Topics

Rx Radio #ubitx-help

sridhar
 

I had ubitx ,currently using for RX Only ,its my first HF set ,Ubitx having 3 Mhz to  30 Mhz Frequency ,
1)Can i use this for Normal Radio RX i.e SW , i am able here radio but audio is not able to recognize. 
2)  what changes do need to do in this set to added any component to get full audio from SW frequency 



de 
vu3pen
sridhar 

Mike aka KC2WVB <rb5363@...>
 

OK, Sure you can listen to what you refer to as normal Shortwave because the radio's reciever covers the entire High Frequency spectrum. You will need an antenna system that allows you to tune the section of the spectrum your interested in listening to and adjust its tuning as you slide up or down the band. A 58 foot piece of wire that runs vertically for 17 feet before it bends at a right angle for the rest of its length coupled to a inexpensive MFJ 1600 long wire tuner works extremely well when the tuner and reciever are grounded to something like a cold water pipe.

The AM stations will sound a bit weird at first because if your not right on their carrier frequency the difference is heard as a high pitched tone that progressively becomes lower and goes to zero as you adjust the tuner on your reciever to match the AM broadcaster's carrier frequency. Since many broadcast AM with a side band to the left of the carrier and to the right of the carrier you will here the change in tone as you approach the carrier frequency from either end. 

Lastly, the reciever tunes well below the HF region into and below the AM commercial broadcast band. You can listen here too. Here I 'd recommend using a simple to make magnetic loop antenna because the frequency length of the associated stations in this area of the spectrum are so long that long wire antennas that will receive their signal are impractical to put in place.

Have fun, I do more listening then transmitting and what I described is what I am using with darn good success.

On Fri, Jun 22, 2018, 4:43 AM sridhar <vu3pen@...> wrote:
I had ubitx ,currently using for RX Only ,its my first HF set ,Ubitx having 3 Mhz to  30 Mhz Frequency ,
1)Can i use this for Normal Radio RX i.e SW , i am able here radio but audio is not able to recognize. 
2)  what changes do need to do in this set to added any component to get full audio from SW frequency 



de 
vu3pen
sridhar 

Mike aka KC2WVB <rb5363@...>
 

The tuner I mentioned is actually a MFJ 16010 not 1600 as I initially indicated. It is very inexpensive and probably no more than $60. This type of tuner is easy to build if your so inclined. It only requires a variable capacitor and a hand wound inductor, coil, with taps spaced along its length. The taps and the variable capacitor adjust this LC circuit to match the signal of interest. 


On Fri, Jun 22, 2018, 5:40 AM R. Michael Boyer <rb5363@...> wrote:
OK, Sure you can listen to what you refer to as normal Shortwave because the radio's reciever covers the entire High Frequency spectrum. You will need an antenna system that allows you to tune the section of the spectrum your interested in listening to and adjust its tuning as you slide up or down the band. A 58 foot piece of wire that runs vertically for 17 feet before it bends at a right angle for the rest of its length coupled to a inexpensive MFJ 1600 long wire tuner works extremely well when the tuner and reciever are grounded to something like a cold water pipe.

The AM stations will sound a bit weird at first because if your not right on their carrier frequency the difference is heard as a high pitched tone that progressively becomes lower and goes to zero as you adjust the tuner on your reciever to match the AM broadcaster's carrier frequency. Since many broadcast AM with a side band to the left of the carrier and to the right of the carrier you will here the change in tone as you approach the carrier frequency from either end. 

Lastly, the reciever tunes well below the HF region into and below the AM commercial broadcast band. You can listen here too. Here I 'd recommend using a simple to make magnetic loop antenna because the frequency length of the associated stations in this area of the spectrum are so long that long wire antennas that will receive their signal are impractical to put in place.

Have fun, I do more listening then transmitting and what I described is what I am using with darn good success.

