Homebrew projects

50 views
Skip to first unread message

Bill N2CQR MOHBR

unread,
Mar 28, 2005, 2:06:47 AM3/28/05
to
I really enjoyed the message thread sparked by the pictures of
Dale's very FB HB RX. We need more of that kind of discussion...

Here is what I've been working on in London:

40 meter DSB phone HB: UK hams recently got a doubling of their 40
meter
freq allocation and can now go up to 7.2 Mhz. I built a simple 40
meter DSB
transmitter. Solid state. VFO. Built it on a wooden cutting board
(almost
a real breadboard. Puts out about 2 watts. I run it into a heavily
modified
Ramsey kit linear. Then to a HB balanced tuner, TV lead up to the
inverted
U dipole. Works fine. Lots of fun. I use it with my Drake 2B, but
plan on
pressing into service my HB "Mate for the Mighty Midget" RX (see web
site)
(I have a 455 kc filter that I'll install eventually -- right now it
is very broad).

17 SSB phone:
I have a HB 17 meter SSB TX (see my web site). I' also use it with the
2B, but changing bands is a pain. So I'm building a dedicated RX for
17.
I have a Doug DeMaw "Barbados" reciever (someone else put the
components on
a "Circuit Boards Specialists" board. It has a 5Mhz ladder filter that
I've
broadened for pnone. I tried running the VFO at around 13 Mhz with
varactor
tuning, but it was unstable, so I'm going VXO. With 2 rocks in the 23
Mhz
range I shoud cover the phone portion of 17.

More later... Any comments or suggestions? How about following
Dale's lead and posting updates on projects?

73

Bill N2CQR M0HBR CU2JL
http://planeta.clix.pt/n2cqr

William E. Sabin

unread,
Mar 28, 2005, 7:23:26 AM3/28/05
to
The group may find the picture and very brief discussion of my homebrew gear
on QRZ.COM interesting.

Bill W0IYH


"Bill N2CQR MOHBR" <meara....@virgin.net> wrote in message
news:22f6e3ee.05032...@posting.google.com...

Dale Parfitt

unread,
Mar 28, 2005, 4:19:44 PM3/28/05
to

"Bill N2CQR MOHBR" <meara....@virgin.net> wrote in message
news:22f6e3ee.05032...@posting.google.com...
> I really enjoyed the message thread sparked by the pictures of
> Dale's very FB HB RX. We need more of that kind of discussion...
>
> Here is what I've been working on in London:
>
> Hi Bill,
I have trouble keeping up with where in the world you are, but visit your
site regularly to see what you are up to.
I would encourage others to brew their own xtal filters. uP xtals are cheap
enough today that you can buy a pile and match up what you need. W7ZOI's
articles on crystal filters takes the mystery out.
Probably the most difficult part is characterizing individual crystals so
you can plug in the numbers. I use an HP network analyzer, but Wes also
shows a test jig for doing this. Alternatively, N2PK's VNA will do an
excellent job. In the end, you can make better filters than you can buy- and
for a heck of a lot less $$.
N2PK recently sent me 2 WAV files- one recorded with the 1000MP stock 250 Hz
filter; the other with a homebrew 250 Hz filter- it took no imagination to
discern which one was cleaner.
Now, I'll go have a look at Bill W0IYH's site.

Dale W4OP


Bill N2CQR MOHBR

unread,
Mar 29, 2005, 12:39:59 AM3/29/05
to
Bill: Very FB! I especially liked the Velvet Vernier in there amidst the
digitial readouts. In my 17 meter SSB TX I used an old Simpson meter that
I had found in a radio club junk box back in 1974.

Thanks for sharing those inspirational pictures.

73 Bill N2CQR M0HBR CU2JL
http://planeta.clix.pt/n2cqr

"William E. Sabin" <w.s...@mchsi.com> wrote in message news:<2HS1e.1208$Vx1.663@attbi_s01>...

Bill N2CQR MOHBR

unread,
Mar 29, 2005, 1:03:57 AM3/29/05
to
Dale: I was faced with doing the complex analysis of the individual
crystal
parameters when I was building my first superhet (W1FB's "Barebones"
aka
"Barbados" RX). I just skipped all of the analysis and used the same
capacitor
values that Doug had used in his version. I'm sure my filter's
passband wasn't nearly as pretty as it could have been, but it
definitely produced the
desired "single signal effect." I was happy.

As I mentioned in the earlier post, I have an 80/40 meter tube type RX
(Mate
for the Mighty Midget"). It has a 455 kHz IF. This makes homebrew
filter making difficult! I tried, but crystals were hard to come by
in that freq
range. In the end, I threw in the towel and just used a 455 Khz IF
can
in lieu of the filter. Great for listening to AM! But now I want to
narrow
it down a bit, so I'm thinking about yanking out the IF can and
replacing
it with a commercial 455 kc filter from the junkbox. I need to figure
out
how to handle the impedance matching issues (input and output).

