

Allison

ajparent1/kb1gmx
 

Mis-wired audio pot?  Open audio pot, had one with no functional connection
to the end of the element (looked but didn't ohm out). 
Hint touch the wiper of the pot with it turned all the way up hear click or hum?

Crimped connector that wasn't stripped (factory).  Got a  new RL02 disk
that way as everyone replaced everything save for the base AC harness.

Make sure Q70 is about 1/2 the supply?  if not it may be bias, solder, or bad?

make sure there is a path through K3 pins 14 and 12 per schematic.

Q74 could be shorted (solder) or just bad.

Bad device in the audio amp.  Is the junction of Q72 emitter at or near 1/2 the power supply voltage?
I not read postings on fixing he amp.

Also ubitx.net has a lot of the problem/fixes.

Allison

Jerry Gaffke
 

Allison,

You have plenty of experience with BNC's, more than I.
But check out this post:
    https://groups.io/g/BITX20/message/39196

In particular:
"Wikipedia has this to say:     https://en.wikipedia.org/wiki/BNC_connector\

"The different versions are designed to mate with each other,[2] and a 75 ohm and a 50 ohm BNC connector which both comply with the 2007 IEC standard, IEC 60169-8,[9]will mate non-destructively. At least one manufacturer[10] claims very high reliability for the connectors' compatibility."

Now that is only "one manufacturer", there may be trouble with others, I don't know.
My uBitx BNC was flaky, but judging from descriptions on the web as pointed to in that post,
mine was constructed as a 50 ohm BNC.

Jerry 


On Wed, Aug 8, 2018 at 03:25 PM, ajparent1/KB1GMX wrote:
I finally looked at my connector...

Its machined correctly...  for a connector designed for 75 ohm use.

The 75 ohm parts, plug and matching connectors are very similar
on face but  if you mix them you get poor connections or the larger
damages the smaller.  The female 75 ohm suffers more as the
50ohm pin is larger and speads it.

Its just one of those things that they don't teach in school but
us old farts just know because it bit us once!

The 75 ohm version was more common to video systems and
some network stuff. 

The other one that bits people Teflon "RG-316"cable deals
that turn out to be RG179 75 ohm cable (handy too!).  They
look the same but they are not (Smaller center conductor).

Yes, I threw it out.

Allison

Jerry Gaffke
 

He says sidetone is plenty loud but receive audio very weak.
The sidetone comes in before the volume pot.
Though worth checking that the volume pot varies the sidetone volume as expected.


Given that and the fact that the transmitter works in SSB mode,
it's sounding like one of the two IF RX amps or the audio preamp.   
All just autostuffed surface mount parts, no hand work.
Or possibly the M1/M2 relay contacts.

Jerry



On Wed, Aug 8, 2018 at 03:36 PM, ajparent1/KB1GMX wrote:
Mis-wired audio pot?  Open audio pot, had one with no functional connection
to the end of the element (looked but didn't ohm out). 
Hint touch the wiper of the pot with it turned all the way up hear click or hum?

Crimped connector that wasn't stripped (factory).  Got a  new RL02 disk
that way as everyone replaced everything save for the base AC harness.

Make sure Q70 is about 1/2 the supply?  if not it may be bias, solder, or bad?

make sure there is a path through K3 pins 14 and 12 per schematic.

Q74 could be shorted (solder) or just bad.

Bad device in the audio amp.  Is the junction of Q72 emitter at or near 1/2 the power supply voltage?
I not read postings on fixing he amp.

Also ubitx.net has a lot of the problem/fixes.

Allison

Ralph Mowery
 

I was thinking it is the N connectors had the center pin problem.  The BNC are the same size but the insulating material is made different so the  impedance would be 75 instead of 50.  If that is the case, that bump is so small it would not make any difference in the Bitx.



On Wed, Aug 8, 2018 at 6:25 PM, ajparent1/KB1GMX <kb1gmx@...> wrote:
I finally looked at my connector...

Its machined correctly...  for a connector designed for 75 ohm use.

The 75 ohm parts, plug and matching connectors are very similar
on face but  if you mix them you get poor connections or the larger
damages the smaller.  The female 75 ohm suffers more as the
50ohm pin is larger and speads it.

Its just one of those things that they don't teach in school but
us old farts just know because it bit us once!

The 75 ohm version was more common to video systems and
some network stuff. 

The other one that bits people Teflon "RG-316"cable deals
that turn out to be RG179 75 ohm cable (handy too!).  They
look the same but they are not (Smaller center conductor).

Yes, I threw it out.

Allison