On Fri, Jun 22, 2018, 4:43 AM sridhar <vu3pen@...> wrote:
I had ubitx ,currently using for RX Only ,its my first HF set ,Ubitx having 3 Mhz to  30 Mhz Frequency ,
1)Can i use this for Normal Radio RX i.e SW , i am able here radio but audio is not able to recognize. 
2)  what changes do need to do in this set to added any component to get full audio from SW frequency 



de 
vu3pen
sridhar 

Mike aka KC2WVB <rb5363@...>
 

One last thing. The length of wire I mentioned comes from someone that spent a lot of time analyzing this type of antenna and 58 feet is one of many lengths that avoid being equal to a half wave on any of the HF bands. Therefore in theory it will tune to any band you want to listen to. I chose 58 feet because of space limitations but there are other lengths that would work well too. Additionally my antenna rises 17 feet before making the right angle bend because of practical concerns and from listening as a measure of effectiveness it was a good choice perhaps because it receives well signals that are vertically polarized or horizontally polarized.


On Fri, Jun 22, 2018, 5:56 AM Mike aka KC2WVB <rb5363@...> wrote:
The tuner I mentioned is actually a MFJ 16010 not 1600 as I initially indicated. It is very inexpensive and probably no more than $60. This type of tuner is easy to build if your so inclined. It only requires a variable capacitor and a hand wound inductor, coil, with taps spaced along its length. The taps and the variable capacitor adjust this LC circuit to match the signal of interest. 

On Fri, Jun 22, 2018, 5:40 AM R. Michael Boyer <rb5363@...> wrote:
OK, Sure you can listen to what you refer to as normal Shortwave because the radio's reciever covers the entire High Frequency spectrum. You will need an antenna system that allows you to tune the section of the spectrum your interested in listening to and adjust its tuning as you slide up or down the band. A 58 foot piece of wire that runs vertically for 17 feet before it bends at a right angle for the rest of its length coupled to a inexpensive MFJ 1600 long wire tuner works extremely well when the tuner and reciever are grounded to something like a cold water pipe.

The AM stations will sound a bit weird at first because if your not right on their carrier frequency the difference is heard as a high pitched tone that progressively becomes lower and goes to zero as you adjust the tuner on your reciever to match the AM broadcaster's carrier frequency. Since many broadcast AM with a side band to the left of the carrier and to the right of the carrier you will here the change in tone as you approach the carrier frequency from either end. 

Lastly, the reciever tunes well below the HF region into and below the AM commercial broadcast band. You can listen here too. Here I 'd recommend using a simple to make magnetic loop antenna because the frequency length of the associated stations in this area of the spectrum are so long that long wire antennas that will receive their signal are impractical to put in place.

Have fun, I do more listening then transmitting and what I described is what I am using with darn good success.

On Fri, Jun 22, 2018, 4:43 AM sridhar <vu3pen@...> wrote:
I had ubitx ,currently using for RX Only ,its my first HF set ,Ubitx having 3 Mhz to  30 Mhz Frequency ,
1)Can i use this for Normal Radio RX i.e SW , i am able here radio but audio is not able to recognize. 
2)  what changes do need to do in this set to added any component to get full audio from SW frequency 



de 
vu3pen
sridhar 

iz oos
 

You might also opt for a 9:1unun for HF (450:50ohm) and a random wire which are inexpensive and easier than a tuner. The wire can be put along a fiberglass fishing rod or put as a sloper if you use a tree or another support.


Il 22/giu/2018 12:19, "Mike aka KC2WVB" <rb5363@...> ha scritto:
One last thing. The length of wire I mentioned comes from someone that spent a lot of time analyzing this type of antenna and 58 feet is one of many lengths that avoid being equal to a half wave on any of the HF bands. Therefore in theory it will tune to any band you want to listen to. I chose 58 feet because of space limitations but there are other lengths that would work well too. Additionally my antenna rises 17 feet before making the right angle bend because of practical concerns and from listening as a measure of effectiveness it was a good choice perhaps because it receives well signals that are vertically polarized or horizontally polarized.

On Fri, Jun 22, 2018, 5:56 AM Mike aka KC2WVB <rb5363@...> wrote:
The tuner I mentioned is actually a MFJ 16010 not 1600 as I initially indicated. It is very inexpensive and probably no more than $60. This type of tuner is easy to build if your so inclined. It only requires a variable capacitor and a hand wound inductor, coil, with taps spaced along its length. The taps and the variable capacitor adjust this LC circuit to match the signal of interest. 

