Topics

Getting enough power to check SWR with BITx40

Scott
 

My son purchased a BITx40 and we thought it would be a good idea to check the SWR of his home made antenna before transmitting.
 
The problem we have run into is that his BITx40 only puts out a fraction of a Watt of power (.016 W) unless we are speaking into the microphone.  We are not able to use our SWR bridge with the low power.
 
1. Is this normal for a BITX40?
 
2. Assuming this is normal, is there a standard way to increase the power to the antenna for these types of measurements?  (I suppose we could set up a speaker next to the microphone to give consistent white noise or tone input.) 
 
Power output was determined by taking voltage measurements with a multimeter on the output leads of a 50 Ohm dummy load.
1.05V without speaking into the microphone (1.05V)^2 / 50 Ohm *.707 = .016 W (RMS power)
18V Loudly speaking into the microphone (18V)^2 / 50 Ohm *.707 = 4.58 W (RMS power)
 
Thanks,
Scott

R. Tyson
 

Hi Scott,
Sounds about right. The mic. is usually not very good and does better with either a replacement or mic. amp. to boost it up a bit.

Why not set up the antenna tuning by using the CW setting ? It will give a more consistent output than voice and make it easier to do.

Reg             G4NFR

Dale Parfitt
 

Hi Scott,

Ideally, there would be zero  output w/o voice in SSB mode. Use  CW mode, not SSB.

 

Regards & have fun.

Dale W4OP

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Scott
Sent: Sunday, May 17, 2020 10:45 AM
To: BITX20@groups.io
Subject: [BITX20] Getting enough power to check SWR with BITx40

 

My son purchased a BITx40 and we thought it would be a good idea to check the SWR of his home made antenna before transmitting.
 
The problem we have run into is that his BITx40 only puts out a fraction of a Watt of power (.016 W) unless we are speaking into the microphone.  We are not able to use our SWR bridge with the low power.
 
1. Is this normal for a BITX40?
 
2. Assuming this is normal, is there a standard way to increase the power to the antenna for these types of measurements?  (I suppose we could set up a speaker next to the microphone to give consistent white noise or tone input.) 

 

Power output was determined by taking voltage measurements with a multimeter on the output leads of a 50 Ohm dummy load.
1.05V without speaking into the microphone (1.05V)^2 / 50 Ohm *.707 = .016 W (RMS power)
18V Loudly speaking into the microphone (18V)^2 / 50 Ohm *.707 = 4.58 W (RMS power)
 
Thanks,
Scott

Gordon Gibby
 

When doing single side band, you are not supposed to see power when not speaking. 

The solution for that is either to use key down Morse code, or inject a tone into your microphone.   

For years, amateur radio operators have simply press the Morse code key down to generate a carrier output


On May 17, 2020, at 11:01, Dale Parfitt <PARINC1@...> wrote:



Hi Scott,

Ideally, there would be zero  output w/o voice in SSB mode. Use  CW mode, not SSB.

 

Regards & have fun.

Dale W4OP

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Scott
Sent: Sunday, May 17, 2020 10:45 AM
To: BITX20@groups.io
Subject: [BITX20] Getting enough power to check SWR with BITx40

 

My son purchased a BITx40 and we thought it would be a good idea to check the SWR of his home made antenna before transmitting.
 
The problem we have run into is that his BITx40 only puts out a fraction of a Watt of power (.016 W) unless we are speaking into the microphone.  We are not able to use our SWR bridge with the low power.
 
1. Is this normal for a BITX40?
 
2. Assuming this is normal, is there a standard way to increase the power to the antenna for these types of measurements?  (I suppose we could set up a speaker next to the microphone to give consistent white noise or tone input.) 

 

Power output was determined by taking voltage measurements with a multimeter on the output leads of a 50 Ohm dummy load.
1.05V without speaking into the microphone (1.05V)^2 / 50 Ohm *.707 = .016 W (RMS power)
18V Loudly speaking into the microphone (18V)^2 / 50 Ohm *.707 = 4.58 W (RMS power)
 
Thanks,
Scott

Evan Hand
 

Scott,
Yes, it is normal for all SSB transmitters to have no power out without any audio.  It is why they are more efficient than AM transmitters.  For most trancievers there is a CW mode that allows you to send a pure carrier when the CW key is pressed.  That is how I do tuning/SWR checks with my uBITX.  

I checked the BITX40 schematic and found no CW key input.  The only way that I can think of to do the equivalent would be to use a tone generator to feed either one or two tones into the microphone input.  Alternatively, you could use a tone generation program on a PC and hold the mic near the speaker to generate the tone.

Here is a single tone generator that is free
https://www.microsoft.com/en-us/p/tone-generator/9wzdncrdhjqn?activetab=pivot:overviewtab
I would recommend using 1,000 Hrz as the tone.

An actual owner of a BITX40 may have another way, as maybe there is a way to set up the transceiver for CW.

73
Evan
AC9TU

Bill Cromwell
 

Just as a suggestion you might use something like fldigi in it's CW mode and send the Morse signal that way. You may have to include a VOX switch id the BitX doesn't have that. It can be included in the interface to/from the computer sound card. It may be needed for using the digital modes anyway.

Using the push to talk in SSB with no audio input should produce no output just at the others have said. Between the balanced modulator and the filter you should be in the microwatt (or low millwatt) range with the carrier leakage.

