[G3XBM] Micro 40 - 40m DSB transceiver

[G3XBM via rec.radio.amateur.moderated Admin]

Roger G3XBM's Amateur Radio Blog

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Micro 40 - 40m DSB transceiver

Posted: 24 Jan 2015 10:06 AM PST
http://g3xbm-qrp.blogspot.com/2015/01/micro-40-40m-dsb-transceiver.html

See http://home.alphalink.com.au/~parkerp/projects/projmicro40.htm .

Also:
https://aa7ee.wordpress.com/2013/10/19/the-vk3ye-micro-40-dsb-transceiver/ .

Well designed DSB transceivers are much simpler than SSB rigs as no SSB
filters and mixing to final frequency is needed. They must not be
over-driven to avoid a spreading signal. The PA needs to be linear too.
These issues being carefully considered, you end up with a rig that has
the same bandwidth as an AM rig but with a suppressed carrier. DSB
transmitters are usually received as an SSB signal. The downside is that
if a simple direct-conversion receiver is used then there is no rejection
of stations sitting on the other sideband. So, they are best on quieter
bands, rather than busy HF bands. Bands like 10m, 6m and 4m are probably
good candidates.

Although not impossible, it is quite difficult to demodulate a DSB signal
on a simple direct-conversion receiver. DSB rigs are ideal as simple
transceivers to communicate with SSB rigs.

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10m USA WSPR spots of my 500mW beacon today

Posted: 24 Jan 2015 01:41 PM PST
http://g3xbm-qrp.blogspot.com/2015/01/10m-usa-wspr-spots-of-my-500mw-beacon.html

WG2Z (5600km) was the first USA station to spot my 500mW 10m WSPR beacon
today at 1302z. I see that FR1GZ (9724km) on Reunion Is, South Indian
Ocean, has already spotted me a couple of times already on 10m WSPR today!

UPDATE 1728z: KU4QI (6406km) was the last to spot my 500mW 10m
WSPR-AXE-CW WSPR beacon at 1708z. There is still a chance others will spot
me later.

UPDATE 2110z: The last USA station to spot me was K9AN (6505km) over an
hour later at 1838z. It all depends who stays around and who is active! I
was surprised.

UPDATE 2140z: I went QRT on 10m WSPR at 2112z. I have now QSYed to MF for
the night.

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G8HUH - multiple spots of my 5mW ERP on 472kHz WSPR

Posted: 24 Jan 2015 12:48 AM PST
http://g3xbm-qrp.blogspot.com/2015/01/g8huh-multiple-spots-of-my-5mw-erp-on.html

G8HUH (250km) in IO81 square has spotted me on 472kHz WSPR 16 times so far
today since the middle of the night.

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Sunspots

Posted: 24 Jan 2015 05:47 AM PST
http://g3xbm-qrp.blogspot.com/2015/01/sunspots_24.html

Sunspot number is up to 70 today and 10m propagation forecast to be "fair".

UPDATE 1346z: So far, the 10m band is behaving predictably.

[gareth]

"G3XBM via rec.radio.amateur.moderated Admin"
<rec-radio-amateur...@panix.com> wrote in message
news:047d7b5d612a20...@google.com...

>
> Although not impossible, it is quite difficult to demodulate a DSB signal
> on a simple direct-conversion receiver. DSB rigs are ideal as simple
> transceivers to communicate with SSB rigs.

The reason being that to resolve DSB, the injected carrier must have a
very close phase relationship with the original carrier, and at a certain
phase relationship (don't remember but probably 90 degrees) there's
no output at all!

Gareth G4SDW

[Michael Black]

It doesn't even have to get to the point where phase comes into play.

If you don't have it "zero beat" the two sidebands will not only sound odd
(because they aren't converting down to their original baseband) but the
two sidebands will clash with each other. If the carrier is in the right
place, both sidebands will convert to the exact same audio frequency. If
the carrier isn't right in the middle of those sidebands, the two
sidebands will convert to different audio frequencies, so it will sound
awful, at the very least.

Single sideband can be mistuned somewhat, all it sounds like is osmeone
talking in a higher or lower tone than "normal". But if an DSB signal is
demodulated with the carrier not right in the centre, the two sidebands
converted to audio interfere with each other. If the carrier is right in
the middle, they combine properly.

Synchronous detectors were originally created because of this, to properly
demodulate DSB with no carrier. Which is kind of odd, since in more
recent times synchronous detectors have become relatively common in
shortwave receivers, yet some or many of those designs likely don't work
with DSB no carrier. It depends on where the circuit is getting the
information to control the BFO.

