Hi Arv,

I'm thinking of building a 40m version of the BITX20. As Ashhar
mentions in one of his earlier mails, that is the band more popular
here in India.

Could you please guide me on the different stages of the circuit you
modified and the nature of changes you made?

Also, may I please have a copy of the gif file of the discreet
components AF Amplifier?

Thanks in advance.
73s,
Bharat, VU2BDX


--- In BITX20@..., arvevans@e... wrote:

Hello to the BITX20 group (this is my first posting on this forum).

Farhan and myself have exchanged a couple of off-forum emails

regarding mods to his excellent design. One interesting possibility
is replacement of the LM-386 with a discrete component AF Amplifier.
He said that he had not had the time to work up a schematic...so I
have provided one (see attached .gif file). This can allow those
without access to an LM-386 to build the unit.

Also, my layout for the BITX20 uses 10.7 MHZ IF transformers

salvaged from dead AM/FM radios ( I dislike winding toroids! ). My
construction is a BITX40 (40 Meters) and requires 55 pf across the
10.7 IFs to resonate on 7.2 MHZ. These 10.7 IF transformers might be
made to resonate on 20M if the internal capacitors were removed (
break them with a screwdriver point ) and a small variable ( 5-25pf )
used to bring them to resonance.

73's
Arv - K7HKL

On Jul 11, 2004, at 8:53 PM, bainopaul wrote:

Brasso is another cleaner that I have used in the past. Does an
excellent job!

I'd like to remind all that ScotchBrite is a relatively non-reactive abrasive matrix that works well with reasonably non-reactive chemicals. It's worth trying with Tarn-X or other "tarnish-removing" chems. I'm going to experiment with a few other commonly (globally) available chems.


I'll report what I find, unless I find something that combusts.

Jim N6OTQ

Brasso is another cleaner that I have used in the past. Does an
excellent job!




73 de Baino


--- In BITX20@..., "Bruce Raymond" <bruceraymond@s...>
wrote:

I'd like to suggest the use of a copper/silver cleaner, such as

Tarn-X. I don't know

what would be similar across the pond or in other parts of the

world. I just pour a

little bit of Tarn-X on a paper towel or rag and then wipe the

pcb. Be sure to wash

off the Tarn-X residue with water when you're done. I've heard of

people using

toilet bowl cleaners and such, but this appears to be more

benign. It does a

reasonable job, although not as good as a serious session with

steel wool. OTOH,

it's a *lot* less work ;-)

- Bruce ND8I


-----Original Message-----
From: Charles Darley [mailto:charles@d...]
Sent: Friday, July 09, 2004 2:55 PM
To: BITX20@...
Subject: RE: [BITX20] Cleaning PC Board material for your BITX

transceiver construction

Hi
Can I also suggest that where the components are to be placed

that the PCB pad is tinned and where earth connections are to be
made that area too is tinned, as it ensures a good joint and the
joint is quicker too!!

I think the sort of bush mentioned has brass wire bristles and

used for cleaning suede shoes !!

Charles G4VSZ


-----Original Message-----
From: Arv Evans [mailto:arvevans@e...]
Sent: 09 July 2004 19:00
To: bitx20@...; rlelm@a...; leatkin@e...;

bequan@m...; ciresnave@y...

Subject: [BITX20] Cleaning PC Board material for your BITX

transceiver construction

Hi

PC Board material that is stored for some time usually takes on

a layer of oxidation that hinders soldering components to its
surface. In the past I have routinely used sandpaper to remove this
oxidation and prepare the surface for my "ugly construction"
projects. Now I think I might have found a better way to prepare
the surface. I tried a small wire brush and found that it not only
removes surface oxidation, it also leaves a much more polished
surface and requires less effort. The wire brush was purchased at a
local hobby store for about $1 US, see the picture below. If you
have a small wire brush you might try it and see if it works for you.

73's
Arv
_._



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?

Thanks a million, Monty, Great job. And thanks to Arv Evans for sharing
this circuit :-)


Regards,
John

=============================================
email: k5jhf@...
photos:
files:
webpage:
callsign: K5JHF
=============================================

?

