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

Jim,

I recently went through what you are now doing. Get a copy of EMRFD and read
through it.

I built up a DDS vfo that I could use from a few khz up to about 20mhz. I
put it in a well shielded enclosure to minimize spur pickup. The one I
built also has an lcd readout and keeping that in the shielded enclosure
keeps noise down in the rest of the receiver.

I then built up front end bandpass filters for just the ham bands and worked
with them till I was happy with their performance.

I then picked up surplus crystals off of ebay. Get 100 of the same kind if
you can. The hc49 units I got seem to work well. Then build up the crystal
filters you need and get them working.

I then built up an IF using a 1496 ic and the crystal filter.

Then I built up a mini-circuit sbl1 mixer and started hooking things
together. The mixer needs a good diplexer arrangement to do its best. I
spent some time getting that built up. I learned quite a bit about
interstage impedance matching. I used iron core toroid transformers to do
most of that (e.g. btwn the mixer and filter and btwn the filter and the IF
amp.

Add in a simple product detector and a *good* audio stage and you are all
set.

The receiver hears at least as well as my icom 751a. It doesn't have
passband tuning (and likely won't) or a notch filter (I have plans to add
an audio notch filter) so it isn't quite as good in a crowded situation.

But it *is* simple and easy to work on.

Oh, I almost forgot. I wound up building up an RF amplifier to enhance the
receivers sensitivity and added a switchable 20db pad to help with overload
situations. I also used a set of latch relays to control everything with a
whole bunch of pushbutton switches on the front panel. The relays were
expensive but work really well.

Anyway, I think you can build a single conversion receiver that will be
quite adequate even compared to todays equipment. Give it a try!

tim ab0wr

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

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

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

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

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

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