On Fri, Jun 22, 2018, 5:40 AM R. Michael Boyer <rb5363@...> wrote:
OK, Sure you can listen to what you refer to as normal Shortwave because the radio's reciever covers the entire High Frequency spectrum. You will need an antenna system that allows you to tune the section of the spectrum your interested in listening to and adjust its tuning as you slide up or down the band. A 58 foot piece of wire that runs vertically for 17 feet before it bends at a right angle for the rest of its length coupled to a inexpensive MFJ 1600 long wire tuner works extremely well when the tuner and reciever are grounded to something like a cold water pipe.

The AM stations will sound a bit weird at first because if your not right on their carrier frequency the difference is heard as a high pitched tone that progressively becomes lower and goes to zero as you adjust the tuner on your reciever to match the AM broadcaster's carrier frequency. Since many broadcast AM with a side band to the left of the carrier and to the right of the carrier you will here the change in tone as you approach the carrier frequency from either end. 

Lastly, the reciever tunes well below the HF region into and below the AM commercial broadcast band. You can listen here too. Here I 'd recommend using a simple to make magnetic loop antenna because the frequency length of the associated stations in this area of the spectrum are so long that long wire antennas that will receive their signal are impractical to put in place.

Have fun, I do more listening then transmitting and what I described is what I am using with darn good success.

On Fri, Jun 22, 2018, 4:43 AM sridhar <vu3pen@...> wrote:
I had ubitx ,currently using for RX Only ,its my first HF set ,Ubitx having 3 Mhz to  30 Mhz Frequency ,
1)Can i use this for Normal Radio RX i.e SW , i am able here radio but audio is not able to recognize. 
2)  what changes do need to do in this set to added any component to get full audio from SW frequency 



de 
vu3pen
sridhar 

sridhar
 

thx for valuable suggestions , i am also using the wire  antenna to  receive SW RX  ,  40 feet on AIR , then 40 vertical means total 80 feet is using , the wire is normal AC wire used for the house internal wring , for the same wire if i put 12 band normal radio , the audio is coming .
(I will try with 58 feet also in air later )

But my question i in UBITX set how can i receive SW  frequency 3 to 30 Mhz Stations ? for got the antenna which i am feeding i had many options to feed the antenna 

de 
vu3pen
sridhar

 

Sridhar,

Your question is "how to receive broadcast AM stations".

Without mods, you can carefully tune the station till the audio sounds clear. As the xtal filter is narrow
the sound will not be as good as a normal radio.

Raj

At 22/06/2018, you wrote:

But my question i in UBITX set how can i receive SW frequency 3 to 30 Mhz Stations ? for got the antenna which i am feeding i had many options to feed the antenna

de
vu3pen
sridhar

Mike aka KC2WVB <rb5363@...>
 

I guess I don't understand because to receive 3 through 30 Mhz aside from an antenna you simply turn the knob on the VFO and with this radio if your in 'say' 7 Mhz and you want to listen to 3 Mhz then press the encoder to enter the menu. Follow the menu's change frequency prompts an you easily get to 3 Mhz otherwise it takes a lot of turning of the knob to lower from 7 to 3.


On Fri, Jun 22, 2018, 7:14 AM sridhar <vu3pen@...> wrote:
thx for valuable suggestions , i am also using the wire  antenna to  receive SW RX  ,  40 feet on AIR , then 40 vertical means total 80 feet is using , the wire is normal AC wire used for the house internal wring , for the same wire if i put 12 band normal radio , the audio is coming .
(I will try with 58 feet also in air later )

But my question i in UBITX set how can i receive SW  frequency 3 to 30 Mhz Stations ? for got the antenna which i am feeding i had many options to feed the antenna 

de 
vu3pen
sridhar

iz oos
 

You have to press the vfo choose the band eg 14mhz and then using the vfo again. I have the original firmware version 3 installed and once you get acquainted it is somehow fast albeit a bit erratic.