? Hi

PC Board material that is stored for some time usually takes on a layer of oxidation that hinders soldering components to its surface.? In the past I have routinely used sandpaper to remove this oxidation and prepare the surface for my "ugly construction" projects.? Now I think I might have found a better way to prepare the surface.? I tried a small wire brush and found that it not only removes surface oxidation, it also leaves a much more polished surface and requires less effort.? The wire brush was purchased at a local hobby store for about $1 US, see the picture below.? If you have a small wire brush you might try it and see if it works for you.



73's
Arv
_._

开云体育

Hi

PC Board material that is stored for some time usually takes on a layer of oxidation that hinders soldering components to its surface.? In the past I have routinely used sandpaper to remove this oxidation and prepare the surface for my "ugly construction" projects.? Now I think I might have found a better way to prepare the surface.? I tried a small wire brush and found that it not only removes surface oxidation, it also leaves a much more polished surface and requires less effort.? The wire brush was purchased at a local hobby store for about $1 US, see the picture below.? If you have a small wire brush you might try it and see if it works for you.



73's
Arv
_._

Thanks, Arv.
73s
-----
Bharat D Balsavar
VU2BDX

From: Arv Evans <arvevans@...>
Reply-To: BITX20@...
To: BITX20@...
Subject: RE: [BITX20] Toroids have legs! ;-)
Date: Thu, 08 Jul 2004 00:28:47 -0600

Bharat

The turns on that coil were sloppy because I got tired of winding them.
There are 150 turns of #42 wire on that coil. While it does work at
about the intended inductance I would probably be a bit more careful in
winding a final version of my inductors. That particular coil was wound
more for the purposes of the photograph (to show the "legs" on the coil)
than to be a final design component.

Now, to answer your question...the number of turns is more important
than the beauty of the winding. I find that for a predictable
inductance value I need to make sure the turns are equally spaced, but
for less critical construction I can usually get away with
scramble-wound coils. In the BITX20 project we are departing a bit from
typical toroid coil methods in that we are using air-core toroids
instead of the usual powdered iron or ferrite core material. This means
that:

(1) It will take over twice the number of turns than would be
required for an equivalent ferrite cored inductor.

(2) It is probably more important that the turns be evenly spaced
around nearly the full diameter (360 degrees) of the 'tap washer' former
in order to obtain the tight magnetic field that is typical of toroid
coils.

(3) Since Farhan quoted the number of turns required based on his
very neat air-core toroids, if you wish to duplicate the design exactly
you should probably make you coils look like his.

(4) I was surprised to find that the "air-core" toroids showed some
characteristics that I had previously thought were due more to the
ferrite core material than to the circular layout of the coil. This
specifically was the very light coupling I was able to get with my dip
meter. I had to use a coupling loop to obtain a good dip indication.
I think this indicates that the shape of the coil is more important than
I had thought, and that this toroidal shape probably helps to minimize
unwanted coupling between inductors, and between an inductor and other
components of the circuit.

(5) The use of "air-core" type toroids is probably a plus in this
design because ferrite material is inherently temperature unstable.
Thus an air-core coil for the VFO tuned circuit should be easier to
stabilize for frequency than one with a ferrite core material. For the
VFO inductor you should be careful to make the winding as tight as
possible (or just cover it with hot-melt glue like I did) to make sure
that there is minimal physical movement of the turns with temperature
changes or vibration.

(6) For Farhan's BITX design the use of Tap Washers as coil formers
is probably the most common method because they are usually black and
thus look like their ferrite cored cousins, even though they are
actually working as air-cored toroids (yes, the dielectric constant of
nylon or PVC is not quite the same as that of air). You can use nearly
any plastic material for the former for air-cored toroids. If you
wonder if your particular plastic is suitable for RF use, you can put a
piece of the material in the microwave oven for a minute to see if it
gets warm. If it heats up under 1 minute of microwave exposure you
should probably look for a better material.

