EMRFD Message Archive 1074

Message Date From Subject
1074 2007-09-30 09:02:23 bkopski How's My Audio?
Hi All,

I'm new to HF and have been trying my hand at HB 20M QRP SSB for about
a year. It took much of that time to get my first ever transceiver
going - it's the chassis full of subcircuit blocks in the posted
photo. I can push just short of 1W pk out of it but I know that at
this level it is distorting. While I've typically received "good
audio" reports I've always wondered how I really sounded. What I
needed was another Rx to listen to my own signal. What I needed was a
substitute voice into my Tx mike. The test setup to do this - shown in
the photo - sprang forth from EMRFD Fig. 8.7, some e-mail comments from
Wes, W3ZOI, and some other hardware. Overall, this setup works great,
and I've learned that I do indeed need to work on my audio a bit

Fig. 8.7 is a very simple DC Rx. I borrowed the Xtal Osc and Product
Detector portions of the schematic (the interconnected pc brd.
subassemblies in the detail photo) and ran the detected output into an
amplified speaker (black box to the right rear of the rig). The
earphone jack of a portable radio cabled to my mike jack supplied the
voice. The rig's rf output is cabled through a dummy load / attenuator
into my test Rx input - levels 60 to 90 dB down from the Tx output
worked well depending on the audio gain setting.

The Xtal Osc LO uses a 14.31818 crystal (Mouser) and so I just tune my
VFO to use that test-Rx frequency. I found it best to use a strong
local FM "talk radio" type station as signal source - this audio is
much like typical voice on our air. I also discovered my rig's Xtal
filter is a bit narrow to handle wider band audio such as with music or
female voices - one has to keep one's hand on the VFO knob to track
such content - but this material would not normally be of interest
anyway. Also, now I have a real appreciation of how my rig's
adjustable audio limiter messes up received sound quality!

The speaker shown (old, battery powered, from Radio Shack) has lots of
gain and easily handles this chore. I also tried two different kinds
of wall-wart powered computer speakers - these did not have enough gain
so I fitted a 40 - 50 dB audio amplifier between the product detector
and the speaker - this was then just as good as my black box speaker.

I suspect there are many rigs out there - HB and maybe otherwise -
whose audio may be less than the best but yet not really known. I
think this is most likely found in HB stuff, and I also get the
impression that most hams on the receiving end are tempted to give good
audio reports - i.e. - to act as a very friendly human filters no
matter reality. I'm pretty sure now this has been the case with my
rig. Anyway, if you want to know what your rig sounds like - for real -
I can heartily recommend this test approach to finding out - it's
quick and cheap and I'm sure glad I tried it - even though I now have
rig-work to do. (Hey - it's all fun anyway - right?)

Cordially and 73,
1076 2007-09-30 17:39:50 Allison Parent Re: How's My Audio?
1077 2007-10-01 09:55:11 Hari G Re: How's My Audio?
For testing i have tried hearing me on a  different radio while modulating on the test rig, its an impossible task i could never make out how i sound like ! 
 This is definitely a good input i will try that in my new radio (40M only Belthorn) which is on the bench with a occationally unstable power amp.
Best Regards

On 10/1/07, Allis
1078 2007-10-01 11:40:38 Kevin Purcell Re: How's My Audio?
Are you using headphones?

Failing that record the test signal from the radio and play it back
later. I find this is often more useful for critical listening.

1079 2007-10-01 19:26:31 Allison Parent Re: How's My Audio?
1080 2007-10-02 10:07:02 Nick Kennedy Re: How's My Audio?
I haven't built a monitoring receiver, but I did do some stuff with
test audio while designing a 60 meter SSB transmitter a couple years

Monitoring my own voice "real time" was difficult, and the lash up
introduced complexities of RF pickup and so on, into my breadboarded

So I made up an audio test CD. First I made a loop of my voice
yelling out a CQ Contest thing, using an audio software program to
create the repetitions of the original short CQ track and getting up
to about three minutes. As I got into it, I added more tracks at
different levels, plus pink noise tracks and tracks of two test
tones. All very handy and easily accessible.

There were several technical advantages. I was using a
portable "DiscMan" type CD player on battery power, so no ground
loops to the mains, and my patch cord from CD player to rig was
about 4 inches long, minimizing RF pickup potential. Since I had
line outputs driving a microphone preamp, I did have to include a
resistive pad attenuator up front.

73--Nick, WA5BDU