73 Bill M0HBR N2CQR CU2JL
http://planeta.clix.pt/n2cqr


"Dale Parfitt" <p...@parelectronics.com> wrote in message news:<Qx_1e.34384$oa6.2111@trnddc07>...

William E. Sabin

unread,
Mar 29, 2005, 8:32:41 AM3/29/05
to
Thanks Bill. The Velvet Vernier dial is not only a very good and beautiful
dial, it is excellent nostalgia for an era that has just about disappeared.

Dale Parfitt

unread,
Mar 29, 2005, 10:13:53 PM3/29/05
to

"Bill N2CQR MOHBR" <meara....@virgin.net> wrote in message
news:22f6e3ee.05032...@posting.google.com...
Hi Bill,

I too built the Barbados RX- don't know what happened to it though.
Have you thought of using a Murata ceramic filter in your tube RX?
They make a 4KHz unit for under $3. Not CW selectivity, but I'll bet it will
be an improvment over what you have. Typcial Zin and Zout is around 1K.
Although I have never tried it, I wonder about the possibility of brewing
your own ceramic filter from some of Murata's 455KHz ceramic resonators.
Although not the Q of a quartz crystal, it may be worthwhile. I have some
here and think I'll put one on the network analyzer and see what
characteristics I get.

Dale W4OP


Bill N2CQR MOHBR

unread,
Mar 30, 2005, 1:44:45 AM3/30/05
to
Dale: Wow, another Barbados RX builder. That was my first successful
superhet project. I now have the one I built (still on 20), and this
morning
I got another one (the one built by someone else on a factory-made
board)going on 17 with a VXO. I have a THIRD partially built Barbados
RX board. If this
keeps up, I'll soon have a BBRX museum.

As for the tube RX, I have a Toyo Communications CM filter. Markings
look good:
"445 -- 2.4 -- C" Now I have to figure out how to work this into the
existing
RX circuitry. Time to look through some mid-'60s handbooks and QSTs.

73 Bill M0HBR CU2JL N2CQR
http://planeta.clix.pt/n2cqr

Pete KE9OA

unread,
Mar 30, 2005, 6:34:33 AM3/30/05
to
The Murata filters range between 1.5k and 2k.

Pete

"Bill N2CQR MOHBR" <meara....@virgin.net> wrote in message
news:22f6e3ee.05032...@posting.google.com...

Floyd Sense

unread,
Mar 30, 2005, 7:16:00 AM3/30/05
to

Dale - regarding homebrew crystal filters - I wonder if you or any others
here have looked at Elecraft's crystal filter implementation in the K2?
It's built with discrete crystals and the bandwidth is variable over a large
range. Haven't seen that design exploited elsewhere, but don't know why.
It sure works well.

K8AC


Dale Parfitt

unread,
Mar 30, 2005, 10:04:28 AM3/30/05
to

"Bill N2CQR MOHBR" <meara....@virgin.net> wrote in message
news:22f6e3ee.05032...@posting.google.com...
> Dale: Wow, another Barbados RX builder. That was my first successful
> superhet project. I now have the one I built (still on 20), and this
> morning
> I got another one (the one built by someone else on a factory-made
> board)going on 17 with a VXO. I have a THIRD partially built Barbados
> RX board. If this
> keeps up, I'll soon have a BBRX museum.
>Hi Bill,
Did I sell you mine years ago? I seem to recall using a temp stabilized
varicap in a shielded enclosure for main tuning. It was done on a factory
board. Or was that a 6M xverter I sold?

Dale


nos...@nouce.bellatlantic.net

unread,
Mar 30, 2005, 10:38:59 AM3/30/05
to

>> Although I have never tried it, I wonder about the possibility of brewing
>> your own ceramic filter from some of Murata's 455KHz ceramic resonators.
>> Although not the Q of a quartz crystal, it may be worthwhile. I have some

I've done this with ceramic filters in tube circuits. You definatly
need to match the impedence to the tubes wich is high both for plate
and grid. What I did for that was to use a transistor IF can, filter,
IF can wired so the high impedence side was to the grids and plates.
Worked very well in a tube RX like the mighty midget.

For transistors the matching for those filters is IF can to get the
high collector impedence down to 1k range then the filter into the
base of the transistor. FETs get treated like tubes.