You may notice from the pictures that I did not use "tap washers".
Instead I am using 1/4 inch long slices of 1/2 inch PVC pipe. I did
this because I had the PVC pipe available and not the tap washers, and
because it let me cut a slot in the PVC to make it easier to wind the
many turns. Passing the wire through that slot is much easier than
threading it through the hole in the core. If you use PVC instead of
Tap Washers you may have to adjust the number of turns slightly to
obtain the correct inductance value. In my case I used a dip meter and
Farhan's indicated capacitance values to determine if I had the correct
number of turns. This way I maintained the original design L/C ratio
and hopefully about the same Q factor that Farhan used.

I hope this helps. Please feel free to ask more questions. Either
myself or some of the more expert people on this forum should be glad to
help.

73's
Arv - K7HKL

On Wed, 2004-07-07 at 23:29, Bharat Balsavar wrote:

Hi,

This is indeed a good idea.

I have a question - basic becuse I'm very new to this field!

I noticed that some of the turns are closely wound while some are not.

How does this affect the performance of the inductances and are there

any

thumb rules or 'brewing' basics to have a more even winding?

TIA.

73s
-----
Bharat D Balsavar
VU2BDX

From: Arv Evans <arvevans@...>
Reply-To: BITX20@...
To: bitx20@...
Subject: [BITX20] Toroids have legs! ;-)
Date: Wed, 07 Jul 2004 12:55:40 -0600

Hi

In converting the BITX20 design for building my BITX40 transceiver I
found myself 'experimenting' with several different sets of air-core
toroid inductors. Soldering, removing, & re-soldering these into the
circuit quickly became a slight problem because the windings kept
unwinding. Here is my solution to that problem (see the photo).



Since I am using slices of PVC pipe for my toroid forms, it was easy to
push a heated wire into the PVC and use this to anchor the windings.
These short wires (actually the cut off ends of various resistors and
capacitors left over from building my BITX20) now serve as component
mounting legs for the toroids. If the wires are a bit loose in their
holes ( from my overheating them during the insertion process ), a drop
of super glue fixes the problem.

Note that in the picture there is a toroid with a capacitor in the
middle. This is an alternative to the above idea. I simply super-glued
the capacitor leads to the sides of the PVC coil former and connected

my

coil ends to the capacitor's leads.

I do not know if the same idea can be applied to 'tap washer' based
toroids. Since they are a bit smaller it might take more care in
positioning the inserted wires.

Arv - K7HKL
_._
<< ToroidsHaveLegs.gif >>

_________________________________________________________________
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开云体育

开云体育

Hi

Since Farhan's stated original intent in designing the BITX20 was to provide an inexpensive transceiver, maybe it would be appropriate to show BITX builders an inexpensive way to measure unmarked or questionable capacitors.? The following circuit came to me via Don Metzger - K8JWR, but I suspect the method has been around for quite some time.? The picture shown here is the relatively simple schematic for this tool.



Use a mains transformer that delivers a few ma. at about 15 volts RMS.? Connect a known .001 mfd capacitor at Cx and adjust the value of R1 ( for R1 I used a 250K trim pot salvaged from an old circuit card ) for an indication of 1.000 volts on your DVM.? Now you can measure capacitor values from a few pf up to 0.001 mfd by connecting them in the place of Cx.?

I used this method to "calibrate" the knob indicator on a 3X450 pf variable capacitor that I regularly use as part of my test equipment repertoire.? Now I just set the dip meter to the desired frequency, and use the variable capacitor to tune my inductor for a dip on that setting.? Once the coil is on-frequency I can read the capacitance from my calibrated variable capacitor and substitute that value of fixed capacitance into the circuit.

Part of the fun derived from building your own ham radio equipment is in devising ways to perform complex design and testing by use of relatively simple and inexpensive methods & equipment.? This idea fits into that category.

73's
Arv
_._

Before someone asks the question...No, this circuit will not measure electrolytic capacitors, but it will get you close enough for most of the small caps you will be using in designing resonant circuits for HF applications.
---------------------------------------------------------

Has anyone measured the Q of the toriods? I wondered whether it
mattered too much provided the winding details were observed.

