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Hi All, Just to clarify, the Delta Washers I mentioned in the earlier post are shaped more like a standard Torroid a little bigger than a T 50 and not as big as a T68 so I guess around a T55????? A standard 1/2 inch or basin tap washer in the uk is much bigger and the hole in the centre is quite small. I did purchase some of these also to compare, Catalogue no C54012 ?1.29 + VAT for 10 same Supplier. I use a PIC LCD Capacitance and Inductance meter that I made last year to give me the values of the coils, as yet I have not made them for the BITX. As mentioned in another posting, the core for the winding can be made out of various things, ball point pen plastic etc. When I wind the coils I will give some uH values from my meter. All the best and happy constructing, de Bill G0BAK.

Hi I uploaded my BITX20 pictures into the photographs section http://photos.groups.yahoo.com/group/BITX20/lst I also re-organised in there a little, so that the photos which were at the top level are now sorted into directories by callsign. Some notes on my version: You will see the first picture has the BITX20 in the foreground and my 80/40m homebrew receiver http://www.hanssummers.com/radio/polyphase/index.htm in the background. The frequency counter of the receiver (also homebrew, see http://www.hanssummers.com/radio/sfreq/index.htm ) is hooked up to the BITX20 VFO on 4.278.16MHz. You can see the same frequency reading on the BITX20 readout, i.e. 14.2 from the dial + binary 64 + 8 + 4 + 2 + 0.5 = 14.278.5. The other picture shows 14.175MHz. I fitted an on/off switch, tx/rx switch and frequency counter on/off switch (in case the counter generates an objectionable birdie or other noise). A greed LED indicates power is on, the red LED indicates TX. I included a photo of my simple 2-chip 8 LED binary readout frequency counter that I installed in the BITX20 front panel. The details of this counter can be found at http://www.hanssummers.com/radio/sfreq/index.htm . It costs approx ?2.00 in parts. I constructed my BITX20 as a series of 15 modules. The VFO is built directly on the main chassis behind the tuning controls. The remaining modules are each built "ugly" on a 2 x 1 inch piece of PCB stock, mounted at right angles to the chassis. This method will allow me to experiment easily with variations on the different modules. If necessary I could easily move all the modules around because they are just soldered to the base board at either end of their 2-inch length. This method also provides for some "automatic" screening between each stage. All the modules except the product detector/exciter are shown in the "modules" photo subfolder. Sorry for the low resolution images of the modules. Some of the main pictures were taken on a friend's camera. if you have an old unwanted digital camera which is less old than my 640 x 480 resolution dinosaur, you know where to send it ;-) The rig is now awaiting testing and debugging but due to family commitments there may be some significant delay. 72/3 de Hans G0UPL

I've been using ugly-style construction, which has worked quite well. I've noticed a bunch of constructors have used Manhattan- style construction. Not being willing to leave well enough alone, I want to give it a try. Where do people get the pads? Or how does one make them from blank pcb material? I suspect that trying to punch them out of pcb material is a pretty slow and tedious process, so I suspect there must be a better alternative. tia, Bruce

Hi! Has anyone attempted to list all BITX20 components? I haven't found any link on Ashan's page. Here is my attempt at listing all components, except for the IRF510 PA (had no time). Please warn me off the list if corrections are needed. 73, Paolo IK1ZYW CAPACITORS 0.001u 2 0.1u 34 100p 3 10p 4 1u elec 2 2.2p 2 220p 3 22p var 6 365p var 1 47p 3 50u elec 6 560p 2 56p 1 RESISTORS 1/4W 10 9 22 1 100 13 220 14 470 2 100 lin 1 10k 3 10k lin 2 120k 2 1k 13 220k 1 2k2 1 2k2 9 4k7 3 XTAL 10MHz 5 (10) TRANSISTOR BC547 14 or 2N2222 IC LM386-N1 1 DIODES 36V zener 1 9.1V zener 1 1N4148 13 TRANSFORMERS INDUCTORS see text OTHER Microphone 1 Loudspeaker 8ohm 1

