Ideal ham receiver
 

I don't much like the receivers I've used in contemporary tranceivers
-- the general coverage synthisized open front end ones. (I hasten to
add I haven't used any of the $4000 rigs; can't afford them). But the
ones I have used seem plagued with near-signal desensitization, front
end overload, etc., and I suppose all that comes from putting the
selectivity so far downstream.

I'm almost tempted to get an old 75s4 and shut up, but I really don't
need another room heater, so, instead, I'm thinking of building my own
receiver along the lines laid down by the late Doug DeMaw in his _QRP
Notebook_. Single conversion 160m superhet with Collins mechanical
filters in the IF and a series of down-converters for the other bands.
Anybody got any experience with the DeMaw Design?

Jim, K5YUT

Ideal ham receiver
 

I think the main issue with the contemporary transceivers is covering DC to
daylight and trying to make the thing work. A single band design seems to
be a lot easier to make bulletproof.

Modern QRP design has advanced a lot since the DeMaw days, even over the
venerable 75s4. Take a look at designs by K8IQY or AD6A or N7VE and you
will find receivers that will be head and shoulders beyond anything that
W1FB ever dreamed of.

The front end overload issues on simple receivers seems to be largely
related to the use of the 602/612 mixer. The passive mixer, or Tayloe
mixer, designs seem to fare much better. The Elecraft K1 is the exception
that proves the rule; I suspect careful gain management may have something
to do with that.

KK7B has also written a LOT on receiver design, and his designs have a good
rep, but I've never used them so I can't comment from experience.

Doug's designs are fun, and sort of nostalgic, but if you are looking for
21st century performance, it isn't the place to look.

...

wrote in message
ups.com...
I don't much like the receivers I've used in contemporary tranceivers
-- the general coverage synthisized open front end ones. (I hasten to
add I haven't used any of the $4000 rigs; can't afford them). But the
ones I have used seem plagued with near-signal desensitization, front
end overload, etc., and I suppose all that comes from putting the
selectivity so far downstream.

I'm almost tempted to get an old 75s4 and shut up, but I really don't
need another room heater, so, instead, I'm thinking of building my own
receiver along the lines laid down by the late Doug DeMaw in his _QRP
Notebook_. Single conversion 160m superhet with Collins mechanical
filters in the IF and a series of down-converters for the other bands.
Anybody got any experience with the DeMaw Design?

Jim, K5YUT

Ideal ham receiver
 

Ideal ham receiver
 

Try Drake R4B and Softrock tuned to the first IF 5645 (?) you will get best
of both worlds. Switching before and after filters gives more options.

Yuri, K3BU

wrote in message
ups.com...
I don't much like the receivers I've used in contemporary tranceivers
-- the general coverage synthisized open front end ones. (I hasten to
add I haven't used any of the $4000 rigs; can't afford them). But the
ones I have used seem plagued with near-signal desensitization, front
end overload, etc., and I suppose all that comes from putting the
selectivity so far downstream.

I'm almost tempted to get an old 75s4 and shut up, but I really don't
need another room heater, so, instead, I'm thinking of building my own
receiver along the lines laid down by the late Doug DeMaw in his _QRP
Notebook_. Single conversion 160m superhet with Collins mechanical
filters in the IF and a series of down-converters for the other bands.
Anybody got any experience with the DeMaw Design?

Jim, K5YUT

Ideal ham receiver
 

) writes:
I don't much like the receivers I've used in contemporary tranceivers
-- the general coverage synthisized open front end ones. (I hasten to
add I haven't used any of the $4000 rigs; can't afford them). But the
ones I have used seem plagued with near-signal desensitization, front
end overload, etc., and I suppose all that comes from putting the
selectivity so far downstream.

I'm almost tempted to get an old 75s4 and shut up, but I really don't
need another room heater, so, instead, I'm thinking of building my own
receiver along the lines laid down by the late Doug DeMaw in his _QRP
Notebook_. Single conversion 160m superhet with Collins mechanical
filters in the IF and a series of down-converters for the other bands.
Anybody got any experience with the DeMaw Design?

Jim, K5YUT

But then you're just recreating something that is open to problems.

That sort of scheme was used to get a constant tuning range over each band,
and because synthesis wasn't easily applied.