However care has to be taken with the coating materials.
There is an interesting note by Roy Lewallen, W7EL on Mounting
Toroidal Inductors with Common Materials:-

His results show that his black sealing tape reduced the Q of his
coil by nearly 40%. Other materials were noted to have lesser effects
although some were worse than others, notably Duco cement. Duco
cement is a nitro cellulose household glue which reduced the Q by
nearly 25%.

Dave M1DGS

开云体育

Bharat

The turns on that coil were sloppy because I got tired of winding them.? There are 150 turns of #42 wire on that coil.? While it does work at about the intended inductance I would probably be a bit more careful in winding a final version of my inductors.? That particular coil was wound more for the purposes of the photograph (to show the "legs" on the coil) than to be a final design component.

Now, to answer your question...the number of turns is more important than the beauty of the winding.? I find that for a predictable inductance value I need to make sure the turns are equally spaced, but for less critical construction I can usually get away with scramble-wound coils.? In the BITX20 project we are departing a bit from typical toroid coil methods in that we are using air-core toroids instead of the usual powdered iron or ferrite core material.? This means that:

?? (1) It will take over twice the number of turns than would be required for an equivalent ferrite cored inductor.

?? (2) It is probably more important that the turns be evenly spaced around nearly the full diameter (360 degrees) of the 'tap washer' former in order to obtain the tight magnetic field that is typical of toroid coils.

?? (3) Since Farhan quoted the number of turns required based on his very neat air-core toroids, if you wish to duplicate the design exactly you should probably make you coils look like his.

?? (4) I was surprised to find that the "air-core" toroids showed some characteristics that I had previously thought were due more to the ferrite core material than to the circular layout of the coil.? This specifically was the very light coupling I was able to get with my dip meter.? I had to use a coupling loop to obtain a good dip indication.?? I think this indicates that the shape of the coil is more important than I had thought, and that this toroidal shape probably helps to minimize unwanted coupling between inductors, and between an inductor and other components of the circuit.

?? (5)? The use of "air-core" type toroids is probably a plus in this design because ferrite material is inherently temperature unstable.? Thus an air-core coil for the VFO tuned circuit should be easier to stabilize for frequency than one with a ferrite core material.? For the VFO inductor you should be careful to make the winding as tight as possible (or just cover it with hot-melt glue like I did) to make sure that there is minimal physical movement of the turns with temperature changes or vibration.

?? (6)? For Farhan's BITX design the use of Tap Washers as coil formers is probably the most common method because they are usually black and thus look like their ferrite cored cousins, even though they are actually working as air-cored toroids (yes, the dielectric constant of nylon or PVC is not quite the same as that of air).? You can use nearly any plastic material for the former for air-cored toroids.? If you wonder if your particular plastic is suitable for RF use, you can put a piece of the material in the microwave oven for a minute to see if it gets warm.? If it heats up under 1 minute of microwave exposure you should probably look for a better material.

You may notice from the pictures that I did not use "tap washers".? Instead I am using 1/4 inch long slices of 1/2 inch PVC pipe.? I did this because I had the PVC pipe available and not the tap washers, and because it let me cut a slot in the PVC to make it easier to wind the many turns.? Passing the wire through that slot is much easier than threading it through the hole in the core.? If you use PVC instead of Tap Washers you may have to adjust the number of turns slightly to obtain the correct inductance value.? In my case I used a dip meter and Farhan's indicated capacitance values to determine if I had the correct number of turns.? This way I maintained the original design L/C ratio and hopefully about? the same Q factor that Farhan used.

I hope this helps.? Please feel free to ask more questions.? Either myself or some of the more expert people on this forum should be glad to help.

73's
Arv - K7HKL

On Wed, 2004-07-07 at 23:29, Bharat Balsavar wrote:

Hi,

This is indeed a good idea.

I have a question - basic becuse I'm very new to this field!

I noticed that some of the turns are closely wound while some are not.