Hello, I have uploaded a photo of a two-hole "binocular" ferrite core (see G4DFV album). Ashtar, please can you tell me if this is anything like the TV balun that you have used? My core measures 13mm x 7mm x 6mm, the holes are 3mm diameter and the centres are spaced 6mm. Duncan G4DFV

for the last 48 hours, groups.yahoo.com has been blocked out by the two major bandwidth providers to india. most of my internet accounts belong to isps that in turn take their bandwidth from either of these two (i have several). this has been done as the indian govt. asked the isps to block certain a fanatic group (read 'hate') from being accessed from india. some of us are fighting this with the govt. and i hope that the access will be restored soon. until such a time, i cannot see the pictures that are being uploaded although access the emails (the emails are to and from my server located in boston). i cannot wait to see all the lovely efforts being made by everybody and it feels like being left out of the party. though a number of users have suggested using proxies to gain access to the site, i want to regain my right to free exchange of ideas and information as much as i believe the fringe hate group should. the issue has become significant to a number of us in india. - farhan

BITXers Since the tap washers, faucet washers here in the US, are mylon or similar plastic type material, it would seem that they do not contribute much to the functionality, other that to hold the wire coils in a circular shape. Also, since there is no magnetic field contribution by the nylon or plastic dore former it would seem that one could cut a small slot in the material to facilitate winding the coil without having to thread each turn through the center hole. After the coil was wound one could use hot-melt glue (or anything sticky that hardens well) to close the slot and to mount the coil to the chassis material. Has anybody tried this yet? Thanks, Arv-K7HKL _._

...in which G0UPL travels to his local hardware store to further investigate the nature of the infamous tap washers, and in particular the differences between ordinary and "delta" washers. Samples were successfully returned to my office and analysed in the photocopier next to a ruler then via the scanner ;-) Attached is a picture. For the benefit of those who don't get emails but read this on the Yahoo group website, I've put it in the G0UPL photos folder too. Note: Ruler measurements to the left of the 6 inch mark are in 16'ths, to the right are in 10'ths. Both are know as 1/2 inch tap washers but both measure more than 1/2 inch (12.7mm). As close as I can measure with my ruler: "normal" "Delta" Outside diameter: 23/32 (18mm) 19/32 (15mm) Inside hole diam: 5/32 (4mm) 3/16 (5mm) Thickness: 5/32 (4mm) 3/16 (5mm) Price: ?0.45 per 3 ?0.45 per 2 72/3 de Hans G0UPL http://www.HansSummers.com

Sam & other BITXers Your measurements explain my results then. Instead of tap/faucet washers I used 1/4 inch slices cut from "1/2 inch" PVC pipe (the schedule-40 or medium-thick-wall type). These measure about 13/16" OD and 5/8" ID. In my BITX20 I followed Farhan's instructions regarding the nunber of turns and my coils came out nearly perfect for inductance value. I just wound a second set of coils using the PVC material and facilitated the winding process by cutting a slot in the plastic former. This means I did not have to thread the wire through the core 150 times. These new coils check out on the dip meter as also being on-the-money for inductance. It is interesting that these "air-core" toroids exhibit some of the same characteristics as ferrite cored units. My dip meter does not get a strong coupling to the coil itself unless I add a coupling loop through the core. I thought that phenomena was due to ferrite channeling the magnetic field, but maybe the shape of the coil has more influence than I thought. Arv _._

Hi I have just posted a block diagram of the BITX - I hope I have correctly identified all the section of the main schematic diagram. Let me know of any errors. This will be used as part of a teaching aid to Amateur Radio Students in UK. Charles

Hi I was wondering how to make a pad for the chip then thought use a piece of PCB with a cut through the copper in the centre and then additional cross cuts of the copper to make the lands for the holder. By bending out the legs of the holder they can be soldered to the pad. Chip Pad Photo added to my album. Charles G4VSZ