Il 22/giu/2018 17:35, "Mike aka KC2WVB" <rb5363@...> ha scritto:
I guess I don't understand because to receive 3 through 30 Mhz aside from an antenna you simply turn the knob on the VFO and with this radio if your in 'say' 7 Mhz and you want to listen to 3 Mhz then press the encoder to enter the menu. Follow the menu's change frequency prompts an you easily get to 3 Mhz otherwise it takes a lot of turning of the knob to lower from 7 to 3.

On Fri, Jun 22, 2018, 7:14 AM sridhar <vu3pen@...> wrote:
thx for valuable suggestions , i am also using the wire  antenna to  receive SW RX  ,  40 feet on AIR , then 40 vertical means total 80 feet is using , the wire is normal AC wire used for the house internal wring , for the same wire if i put 12 band normal radio , the audio is coming .
(I will try with 58 feet also in air later )

But my question i in UBITX set how can i receive SW  frequency 3 to 30 Mhz Stations ? for got the antenna which i am feeding i had many options to feed the antenna 

de 
vu3pen
sridhar

Mike aka KC2WVB <rb5363@...>
 

Sridhar, I understand your post now. Your not asking how to receive AM broadcast signals rather your asking how to improve the audio quality of the AM signals your receiving. Right?

If you think about the difference between AM and SSB audio that is mixed with a carrier to create the hetrodynes that radiate over the air then what is notable is that AM allows for 5KHz of audio and SSB allows for roughly 2.7 to 3 KHz of audio. The reason for the difference is the power is, in a sense, more concentrated with respect to the SSB signal and it will travel further for an equal amount of total power. Hence your reciever has a narrower filter than an AM radio's reciever because it does not need to hear 5KHz to the left and right of the carrier. 

The downside is that when you use the SSB reciever to listen to AM broadcasts the audio will not be as full bodied as it would if the filter was wider. If you want to change the filter you would have to isolate the parts of the radio that form the filter and make the necessary changes. If you did, it would not be a bad idea to make the filter selectable as in most modern all-mode receivers so that you can select what is best for CW, SSB and finally AM. 

For myself, I am not that picky and listen to AM with the SSB filter if for no other reason than its a lot of work to bring about such a change. So, I can't tell you precisely what other than the filter would need altered.

On Fri, Jun 22, 2018, 4:43 AM sridhar <vu3pen@...> wrote:
I had ubitx ,currently using for RX Only ,its my first HF set ,Ubitx having 3 Mhz to  30 Mhz Frequency ,
1)Can i use this for Normal Radio RX i.e SW , i am able here radio but audio is not able to recognize. 
2)  what changes do need to do in this set to added any component to get full audio from SW frequency 



de 
vu3pen
sridhar 

sridhar
 

Mike

thx for tech inputs , yes i got the details from this post 
AM allows for 5KHz of audio and SSB allows for roughly 2.7 to 3 KHz of audio
to change this filters required 

thx 
de
vu3pen
sridhar 

Mike aka KC2WVB <rb5363@...>
 

Exactly!

I know our language difference made this take a while to get to the root of things because not being a native English speaker you selected words that were not well defined enough to strictly express your question but hats off to you because I don't speak your native language at all.


On Fri, Jun 22, 2018, 3:50 PM sridhar <vu3pen@...> wrote:
Mike

thx for tech inputs , yes i got the details from this post 
AM allows for 5KHz of audio and SSB allows for roughly 2.7 to 3 KHz of audio
to change this filters required 

thx 
de
vu3pen
sridhar 

Ralph Mowery
 

While most AM is set up for a 6 KHz of audio, a side band filter of slightly over 2 KHz will usually allow voice through well enough to be understood.  The music will sound clipped or somewhat distorted as it often has higher audio frequencies than  most taking voices.

The filter in most of the ubitx is really too narrow to suit me as I only operate ssb with it.  I changed out the 5  100pf capacitors in the crystal filter to 82 pf ( I think that is the standard value).  That broadened the filter in my ubitx from about 1700 hz to about 2300 hz.  Makes the audio sound much better for me.