How does this affect the performance of the inductances and are there any thumb rules or 'brewing' basics to have a more even winding?

TIA.

73s
-----
Bharat D Balsavar
VU2BDX

From: Arv Evans <arvevans@...>
Reply-To: BITX20@...
To: bitx20@...
Subject: [BITX20] Toroids have legs! ;-)
Date: Wed, 07 Jul 2004 12:55:40 -0600

Hi

In converting the BITX20 design for building my BITX40 transceiver I
found myself 'experimenting' with several different sets of air-core
toroid inductors. Soldering, removing, & re-soldering these into the
circuit quickly became a slight problem because the windings kept
unwinding. Here is my solution to that problem (see the photo).



Since I am using slices of PVC pipe for my toroid forms, it was easy to
push a heated wire into the PVC and use this to anchor the windings.
These short wires (actually the cut off ends of various resistors and
capacitors left over from building my BITX20) now serve as component
mounting legs for the toroids. If the wires are a bit loose in their
holes ( from my overheating them during the insertion process ), a drop
of super glue fixes the problem.

Note that in the picture there is a toroid with a capacitor in the
middle. This is an alternative to the above idea. I simply super-glued
the capacitor leads to the sides of the PVC coil former and connected my
coil ends to the capacitor's leads.

I do not know if the same idea can be applied to 'tap washer' based
toroids. Since they are a bit smaller it might take more care in
positioning the inserted wires.

Arv - K7HKL
_._
<< ToroidsHaveLegs.gif >>

_________________________________________________________________
Claim your Citibank Ready Cash today. It?s fast, easy and affordable.

OK, those are cute.

And way cool, ESPECIALLY the parallel LC config that uses the cap's legs for termination and mounting.

I love this place.

Jim N6OTQ

开云体育

Hi

In converting the BITX20 design for building my BITX40 transceiver I found myself 'experimenting' with several different sets of air-core toroid inductors. Soldering, removing, & re-soldering these into the circuit quickly became a slight problem because the windings kept unwinding. Here is my solution to that problem (see the photo).



Since I am using slices of PVC pipe for my toroid forms, it was easy to push a heated wire into the PVC and use this to anchor the windings. These short wires (actually the cut off ends of various resistors and capacitors left over from building my BITX20) now serve as component mounting legs for the toroids. If the wires are a bit loose in their holes ( from my overheating them during the insertion process ), a drop of super glue fixes the problem.

Note that in the picture there is a toroid with a capacitor in the middle. This is an alternative to the above idea. I simply super-glued the capacitor leads to the sides of the PVC coil former and connected my coil ends to the capacitor's leads.

I do not know if the same idea can be applied to 'tap washer' based toroids. Since they are a bit smaller it might take more care in positioning the inserted wires.

Arv - K7HKL
_._

Hans

When working with really small wire (ie. you don't have anything
better to work with!) try twisting two or even three conductors
together and use this as one wire to wind your toroid coils. This
gives you both a stronger wire for winding, and more skin-area for a
lower coil resistance. If the wire is really small there should still
be enough room on your core former for the required number of turns.

Arv - K7HKL
_._


--- In BITX20@..., Hans Summers <Hans.Summers@t...> wrote:

Nice one Arv!

Now we're on the subject I'll share my own method and experiences in

case it

helps anyone.

I don't have available nice new spools of wire labelled 28 or 32

swg. I do

have a junk box full of all sorts of things. I had some metres of wire
removed from a defective lighting dimmer switch. I have no idea what the
gauge of this wire is, but for the purposes of this project I called

it swg

28 for the time being.

Finer wire was more of a problem. I have a number of old defective

emergency

lighting controller PCB's donated by the facilities manager at my

office.

Each contains several small transformers, which use a powdered iron core
rather than E I laminated construction. These small transformers are

easy to

break up by carefully using a pair of pliers to crush the core, and

easily

remove the wire.

I had a little trouble finding wire of suitable thickness. Some of

it was

rather thin and when I attempted to "trifilarise" it, it snapped. What I
called "28 swg" turned out to be too think to get 40 bifilar turns

on a tap

washer for the power amplifier transformer. So I had to hunt for

something

slightly thinner, but not quite as thin as the wire I found and

called "32

swg".