Hi all Looking for some help here. Testing the RX today, AF amp clearly OK, the simple tests in the text work out fine i.e. Touch base Q4 static, Q3 more static, Q2 less static. Trimmers with L1,2 & 3 do little or nothing, but the trimmer in the T3 mixer has a huge effect on noise out of the speaker. At either end of the travel very loud. It looks like there is no RF coming in. I have re-wound the two mixers with no change, I'm wondering about the coils. Here's what I have: L1,2,3 22 turns 24 SWG on T-50-6 T1, T3 13 turns triffiliar 28 SWG on FT37-43 Any thoughts? Mark Jones (G0MGX) 07971 091767

Hi fellow builders, posting this link for information http://www.wia.org.au/armag/2002/AR_Sept02_Digital_Freq_Display.pdf - its a digital frequency readout using a PIC micro with user definable IF offset - might be of use to the group, and I readily admit its outside Ashan's original inexpensive transceiver concept - it would probably cost more to build than the BITx20 itself! Still, I think its an elegant solution, so let me know what you think. Its .PDF, approx 162K in size 73 de VK3BFA Andrew

BITX'ers, DEADLINE: 12:00 UTC THURSDAY 01-JUL-04 (TOMORROW!) Paolo, Farhan and myself are investigating the possibility of a complete kit of all parts for the project, including resistors, capacitors, variable resistors, etc along with the previous semiconductors + crystals pack. This will probably take a while to organise. In the interim, I have received a request from Charles G4VSZ for 4 component packs for himself and his club. I also have an outstanding request from Jim N6OTQ. So this week I will run another round of component sourcing. The components come mostly from Rapid Electronics because their prices are excellent. The LM386 comes from Farnell, because then I can be sure that it is the LM386N-1 variant, which is uncertain from Rapid. The 2N2219 comes from Viewcom (http://www.viewcom.force9.co.uk/index.htm) and incurs some postage fees which I have to add to their transistor price. The price is the price of the components, no profit for G0UPL :-( If more people order, the price will decrease slightly. Last time with 9 orders, it was ?8.19 + ?0.28 postage. At the present time with 5 orders, the prices are: ?3.29 Qty 10 of 10.000 MHz crystals, HC49 style ?0.59 Qty 25 of BC547B transistors ?0.75 2N2219A driver transistor ?1.53 IRF510 MOSFET ?0.19 Qty 15 of 1N4148 diodes ?0.07 36V Zener diode ?0.05 9.1V Zener diode ?0.05 5.6V Zener diode ?0.29 LM386N-1 Audio Amp IC (correct variety) ?1.88 Qty 5 of 2-22pF trimmer capacitor ?0.71 Miniature tuning capacitor* ?9.68 total including ?0.28 UK postage. * NOTE: The tuning capacitor is one of the miniature kind as used in portable radios. Size is 20.2 x 20.2 x 10.8mm. Control shaft is 6.6mm diameter tapped with 2.6mm thread. Panel mounting is via twwo 2.6mm tapped screws next to the control shaft. Capacitance: AM section 3.0 - 141.6pF, Oscillator section 4.0 - 59.2pF. So in parallel you'd have 200pF which is less than Farhan's design for 350pF. It might therefore be necessary to alter the VFO coil to get the required tuning range. Feel free to order extras of any item for spares, or exclude things you don't want. Any more orders? 73 Hans G0UPL http://www.HansSummers.com