One thing not discussed is that while AM often has the 6 khz filter, it only needs to be about half that when using a ssb filter as you are only using one sideband instead of both .  So around 3 khz would be good for AM.

de ku4pt





On Fri, Jun 22, 2018 at 3:50 PM, sridhar <vu3pen@...> wrote:
Mike

thx for tech inputs , yes i got the details from this post 
AM allows for 5KHz of audio and SSB allows for roughly 2.7 to 3 KHz of audio
to change this filters required 

thx 
de
vu3pen
sridhar 
_._,_._,

Mike aka KC2WVB <rb5363@...>
 

Ralph, 
Thanks, you did the calculations so a change is now simply swap out. I knew the filter was narrow but not that narrow. I guess they aimed at between ideal for CW and SSB by selecting as is. 
I don't have the stuff required for guaranteeing success when swapping out surface mounted capacitors. If I did I might make the change. 
I run my audio into the line in on a hi-fi system and can make the AM sound well enough to listen to by making audio adjustments, but I can see where it would be a pain in the arse to listen to the AM off a tiny 8 ohm speaker especially when it's frequency range is limited like it is.

On Jun 22, 2018 4:16 PM, "Ralph Mowery" <rmowery42@...> wrote:
While most AM is set up for a 6 KHz of audio, a side band filter of slightly over 2 KHz will usually allow voice through well enough to be understood.  The music will sound clipped or somewhat distorted as it often has higher audio frequencies than  most taking voices.

The filter in most of the ubitx is really too narrow to suit me as I only operate ssb with it.  I changed out the 5  100pf capacitors in the crystal filter to 82 pf ( I think that is the standard value).  That broadened the filter in my ubitx from about 1700 hz to about 2300 hz.  Makes the audio sound much better for me.

One thing not discussed is that while AM often has the 6 khz filter, it only needs to be about half that when using a ssb filter as you are only using one sideband instead of both .  So around 3 khz would be good for AM.

de ku4pt





On Fri, Jun 22, 2018 at 3:50 PM, sridhar <vu3pen@...> wrote:
Mike

thx for tech inputs , yes i got the details from this post 
AM allows for 5KHz of audio and SSB allows for roughly 2.7 to 3 KHz of audio
to change this filters required 

thx 
de
vu3pen
sridhar 
_._,_._,


Philip
 

I can receive BBC Radio Four on 198 Khz with mine.

Philip G7JUR

Ralph Mowery
 

I did not really do much in the way of calculating.  I do have the equipment to check it our.  One way was to feed in a 1000 Hz audio tone into the mic input.  Then measure the output power.  Then go up and down in frequency to where the power makes a big drop off.  

I know that by lowering the value of the capacitors the filter gets wider and going up in value the filter gets narrower.  The first attempt was around 68 pf (or whatever the standard value is near that).  That made the filter way too wide,so I put in the 80 some and that put it close enough for me.

Even going into a hifi amp it will be difficult to make the music sound very good.  If the filter cuts out the highs and lows before it gets to the demodulation part, about all you can do is use an  equalizer and run the audio from less than 500 hz way up and the audio above 1800 way up as there is almost no audio outside 500 hz to 1800 hz.

As the ubitx is, it is a great piece of engineering, but it is also easy to make changes to for anyone that has a bit of equipment and know how.  Many have published their modifications so that people like me only need to do them.

de ku4pt


On Fri, Jun 22, 2018 at 5:41 PM, Mike aka KC2WVB <rb5363@...> wrote:
Ralph, 
Thanks, you did the calculations so a change is now simply swap out. I knew the filter was narrow but not that narrow. I guess they aimed at between ideal for CW and SSB by selecting as is. 
I don't have the stuff required for guaranteeing success when swapping out surface mounted capacitors. If I did I might make the change. 
I run my audio into the line in on a hi-fi system and can make the AM sound well enough to listen to by making audio adjustments, but I can see where it would be a pain in the arse to listen to the AM off a tiny 8 ohm speaker especially when it's frequency range is limited like it is.

On Jun 22, 2018 4:16 PM, "Ralph Mowery" <rmowery42@...> wrote:
While most AM is set up for a 6 KHz of audio, a side band filter of slightly over 2 KHz will usually allow voice through well enough to be understood.  The music will sound clipped or somewhat distorted as it often has higher audio frequencies than  most taking voices.