But on anything other than the core band, you've got double conversion that
moves the selectiving past two mixers. And unlike current up-conversion
schemes, there is not even a crystal filter of some sort at the output of
the first mixer.

Switch to an IF in the HF range, and you immediately eliminate most image
problems. No fussing over the front end about that, and of course, you
won't have to have the front end tracking the tuning oscillator.

Remember, a whole wave of amateur transceivers and receivers went
to that sort of scheme. And unlike general coverage receivers, you
don't have to worry about any problems due to the IF being in the tuning
range, and you can think up various schemes to do the tuning since you
don't have to cover the 30MHz.

YOu can stick with the modular theme, and thus build only for the
bands you want or even build a band at a time. But instead of a whole
converter, you'd have the preselector circuitry (and maybe an RF stage) and
the variable oscillator for each band. Or build a good receiver up till
the input of the mixer, and then figure out what comes next.

IN the sixties, that wave of single conversion to IFs in the MHz range
used various schemes to deal with the local oscillator. Obviously some
bands needed a frequency range that could easily be supplied by a variable
oscillator without drift (and some of the rigs took that to the extreme
and used the variable oscillator directly on 10metres). The problem
with bandswitching the oscillator would of course be the issue of
getting it to tune only 500KHz or so on each band (and any stability
issues caused by the switching of the LC circuits).

Other rigs used pre-mixing, so the variable oscillator would always
tune a fixed range, but it would be converted to the needed frequency
with a mixer and crystal oscillator. One does have to watch out
for spurs on the output, but it gets the extra mixer out of the signal
path, and given a relative handful of 500KHz ham bands in the shortwave
region, the cost of the crystals wasn't out of range (though maybe
today..).

Then later, some rigs used PLLs. I can't remember if the Signal One
used one, but certainly in the seventies they came along. Same basic
idea as the premixer, but the PLL was the filter so the VCO directly
fed the receiver's first mixer.

Rigs like the TS830S used a PLL for that same purpose, though they
came up with a pretty fancy scheme to limit the number of crystals
needed.

One of the things about receiver design is that the trends have
often reflected limitations of the times. There may be a good
reasons for doing things a certain way (such as adding a third
conversion to a receiver so the BFO is on a different frequency
from the one where the main gain is), but it may also mean
they couldn't do anything better at the time.

Michael VE2BVW

Ideal ham receiver
 

Then later, some rigs used PLLs. I can't remember if the Signal One
used one, but certainly in the seventies they came along. Same basic
idea as the premixer, but the PLL was the filter so the VCO directly
fed the receiver's first mixer.

Michael VE2BVW


Well the CX-7 didn't use a PLL, but the CX-11 did. It was however only for
generating a comb frequency to be used with premixing. The analog PTO's
still tuned 3.1 to 4.1 MHz.

The main problem with up conversion is the hit you take on oscillator phase
noise. These days, with the advent of the "H" mode mixer, oscillator phase
noise and birdies are THE limiting factor in receiver compromise.

W4ZCB

Ideal ham receiver
 

Harold E. Johnson wrote:
Then later, some rigs used PLLs. I can't remember if the Signal One
used one, but certainly in the seventies they came along. Same basic
idea as the premixer, but the PLL was the filter so the VCO directly
fed the receiver's first mixer.

Michael VE2BVW


Well the CX-7 didn't use a PLL, but the CX-11 did. It was however only for
generating a comb frequency to be used with premixing. The analog PTO's
still tuned 3.1 to 4.1 MHz.

The main problem with up conversion is the hit you take on oscillator phase
noise. These days, with the advent of the "H" mode mixer, oscillator phase
noise and birdies are THE limiting factor in receiver compromise.

W4ZCB


I've heard that DDS units do NOT have the phase noise problem that
conventional oscillators do. DDS does generate spurs, but if you can
find a DDS that will allow for a clock rate many times the desired
output frequency the spurs a far out of band. The Analog devices AD9954
family of DDS chips have a max clock rate of 400 mhz. If you do NOT use
the on board PLL multiplier and clock it externally from a good low
noise clock, you can overclock these chips to as much as 600 mhz!
So if you up convert to 70mhz you'd need a 100 mhz local oscillator at
10 meters. Thats 1/4 the clock (or 1/6 if over clocked).
With a 45 mhz first IF even better.