Another problem to be wary of is straightening the wire after

removing from

the bobbin. Doing it using your fingers will lead to a nice clean

but deep

cut. Just think about cheese cutting wire. Once I'd reminded myself

of this

painfully, I used the rubber shaft of a mains-testing screwdriver to
straighten the wire. I tied one end of the wire to a kitchen

cupboard door

handle, and wound one turn around the screwdriver shaft. You can

then pull

through to the end of the wire and it straightens it perfectly. I

mentioned

this on the GQRP list and someone mentioned soing the same thing,

using a

dowel wooden rod (a bare metal screwdriver shaft would probably

damage the

wire's enamel).

Once I had salvaged enough useful wire, I created trifilar wire by

taking

three 5-foot lengths of wire, and tying one end to the cupboard door

handle

again. The other ends were clamped in the chuck of my electric drill. By
using the drill on its slowest setting I was able to quickly wind

trifilar

wire. The tension in the wire is important. Too slack, and it twists

up into

a ball. Too tight, and the drill snaps the wire. I found the right

tension

was to pull it tight and then give back an inch or two. After each

burst of

"drilling" I counted the number of twists by holding the wire

parallel with

a ruler. Note that each turn creates two "twists" on the wire so

counting

the bumps for 8 turns per inch, you need 16 bumps per inch.

I found this method worked quite well for me after one or two failed
attempts. Arv's method would I'm sure give a lot more control over the
tension etc and be less likely to result in wire breakages. The only

thing

that would worry me is that at 8 turns per inch, for 5 feet of wire

that's

almost 500 turns which is quite a lot more effort by hand. I did

wind the

mixer transformer by hand using a screwdriver shaft at one end and

the door

handle at the other. About 1 foot of wire, 96 turns, and even that

was more

effort than I liked but maybe I'm just lazy ;-)

73 Hans G0UPL


-----Original Message-----
From: Charles Darley [mailto:charles@d...]
Sent: 06 July 2004 21:10
To: BITX20@...
Subject: RE: [BITX20] Trifilar Twister Tool


Hi All

What a great idea ... wish I had thought of it my self -- a bit more
control than using an electric drill !!

Charles G4VSZ
-----Original Message-----
From: Arv Evans [mailto:arvevans@e...]
Sent: 06 July 2004 20:09
To: bitx20@...
Subject: [BITX20] Trifilar Twister Tool


Hi

Twisting the wires together for winding trifilar inductors is made

easier

with a simple tool built for that purpose. A picture of my "Trifilar
Twister Tool" is attached to this email. A copy of the picture is also
available at BITX20/FILES/K7HKL/Trifilar Twister Tool.gif.

I made this using a 1 inch long section of plastic tube (3/8 In. OD

by 3/16

in. ID) and a stiff section of wire. You can build this using

material at

hand.

Operation involves securing the far end of your wire so that it will not
twist. Then connect the near end of your wire to the twister tool. By
holding the bushing and turning the crank handle you can control the
tension, count the turns ( turns / length = turns per unit length ), and
make a very clean looking double, triple, or quadruple wire for

winding on

toroid forms.

Arv
_._

开云体育

?

开云体育

Hi

Twisting the wires together for winding trifilar inductors is made easier with a simple tool built for that purpose.? A picture of my "Trifilar Twister Tool" is attached to this email.? A copy of the picture is also available at BITX20/FILES/K7HKL/Trifilar Twister Tool.gif.

I made this using a 1 inch long section of plastic tube (3/8 In. OD by 3/16 in. ID) and a stiff section of wire.? You can build this using material at hand.

Operation involves securing the far end of your wire so that it will not twist.? Then connect the near end of your wire to the twister tool.? By holding the bushing and turning the crank handle you can control the tension, count the turns ( turns / length = turns per unit length ), and make a very clean looking double, triple, or quadruple wire for winding on toroid forms.

Arv
_._
+