There was a time when DSBsc demodulators were shown in the ham magazines,
the simple ones would square up and then double the incoming signal and
then divide it back down to the IF signal. Which always resulted in the
carrier being right in the middle between the sidebands.

But a synchronous detector was too much trouble, might as well use an SSB
receiver and convert the DSBsc signal to SSB inside the receiver. By the
time synchronous detectors were known, the move to receivers for SSB had
already started.

Of course, DSBsc has other advantages beyond the simple transmitter, a
proper demodulator makes use of the redundancy the two sidebands to
improve reception. If nothing else, it gets information from both
sidebands, yet allows one to switch between the two if interference is on
one sideband. A proper DSBsc system is more complicated at the receiver,
but has some advantages over SSB (though narrower bandwidth isn't one of
them).

Various shortwave broadcast stations have played with SSB for
transmitting, and often have had to fall back to SSB with reduced carrier,
since if they are playing music, they need the carrier to tell people
where the local BFO should be set; otherwise the music converts to the
wrong audio frequencies, and sounds way worse than a mistuned voice SSB
signal. Or they could put the other sideband back, but eliminate the
carrier. That way the unneeded carrier isn't transmitted (so more power
for the sidebands) but the extra sideband provides the information needed
to insert the local BFO right in the middle of the sidebands for proper
demdulation.

Michael

[Jerry Stuckle]

Wrong again, Gareth. Phase relationship is immaterial. It's hard to
demodulate because a direct-conversion receiver does not generally have
a means of injecting a carrier.

--
==================
Remove the "x" from my email address
Jerry, AI0K
jstu...@attglobal.net
==================

[FranK Turner-Smith G3VKI]

"gareth" <no....@thank.you.invalid> wrote in message
news:ma2gv9$2ac$1...@dont-email.me...

Why not just filter out one sideband and resolve it as SSB?
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk

[FranK Turner-Smith G3VKI]

"Michael Black" <et...@ncf.ca> wrote in message
news:alpine.LNX.2.02.1...@darkstar.example.org...

I believe there were some experiments a few years ago with stereo AM
broadcasts using different sidebands for each channel. Automatic carrier
reinsertion sounds like a problem, or was the carrier simply reduced and not
suppressed?
--
;-)

.
73 de Frank Turner-Smith G3VKI - mine's a pint.
.

http://turner-smith.co.uk

[Frank Turner-Smith G3VKI]

Sorry, pissed again. It was AM, full carrier, no BFO. Time for a another
drink.
--

[Michael Black]

On Mon, 26 Jan 2015, Jerry Stuckle wrote:

> On 1/25/2015 12:46 PM, gareth wrote:
>> "G3XBM via rec.radio.amateur.moderated Admin"
>> <rec-radio-amateur...@panix.com> wrote in message
>> news:047d7b5d612a20...@google.com...
>>>
>>> Although not impossible, it is quite difficult to demodulate a DSB signal
>>> on a simple direct-conversion receiver. DSB rigs are ideal as simple
>>> transceivers to communicate with SSB rigs.
>>
>> The reason being that to resolve DSB, the injected carrier must have a
>> very close phase relationship with the original carrier, and at a certain
>> phase relationship (don't remember but probably 90 degrees) there's
>> no output at all!
>>
>> Gareth G4SDW
>>
>>
>
> Wrong again, Gareth. Phase relationship is immaterial. It's hard to
> demodulate because a direct-conversion receiver does not generally have
> a means of injecting a carrier.
>

By definition a direct conversion receiver has a BFO, which is why they
aren't so good for receiving AM with carrier signals.

The term wasn't really used until 1968 when that article by Hayward
appeared in QST showing a receiver that used a schottky diode mixer and
called it a "direct conversion receiver". That's when simple receivers
changed from regenerative receivers (and the occasional simple superhet)
to direct conversion, that era lasting until home made ladder filters
flopped things back to simple superhets.

Michael

[Michael Black]

On Mon, 26 Jan 2015, FranK Turner-Smith G3VKI wrote:

> "gareth" <no....@thank.you.invalid> wrote in message
> news:ma2gv9$2ac$1...@dont-email.me...
>> "G3XBM via rec.radio.amateur.moderated Admin"
>> <rec-radio-amateur...@panix.com> wrote in message
>> news:047d7b5d612a20...@google.com...
>>> Although not impossible, it is quite difficult to demodulate a DSB signal
>>> on a simple direct-conversion receiver. DSB rigs are ideal as simple
>>> transceivers to communicate with SSB rigs.
>>
>> The reason being that to resolve DSB, the injected carrier must have a
>> very close phase relationship with the original carrier, and at a certain
>> phase relationship (don't remember but probably 90 degrees) there's
>> no output at all!
>>
> Why not just filter out one sideband and resolve it as SSB?