BTW I had an idea for a rig up converting to 6 meters as the first IF.
This would be dual conversion on the HF bands, though a crystal filter
at 6 meters for a fixed first IF would not be impossible here.

Ideal ham receiver
 

Ideal ham receiver
 

"Tim Shoppa" ) writes:

1. Don't even try bandswitching. Coil sets for each band. You end up
with the HBR-16, a very elegant and homebrewable receiver.

One reason there was that phase with a separate converter per band ahead
of a receiver tuning a fixed band was to avoid switching tuned circuits.
By that time, the semiconductors cost so little that it was easier to
duplicate them for each band, and then the bandswitching becomes so much
easier. No fussing about getting close to the tuned circuits, you simply
switch the "B+" and the input and/or outputs. Or, make those
converters plug in, and then no switches required at all.

I sort of alluded to this in an earlier post. Make a good receiver,
minus the variable oscillator and the front end tuning. Maybe even
put the mixer in the "plugins". Then you end up with a good receiver
that is quite flexible, because the things that you may want to play
with and may give trouble are in a separate box or plugins.

YOu can even play with things like tuneable frontends versus something
that is broadband across a ham band. Some bands might interest the
builder more than others, so they could build a really good plugin
front end for that band, and lesser front ends for other bands, or
leave off the bands they aren't interested in (but those bands
can easily be added later, unlike a bandswitched rig).

IN the sixties, there was a guy who had a whole slew of receivers
described in CQ. Virtually all of them were single bands, and he
made the point that it left off bandswitching, and of course he
could choose an IF that better matches the tuning range. Good points,
but an awful lot of duplication. Build a good receiver first,
and then play with the frontends endlessly.

Michael VE2BVW

Ideal ham receiver
 

Ideal ham receiver
 

Ideal ham receiver
 

wrote:



I don't much like the receivers I've used in contemporary tranceivers
-- the general coverage synthisized open front end ones. (I hasten to
add I haven't used any of the $4000 rigs; can't afford them). But the
ones I have used seem plagued with near-signal desensitization, front
end overload, etc., and I suppose all that comes from putting the
selectivity so far downstream.

I'm almost tempted to get an old 75s4 and shut up, but I really don't
need another room heater, so, instead, I'm thinking of building my own
receiver along the lines laid down by the late Doug DeMaw in his _QRP
Notebook_. Single conversion 160m superhet with Collins mechanical
filters in the IF and a series of down-converters for the other bands.
Anybody got any experience with the DeMaw Design?

Jim, K5YUT


There was a project to design a REALLY good sigle conversion ham radio and
here is the website:


http://www.warc.org.uk/cdg2000/The%2...ransceiver.htm


It was designed to have a fantastic dynamic range and, after seeing some
of the schematics, it has quite a few good ideas. The mixers and crystal
filters are worth studying.



One of the designers made a helical coil VCO with really good phase noise,
although the mechanical details were complex. These days, I'd want to look
into the AD9954 DDS design.

Probably still have to do something about DDS spurs, but they are fairly
low as is.

==================

So, it seems to me that there are a lot of designs for homebrew gear.
You need to look at your specific requirements to see what will suit you.

In my case, I live in a very RF HOT location, with quite a few powerful
signals. I might take the extra effort to go for maximum dynamic range.
Probably ovekill for most ham locations, but necessary for me.


Jim N6BIU






--

15:10 Pacific Time Zone
Dec 26 2006

International Time
23:10 UTC
26.12.2006

Ideal ham receiver
 

Guys, this is has been an interesting discussion. I wish I was more
knowledgeable - I would venture out building like that but I just don't
know enough.
---
I'm kind of starting over. Long story...
What would be a good receiver - or good enough to listen for VFOs, test
and build, etc.
Or better yet what should I avoid?
What about something like the Ten-Tec 1056 kit and some way to band
switch - maybe modules...
It's kind of a catch 22 - I have to have a receiver to build one (or
transmitter).

Dan KB9JLO

Ideal ham receiver
 

Well, for a reasonable starting point, the KK7B line of direct conversion
radios has a lot going for it. Good performance in a small package, and
it can be set up for most frequencies by providing an LO nad a 90' shift for
the LO in the band you want to play with.