The filter in most of the ubitx is really too narrow to suit me as I only operate ssb with it.  I changed out the 5  100pf capacitors in the crystal filter to 82 pf ( I think that is the standard value).  That broadened the filter in my ubitx from about 1700 hz to about 2300 hz.  Makes the audio sound much better for me.

One thing not discussed is that while AM often has the 6 khz filter, it only needs to be about half that when using a ssb filter as you are only using one sideband instead of both .  So around 3 khz would be good for AM.

de ku4pt


_._,_._,_


Joel Fournol
 

i receive gold radio on 1548 khz in center brittany work fine joel f6chtthe sound is very well



Le 22/06/2018 à 23:45, Philip a écrit :
I can receive BBC Radio Four on 198 Khz with mine.

Philip G7JUR

iz oos
 

The frequency response of the second IF filters of the Ubitx vary from unit to unit depending also where the BFO is set. My unit for example is about 2khz wide filtering out frequencies below 700hz. This it is very good for speech either ssb or AM/CW. In general the less selective/worse the receiver is the better and the less fatiguing is the listening to AM broadcasts. For AM those large ugly portables with HF shine. The Ubitx sounds more a communication or military receiver, at least my unit. In general a 6khz wide filter allow just 3khz frequency response, which is not much more than the usual Ubitx. If the receiver has a passband offset control (PBT) you can possibly recover all the 6khz. In any case most large portable that have no PBT, the filter is so wide you have a more pleasant audio. To have that wide filters in the Ubitx maybe one could remove most of the crystals in the second IF.


Il 23/giu/2018 00:09, "Ralph Mowery" <rmowery42@...> ha scritto:
I did not really do much in the way of calculating.  I do have the equipment to check it our.  One way was to feed in a 1000 Hz audio tone into the mic input.  Then measure the output power.  Then go up and down in frequency to where the power makes a big drop off.  

I know that by lowering the value of the capacitors the filter gets wider and going up in value the filter gets narrower.  The first attempt was around 68 pf (or whatever the standard value is near that).  That made the filter way too wide,so I put in the 80 some and that put it close enough for me.

Even going into a hifi amp it will be difficult to make the music sound very good.  If the filter cuts out the highs and lows before it gets to the demodulation part, about all you can do is use an  equalizer and run the audio from less than 500 hz way up and the audio above 1800 way up as there is almost no audio outside 500 hz to 1800 hz.

As the ubitx is, it is a great piece of engineering, but it is also easy to make changes to for anyone that has a bit of equipment and know how.  Many have published their modifications so that people like me only need to do them.

de ku4pt


On Fri, Jun 22, 2018 at 5:41 PM, Mike aka KC2WVB <rb5363@...> wrote:
Ralph, 
Thanks, you did the calculations so a change is now simply swap out. I knew the filter was narrow but not that narrow. I guess they aimed at between ideal for CW and SSB by selecting as is. 
I don't have the stuff required for guaranteeing success when swapping out surface mounted capacitors. If I did I might make the change. 
I run my audio into the line in on a hi-fi system and can make the AM sound well enough to listen to by making audio adjustments, but I can see where it would be a pain in the arse to listen to the AM off a tiny 8 ohm speaker especially when it's frequency range is limited like it is.

On Jun 22, 2018 4:16 PM, "Ralph Mowery" <rmowery42@...> wrote:
While most AM is set up for a 6 KHz of audio, a side band filter of slightly over 2 KHz will usually allow voice through well enough to be understood.  The music will sound clipped or somewhat distorted as it often has higher audio frequencies than  most taking voices.

The filter in most of the ubitx is really too narrow to suit me as I only operate ssb with it.  I changed out the 5  100pf capacitors in the crystal filter to 82 pf ( I think that is the standard value).  That broadened the filter in my ubitx from about 1700 hz to about 2300 hz.  Makes the audio sound much better for me.

One thing not discussed is that while AM often has the 6 khz filter, it only needs to be about half that when using a ssb filter as you are only using one sideband instead of both .  So around 3 khz would be good for AM.

de ku4pt


Mike aka KC2WVB <rb5363@...>
 

Yes, the UBitx is a nice piece of engineering. Hats off to the developers.

For myself, I don't listen to AM broadcasts for their music content rather I listen to the BBC and other foreign stations to hear views from abroad. 