the shape is easy to figure out if you already know the crystal parameters. the crystal parameters are easier to measure now thanks to the G3UUR method. i have outlined it at http://www.phonestack.com/farhan/xcvr1.html. the essential idea is that a crystal filter looks like a capacitor and an inductor in series (these are called motional capacitance and motional inductance respectively). in addition to these, between the leads of the crystal you will also be able measure a parallel capacitance. using the G3UUR method, you put each of the crystals into the oscillator and measure its frequency. then you solder a 22pf or a 33pf in series with the crystal and measure the frequency shift. the shift gives you a good approximation of the motional capacitance and given the capacitance it is trivial to calculate the inductance (given that we know the crystal's frequency). the parallel capacitance is also approximated and the crystal is completely modelled. once you know the crystal parameters, you can spend a weekend understanding the butterworth filter design. or you can use the cookbook method in EMRFD like I did, or just use w7zoi program that comes with his other book Introduction to RF Design. using the my motional parameters, w7zoi did run it through his program GPLA.exe and i have just uploaded the results to the pictures folder. i am including his comments that go with the picture below: <snip> The first file, ashhar01, part A, shows the filter I designed with your motional L of 11.95 mH. I designed for 2200 Hz bandwidth and a Butterworth response. Then the filter at part B is a more practical version of the same thing. It is much like the filter that you ended up building. My simulations suggest that is really is worthwhile to add the tuning capacitors at the ends though, for it produces a much smoother, ripple free response. The first analysis I did used equal terminations of 200 Ohms (perhaps 220) at each end and the response was of course text book. But the question remained -- what would the response be if the filter was terminated in other resistances. The file ashhar02 shows what you get with a 50 Ohm source and a 200 Ohm load. This is still pretty good. The response is not nearly so good with 100 Ohms per side, which is about the characteristic Z0 of your amplifiers. </snip> - farhan

Hello, I just measured the resonance frequency of ten 10 MHz crystals. I found a set of four within 30 Hz and another set of four within 45 Hz. How does this compare to other peoples results? Did somebody already plot the passband shape of a resulting 4 crystal filter? 73 Heinz, OE5EEP

Hi, I build some parts of the transceiver and tested every part individualy. The LF parts works fine (a pitty the schematic is not corrected with the voltage/output of the lm386). If I add a sinus LF wave to the microphone terminal, the shape looks simular on the colector. However, as soon as I connect the coil of the balans mixer to it, it becomes a-symetrical (one side is going to be clipped). If I put a lot of LF signal in it (looks heavily distorted, then I get a maximum output(after the attenuater) of about 0.2 mw. (in 50 ohm). After reducing the LF signal to a point it looks normal, the output power is very very less.... Did anyone look at the osciloscoop the way I did? Anyone measured the output? The distortion I can imagine can be caused by one of the diodes, but such low output at that moment? After the next amp (before the x-tal filter, the maximum output is about 1 mw (in 50 ohm). The reason is that I measure in 50 ohm is that the load is in the mw. meter. Thanks in advance for your comments, Chris PA3CRX

The order for the 2nd round of components is now in. With any luck, they arrive tomorrow and I despatch them to you tomorrow. Due to a shortage of 2N2219 at Viewcom I ordered the real 2N2218 from Mode Components. Slightly cheaper too :-) Just like last time, I have ordered two extra sets of components, comprising all semiconductors, ten 10MHz crystals, trimmer capacitors and a 200pF tuning capacitor. If anyone wants one of these two spare sets, the price is exactly ?8, plus ?0.28 UK postage (or whatever the postage for 50g to your country is, if you are outside the UK). 72/3 Hans G0UPL http://www.HansSummers.com

BITXers There are several alternative ways to build various parts of the BITX design. For my BITX40 I chose a PTO type oscillator for the VFO. This uses a layout similar to that done by Jom - WA6OTP <www.wa6otp.com&#92;pto.htm> for the mechanical construction, but is a BJT based Clapp oscillator circuit with emitter-follower VFO buffer. A 32 tpi (turns per inch) brass screw is threaded into a coil of #28 wound on a soda straw and covered in hot-melt glue. The present tuning range is about +350 KHz for my version. This covers all of 40 Meters (7.0 - 7.3 MHz) in 28 turns of the knob. I am still tweeking this to try for 10 KHz per turn, but that is not quite working yet. A picture has been posted (see PHOTOS in the BITX20 forum pages under K7HKL) to show the mechanical design. A schematic has not yet been finalized because the oscillator is prototype and still being modified for tuning range and temperature stability. K7HKL

Ashtar, I have followed the link to your site:- www.phonestack.com/farhan and the schematic around the LM386 still looks the same as before. Duncan G4DFV