That is generally the point of using DSBsc. Since SSB receivers are now
common, using a DSB transmitter means a simpler transmitter compared to an
SSB transmitter, but no pesky carrier to waste power at the transmitter.
The only "cost" is double the bandwidth used. It was certainly done in
the earlier days of SSB, and I gather from articles many people didn't
notice the extra sideband.

But if you are building a DSB station, you then can't have a simple direct
conversion receiver if you hope to talk to similar stations. You'd need
an SSB receiver, either a superhet with an SSB filter, or a phasing method
receiver. Once you have that, the simplicity is gone, and you also might
as well apply such methods to the transmitter to get full SSB.

DSB works because most of the other stations will be SSB, so a simple
transmitter and receiver works.

Michael

[Michael Black]

And it was two independent sidebands, not DSB. So you couldn't get
information from the two sidebands to place the carrier right in the
middle since the sidebands carried different information.

That was one of the various schemes for AM stereo. I remember reading
about early experiments, you could use two am portables, tuning each a bit
off the centre frequency so each radio received one of the channels.
Since the FCC in the US changed their mind and allowed all methods to be
used, it's probably legal for AM broadcasters, but it wasn't the most
common system used. Actually I guess it is, just a modified version.

One reason Sony put a synchronous detector in their classic 2010 shortwave
portable was because they'd designed an IC for this method of AM stereo,
and since AM stereo never took off, they had the IC. And it just
happenened to be what wsa needed to demodulate DSB, the modern
equivalent of a phasing type "sideband slicer" with circuitry to lock the
carrier to the incoming signal. There has to be a method of turnig off
the locking, since the IC also works for demodulating SSB (and if the
carrier is set right, you could get LSB out of one channel and USB out of
the other). It's the same thing with the Motorola series of AM stereo
detectors.

I think for shortwave broadcasting, they've tried just about everything
except DSBsc. I gather our time station, CHU, uses a single sideband
signal with carrier, though I can't remember if it's reduced or not.

Michael

[Michael Black]

On Mon, 26 Jan 2015, Brian Reay wrote:

> "FranK Turner-Smith G3VKI" <g3...@turner-smith.co.uK> wrote:

>> "gareth" <no....@thank.you.invalid> wrote in message news:ma2gv9$2ac$1...@dont-email.me...
>>> "G3XBM via rec.radio.amateur.moderated Admin" >
>>> <rec-radio-amateur...@panix.com> wrote in message >
>>> news:047d7b5d612a20...@google.com...
>>>> Although not impossible, it is quite difficult to demodulate a DSB
>>>> signal >> on a simple direct-conversion receiver. DSB rigs are ideal as
>>>> simple >> transceivers to communicate with SSB rigs.
>>>
>>> The reason being that to resolve DSB, the injected carrier must have a
>>> very close phase relationship with the original carrier, and at a certain
>>> phase relationship (don't remember but probably 90 degrees) there's
>>> no output at all!
>>>
>> Why not just filter out one sideband and resolve it as SSB?
>

> While that would work, part of the idea of using DSB in amateur circles is
> to avoid the expense of filters.
>
> Gareth is correct, if the carrier is not inserted in the correct phase, the
> audio is suppressed. He did, however, miss-remember the angle for total
> suppression, it is 180 degrees. Hardly something to make an issue of.
>
> For those interested in the building of DSB radios, I recommend the
> Soldersmoke podcasts. DSB radios often get a mention. There are a couple
> of videos on YouTube by the host of the podcasts which some may find
> interesting.
>
I thuught we taught him all he knows about DSB in
rec.radio.amateur.homebrew.

I'm not sure, there are two Bill M's around, and I'm not sure which is
which. I know one of them was talking DSB some years back in the homebrew
newsgroup.

Michael

[Jerry Stuckle]

You're right - I was thinking about regenerative. Teaches me to not
answer so quickly :)

And BTW - in '68, most receivers were superhet, and had been for many
years. Regenerative receivers had long gone out of style (40's, maybe?
Before my time).

[edgard...@gmail.com]

Dear Gareth: You can receive DSB with a any receiver (Even a simple DC), if you transmit with an audio inverter in the premplifier. The receiver take both sidebands, but one is inverted and the other is OK. This procedure was developed by RCA in the 50's as alternative to the syncro detector.
Regards. Edgardo Maffia LU1AR

[gareth]

<edgard...@gmail.com> wrote in message
news:59de7e15-b0ad-4daf...@googlegroups.com...

Whereas what you say below is true, I believe you are describing in outline
the phasing
technique, whereas the discussion related to simple direct conversion.

Improvements on the phasing technique are the "3rd method" AKA "Weaver" RXs

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