A long time ago an EE friend of mine introduced me to reel to reel half speed masters and I was a convert the moment I heard the difference. I still remember how startled I was by what I had been missing. The tapes of course are pretty much a thing of the past so I had to make a choice between vinyl or a digital format such as the Sony/Phillips Super Audio CD. I chose the later and it offers some nice advantages over vinyl in that you can turn compression off and experience the full dynamic range of the music being played. Of course no format will sound good if the sound engineering is lackluster so buyer beware is always a consideration prior to spending upwards to $30 on a purchase.

It's too bad in my opinion that quality in music reproduction has seemed to take a back seat to other interests and it is certainly an area where newer is not equivalent to acoustically better. I am just thankful that there are enough audiophiles to allow quality to still be available.

On Sat, Jun 23, 2018, 5:15 AM iz oos <and2oosiz2@...> wrote:

The frequency response of the second IF filters of the Ubitx vary from unit to unit depending also where the BFO is set. My unit for example is about 2khz wide filtering out frequencies below 700hz. This it is very good for speech either ssb or AM/CW. In general the less selective/worse the receiver is the better and the less fatiguing is the listening to AM broadcasts. For AM those large ugly portables with HF shine. The Ubitx sounds more a communication or military receiver, at least my unit. In general a 6khz wide filter allow just 3khz frequency response, which is not much more than the usual Ubitx. If the receiver has a passband offset control (PBT) you can possibly recover all the 6khz. In any case most large portable that have no PBT, the filter is so wide you have a more pleasant audio. To have that wide filters in the Ubitx maybe one could remove most of the crystals in the second IF.


Il 23/giu/2018 00:09, "Ralph Mowery" <rmowery42@...> ha scritto:
I did not really do much in the way of calculating.  I do have the equipment to check it our.  One way was to feed in a 1000 Hz audio tone into the mic input.  Then measure the output power.  Then go up and down in frequency to where the power makes a big drop off.  

I know that by lowering the value of the capacitors the filter gets wider and going up in value the filter gets narrower.  The first attempt was around 68 pf (or whatever the standard value is near that).  That made the filter way too wide,so I put in the 80 some and that put it close enough for me.

Even going into a hifi amp it will be difficult to make the music sound very good.  If the filter cuts out the highs and lows before it gets to the demodulation part, about all you can do is use an  equalizer and run the audio from less than 500 hz way up and the audio above 1800 way up as there is almost no audio outside 500 hz to 1800 hz.

As the ubitx is, it is a great piece of engineering, but it is also easy to make changes to for anyone that has a bit of equipment and know how.  Many have published their modifications so that people like me only need to do them.

de ku4pt


On Fri, Jun 22, 2018 at 5:41 PM, Mike aka KC2WVB <rb5363@...> wrote:
Ralph, 
Thanks, you did the calculations so a change is now simply swap out. I knew the filter was narrow but not that narrow. I guess they aimed at between ideal for CW and SSB by selecting as is. 
I don't have the stuff required for guaranteeing success when swapping out surface mounted capacitors. If I did I might make the change. 
I run my audio into the line in on a hi-fi system and can make the AM sound well enough to listen to by making audio adjustments, but I can see where it would be a pain in the arse to listen to the AM off a tiny 8 ohm speaker especially when it's frequency range is limited like it is.

On Jun 22, 2018 4:16 PM, "Ralph Mowery" <rmowery42@...> wrote:
While most AM is set up for a 6 KHz of audio, a side band filter of slightly over 2 KHz will usually allow voice through well enough to be understood.  The music will sound clipped or somewhat distorted as it often has higher audio frequencies than  most taking voices.

The filter in most of the ubitx is really too narrow to suit me as I only operate ssb with it.  I changed out the 5  100pf capacitors in the crystal filter to 82 pf ( I think that is the standard value).  That broadened the filter in my ubitx from about 1700 hz to about 2300 hz.  Makes the audio sound much better for me.

One thing not discussed is that while AM often has the 6 khz filter, it only needs to be about half that when using a ssb filter as you are only using one sideband instead of both .  So around 3 khz would be good for AM.

de ku4pt