A kit can be purchased from Kanga which has all the parts needed. They
also offer the microR2 which was in the recent QST article.

http://www.kangaus.com/micror2_receiver.htm

That particular kit is set up for 40 meters, but it'd serve as an
excellent starting point.

Kanga also has the slightly more general purpose miniR2 the does not ave
an onboard VFO, so it is easier to use on other frequencies.

The R2 series have good dynamic ranges, and make pretty good rigs. No
AGC, which takes some getting used to, but fun to use.



Jim N6BIU






--

22:25 Pacific Time Zone
Dec 26 2006

International Time
06:25 UTC
27.12.2006

Ideal ham receiver
 

bcdlr wrote:
Guys, this is has been an interesting discussion. I wish I was more
knowledgeable - I would venture out building like that but I just don't
know enough.
---
I'm kind of starting over. Long story...
What would be a good receiver - or good enough to listen for VFOs, test
and build, etc.
Or better yet what should I avoid?
What about something like the Ten-Tec 1056 kit and some way to band
switch - maybe modules...
It's kind of a catch 22 - I have to have a receiver to build one (or
transmitter).

A good receiver is important in any ham shack.

You can build state-of-the-art performance, especially
for a single-band receiver. While some have talked
about DDS/PLL VFOs, don't underestimate the perfor-
mance of a good LC VFO built with modern components,
after a bit of tweaking to nail down the temperature
compensation.

I know you have your heart set on building something,
and there have been excellent suggestions in this
thread, but it's not a crime to buy your first receiver
to give you a known-good building block for further
development.

Laura Halliday VE7LDH "That's a totally illegal,
Grid: CN89mg madcap scheme. I like it!"
ICBM: 49 16.05 N 122 56.92 W - H. Pearce

Ideal ham receiver
 

On Sat, 23 Dec 2006 11:32:04 -0500, ken scharf
wrote:

Yet another idea is a single conversion with a 9mhz IF. Since I have a
bunch of surplus 9mhz filters (they are 8 pole units with 3.2 khz
bandwidth) I was also thinking of a rig with these. True the filters
are a bit wider than common today, but if I put THREE of them in cascade
(between IF stages) they should do a good job.

A single 9 MHz IF filter unit with I/Q detection (to handle the
opposite sideband) could be an other alternative and do the rest of
the filtering in audio stages.

I would use a DDS VFO,
but would also used a tuned (not broadband) front end. I have enough
toroids and multi section variable caps in the junk box for that.

The _unloaded_ Q values shown by toroid manufacturers are not very
spectacular (in the 200-300 range at most). If you aim for a filter
loaded Q of 100, there are going to be a considerable loss (several
dB), so placing the filter before the first RF amplifier stage will
deteriorate the noise figure quite badly, which can be a bad thing on
upper HF bands.

With a preselector loaded Q in the 50-100 range would still cover an
entire WARC band without tuning and with wider bands and tunable front
end filters, a 100-500 kHz segment would still be present at the mixer
input at full amplitude. Thus, the mixer would still need to be strong
to handle all those signals in that range.

A preselector filter will most definitively help in keeping out strong
broadcast band signals (e.g. the strong 49 m BC band in Europe) from
the mixer, but it does not help much against strong amateur signals in
the same amateur band.

Paul OH3LWR

Ideal ham receiver
 

http://www.shelbrook.com/~ve7ca/Hbr200.htm

Tom

wrote in message
ups.com...
I don't much like the receivers I've used in contemporary tranceivers
-- the general coverage synthisized open front end ones. (I hasten to
add I haven't used any of the $4000 rigs; can't afford them). But the
ones I have used seem plagued with near-signal desensitization, front
end overload, etc., and I suppose all that comes from putting the
selectivity so far downstream.

I'm almost tempted to get an old 75s4 and shut up, but I really don't
need another room heater, so, instead, I'm thinking of building my own
receiver along the lines laid down by the late Doug DeMaw in his _QRP
Notebook_. Single conversion 160m superhet with Collins mechanical
filters in the IF and a series of down-converters for the other bands.
Anybody got any experience with the DeMaw Design?

Jim, K5YUT