Allison
KB1GMX

Bill N2CQR MOHBR

unread,
Mar 31, 2005, 1:33:57 AM3/31/05
to
Dale: Wow, small world! Yea I think that is the one I'm working on. I think
you also had a DC-DC converter to bring the voltage to the varicaps up.
Very nice enclosure for the oscillator. I now have it percolating nicely
as a VXO around 23 Mhz (for the 17 meter band). Bill


"Dale Parfitt" <p...@parelectronics.com> wrote in message news:<0ez2e.30158$191.23924@trnddc02>...

Dale Parfitt

unread,
Mar 31, 2005, 9:47:09 AM3/31/05
to

"Bill N2CQR MOHBR" <meara....@virgin.net> wrote in message
news:22f6e3ee.05033...@posting.google.com...

> Dale: Wow, small world! Yea I think that is the one I'm working on. I
think
> you also had a DC-DC converter to bring the voltage to the varicaps up.
> Very nice enclosure for the oscillator. I now have it percolating nicely
> as a VXO around 23 Mhz (for the 17 meter band). Bill
>
That's it Bill! Amazing. Hopefully I placed the Dc-DC converter inside that
shielded enclosure. Glad it has a good home.
I believe that board was from A&A Engineering- seem to recall they supplied
for QST back then. That design was a very robust RX. Doug (?) had sent me
the companion TX article before release- but I never got around to building
it.
How many countries has that RX travelled to now?
Dale W4OP
Dale


Dale Parfitt

unread,
Mar 31, 2005, 7:44:47 PM3/31/05
to

"Floyd Sense" <fse...@copper.net> wrote in message
news:424a98d6$1...@newsfeed.slurp.net...
> That filter topology was, I think, first used by Ten Tec in their Scout.
From a purist standpoint there can be problems:
1. Asymmetrical skirts
2. Changing IN/OUT Z with BW
3. Shifting center freq as the BW is narrowed ( > capacity loading)
4. I am guessing here, but I would think the group delay would suffer at one
end or the other
5. Passband ripple can become excessive as BW is increased.

I looked at this approach, along with a method described in QEX last year
for dealing with the center freq shift, but came to the conclusion that I
could design a much better filter if I optimized each BW- even though it
took 3 filters.

One aspect of filters that has long been either ignored or overlooked (
even though W7ZOI details it in EMRFD) is group delay. A friend (N2PK)
recently sent me 2 WAV files of a Yaesu 1000 stock 250Hz filter and his
homebrew 250 Hz filter. The difference was remarkable- his filter was much
cleaner and crisper sounding, no ringing. Great care was taken with group
delay in his design.

Dale W4OP


Floyd Sense

unread,
Apr 1, 2005, 5:19:47 PM4/1/05
to
It would be interesting to know what was different about his filter. Do you
know?

K8AC

"Dale Parfitt" <p...@parelectronics.com> wrote in message news:3Q03e.27300
<<snip>>

Bill Meara

unread,
Apr 2, 2005, 1:57:44 AM4/2/05
to

Dale: I can't remember when it was that I bought it from you. So,
depending on the date, it could have spent time in the Dominican
Republic, Northern Virginia, the Azores Islands of Portugal, and the UK.

BTW, I always admired the neat construction of that RX. The hookup wire
used was very nice. Do you remember what kind of wire you were using.
I'd like to get some of that. Makes a big difference in the appearance
of the final product.

73 Bill N2CQR CU2JL M0HBR
http://planeta.clix.pt/n2cqr

Ted Bruce

unread,
Apr 4, 2005, 5:46:14 AM4/4/05
to

Dale & Bill,
Jim, K8IQY has the Precision VXO and Crystal test rig that uses the
PVXO as a driver for the candidate IF filter crystal under test. I'm
currently building both of those.

73,
Ted KX4OM

Ted Bruce

unread,
Apr 4, 2005, 5:54:58 AM4/4/05
to
On Mon, 28 Mar 2005 21:19:44 GMT, "Dale Parfitt"
<p...@parelectronics.com> wrote:

Dale, I checked in late on this thread; what is Bill Sabin's site URL?
I've been Googleing to beat the band, but it doesn't turn up.

Ted KX4OM

gb

unread,
Apr 4, 2005, 7:13:35 PM4/4/05
to
"Ted Bruce" <kilocycles**@**yahoo.com> wrote in message
news:b03251lma5gg5gkg5...@4ax.com...
> Ted KX4OM

K8IQY web page for this test rig
http://www.k8iqy.com/testequipment/pvxo/pvxopage.htm

w9gb


Dale Parfitt

unread,
Apr 6, 2005, 10:10:07 AM4/6/05
to

> >
> Dale, I checked in late on this thread; what is Bill Sabin's site URL?
> I've been Googleing to beat the band, but it doesn't turn up.
>
> Ted KX4OM
Hi Ted,
Plug Bill's call, N2CQR into QRZ.COM His URL is there.
Dale


Reply all
Reply to author
Forward
0 new messages