73,

Bill KU8H

On 5/17/20 11:18 AM, Evan Hand wrote:
Scott,
Yes, it is normal for all SSB transmitters to have no power out without any audio.  It is why they are more efficient than AM transmitters.  For most trancievers there is a CW mode that allows you to send a pure carrier when the CW key is pressed.  That is how I do tuning/SWR checks with my uBITX.
I checked the BITX40 schematic and found no CW key input.  The only way that I can think of to do the equivalent would be to use a tone generator to feed either one or two tones into the microphone input. Alternatively, you could use a tone generation program on a PC and hold the mic near the speaker to generate the tone.
Here is a single tone generator that is free
https://www.microsoft.com/en-us/p/tone-generator/9wzdncrdhjqn?activetab=pivot:overviewtab
I would recommend using 1,000 Hrz as the tone.
An actual owner of a BITX40 may have another way, as maybe there is a way to set up the transceiver for CW.
73
Evan
AC9TU
--
bark less - wag more

Satish Chandorkar
 

Scott
You have not stated how you measured power across your dummy load.
Was it a RF probe or oscilloscope or anything else
Without knowing of this whatever calculations you are stating has no meaning

Satish
VU2SNK


On Sun, May 17, 2020 at 9:09 PM Bill Cromwell <wrcromwell@...> wrote:
Just as a suggestion you might use something like fldigi in it's CW mode
and send the Morse signal that way. You may have to include a VOX switch
id the BitX doesn't have that. It can be included in the interface
to/from the computer sound card. It may be needed for using the digital
modes anyway.

Using the push to talk in SSB with no audio input should produce no
output just at the  others have said. Between the balanced modulator and
the filter you should be in the microwatt (or low millwatt) range with
the carrier leakage.

73,

Bill  KU8H


On 5/17/20 11:18 AM, Evan Hand wrote:
> Scott,
> Yes, it is normal for all SSB transmitters to have no power out without
> any audio.  It is why they are more efficient than AM transmitters.  For
> most trancievers there is a CW mode that allows you to send a pure
> carrier when the CW key is pressed.  That is how I do tuning/SWR checks
> with my uBITX.
>
> I checked the BITX40 schematic and found no CW key input.  The only way
> that I can think of to do the equivalent would be to use a tone
> generator to feed either one or two tones into the microphone input. 
> Alternatively, you could use a tone generation program on a PC and hold
> the mic near the speaker to generate the tone.
>
> Here is a single tone generator that is free
> https://www.microsoft.com/en-us/p/tone-generator/9wzdncrdhjqn?activetab=pivot:overviewtab
> I would recommend using 1,000 Hrz as the tone.
>
> An actual owner of a BITX40 may have another way, as maybe there is a
> way to set up the transceiver for CW.
>
> 73
> Evan
> AC9TU
>

--
bark less - wag more



Arv Evans
 

Scott

If I understand what you are saying, this may be a misunderstanding of how SSB works.  
Ideally there would be no, or minimal, power output without audio input from the mike.
Audio input unbalances the balanced modulator and allows modulated carrier to go 
to the transmit stages.  Old-school way of testing SSB output was to use a two-tone 
audio oscillator to generate speech-like tones into the mike input.  For a pure carrier 
output you can insert a single audio tone into the mike input.  This will give you a CW-like 
output that is offset from the carrier frequency by the tone frequency.

Arv  K7HKL
_._


On Sun, May 17, 2020 at 8:45 AM Scott <sskroch@...> wrote:
My son purchased a BITx40 and we thought it would be a good idea to check the SWR of his home made antenna before transmitting.
 
The problem we have run into is that his BITx40 only puts out a fraction of a Watt of power (.016 W) unless we are speaking into the microphone.  We are not able to use our SWR bridge with the low power.
 
1. Is this normal for a BITX40?
 
2. Assuming this is normal, is there a standard way to increase the power to the antenna for these types of measurements?  (I suppose we could set up a speaker next to the microphone to give consistent white noise or tone input.) 
 
Power output was determined by taking voltage measurements with a multimeter on the output leads of a 50 Ohm dummy load.
1.05V without speaking into the microphone (1.05V)^2 / 50 Ohm *.707 = .016 W (RMS power)
18V Loudly speaking into the microphone (18V)^2 / 50 Ohm *.707 = 4.58 W (RMS power)
 
Thanks,
Scott

Scott
 

Thanks to every one that replied to my question.  I now understand that for single side band the power should be very low (or zero) with no microphone input (which is consistent with my observations).  My son and I can work out the details of how to get a signal into the radio for making the measurements.  I will take a look at implementing a CW mod for the BITx40, I have seen instructions for this online. Introducing a tone into the mic might get my son up and running the fastest.

Thanks,
Scott

 

Scott,

For years I've been using a free app for my iPhone called Tone Generator, it comes up outputting a 1000hz sine wave tone, I just put it by the mic and key up then make my tuner adjustments. It's been working great for a long time.

Joel
N6ALT

jim
 

Try a "two-tone tester" ..more consistant results than the "ahhhhj" method

Jim

On Sunday, May 17, 2020, 9:27:08 AM PDT, Scott <sskroch@...> wrote:


Thanks to every one that replied to my question.  I now understand that for single side band the power should be very low (or zero) with no microphone input (which is consistent with my observations).  My son and I can work out the details of how to get a signal into the radio for making the measurements.  I will take a look at implementing a CW mod for the BITx40, I have seen instructions for this online. Introducing a tone into the mic might get my son up and running the fastest.

Thanks,
Scott