Dear forum, How do you select these xtals, I mean 2, 7, 8, 9 sort by "one leg to ground" or 1, 11, 2, 9 srt by "one leg to ground but via cap 33 pF" ? Thanks. Yours, Milarepa

Hi people, havent been this excited about homebrew since I was a kid and built my first (totally illegal) valve CW TX - thank you Ashar, do you realise what you have started? Have done the VFO and audio amp - perhaps others can post theirs as well - if anybody wants info from mine, no problems, just ask. I am using this project as a learning experience - the audio amp is built "Manhattan" style using the NJQRP pad cutter, Used "Protel Autotrax" (public domain) to do the layout for both - made up library components with pad cutter clearance and then centre punched the pads to a blank piece of board. The VFO - did the same method, but "joined the dots and filled in the earth plane with a marker pen " method - crude, but works - put the components on the copper side of the board to make it easier to troubleshoot. The VFO works, but need to figure out the correct no of turns. Being an amateur, I used the tuning cap available, the section used is approx 20-200pf. Looking forward to seeing others efforts and "borrowing" ideas. 73 de VK3BFA

Hi all My BITX20 is at an advanced stage of construction, but due to family commitments I won't have very much time to finish it off over the next few weeks. I used a modular construction style, each stage of the transceiver is constructed on a 2 x 1 inch (approx 50 x 25mm) of PCB stock in the "ugly" style with no PCB etching. The modules are mounted at right angles to the "chassis" which is also made from single-sided PCB. I have used tap washers like the original, except for the transformers which are 15 turns bifilar/trifilar on FT37-43. The VFO works fine, I'm using an old variable capacitor and I removed 20 turns from the 150 turn coil to get the frequency range right. I noticed the fine tune is rather non linear with voltage, and also much more effective at the low end of the frequency range than the top. Something to investigate further later. I'm using one of my simple 2-chip frequency counters with 8 LED binary readout of the frequency offset in 0 - 100KHz, 0.5KHz resolution. The cost of this module is just UK £2. See my counter page http://www.hanssummers.com/radio/sfreq/index.htm for details (the Mk1 is in my BITX20). I have some photographs for you but it'll take me a while to sort them out as I'm rather busy right now. Hopefully sometime next week I'll have them ready. 72/3 de Hans G0UPL http://www.HansSummers.com

guys, pete joins us on the group. he has details about substituting the tv baluns cores with FT-37 cores. he has also pointed out that the receiver gain is low. anybody else too who has experienced this problem? i did encounter it on two sets that i assembled (out of three). in one set it turned out o be a cold solder on an emitter bypass capacitor, in the other case, it turned out that i had swapped the collecot load and the base bias resistors on the audio pre-amp. - farhan ---------- Forwarded message ---------- Date: Fri, 18 Jun 2004 08:14:12 +0530 From: Ashhar Farhan <computercorp@...> To: jessystems@... Cc: farhan@... Subject: RE: BITX20 Transceiver pete, my hotmail box is choked. my other email address is farhan@.... and the mirror is on www.phonestack.com/farhan. i work at phonestack. i will cross post this mail of yours back to the group. if you are getting dx, then the receiver is probably sensitive enough. it is an unusually quite receiver design. as a result, it does give the impression that it is not sensitive enough. the acid test is to listen to the receiver without the antenna and with the antenna attached. if the noise goes up substantially, then it is sensitive enough. - farhan ______________________________________ Ashhar Farhan 71, Huda Heights, MLA Colony, Banjara Hills, Hyderabad. INDIA 500034. Phone - +91-40-23314077 ______________________________________ _________________________________________________________________ Expressions unlimited! The all new MSN Messenger! http://server1.msn.co.in/sp04/messenger/ Change the way you communicate!

Dear All I looked at Farhans site and found http://www.phonestack.com/farhan/xcvr1.html In that he says:- Substitutions The BF195 transistors can be substituted with any other HF transistor like 2N2222 etc. The 2N3866s are best not subsituted. The circuit works with slight increase in the noise figure if BF195 or equivalents are used in place of 2N3866s in the IF stages. The output power on the transmitter absolutely needs the 2N3866s. Subsituting them with other switching transistors didnt give good performance. The IRF510 should not be subsituted with any other transistor. The other IRFs, though rated higher, have higher input capacitance which makes them a bad choice for 14MHz operation. The LM380/LM386 can be subsituted with almost any other audio amplifier. Our first amplifier were Cambridge SoundWorks Sound System. If you turn down the bass, they are an excellent system for the shack. We have tried a TBA180, an LM386, an LM380 and even a glow-bug guitar amp. Feel free to experiment. However thanks for the component supplier. Dave M1DGS

Hi! Friends! It is a pleasure to see a dedicated group for Farhan design. I did make the last transciever designed by OM Farhan and also enjoyed a long chat with him on LL abt the same. BTX is certainly an architecture much overlooked in amateur radio circle. I am planning on making one BTX . My choice of components is 2SC2570 for RF preamp( very commonly used in CATV), 2N2904 or BF194 for the rest. 2N2222 for the pre driver. Options open for the driver are 2N3866, 2N2219, BFW16, 2N3053 or 2 nos 2N2222 in parallel as in Norcal NC20. I may also try experimenting with one of the 2SC switching devices. It is also possible to replace balun cores in mixers with ferrite beads, I will be trying this out too. Another idea that has just crept in to make a PSK only TRX based on the same as has been done by our friend Oleg on RuQRP. 9Mhz if and 5.068 Mhz xtal for LO. I would be obliged if some one can upload a scan of component layout as I would like to do my 2 bits on the same too. Greetings and Happy homebrewing. 73 Rahul VU3WJM

we have om wes, w7zoi on the list. we all know him like an old friend from his books and articles. this is a remarkable moment. - farhan

_________________________________________________________________ Looking for something? Cant find it anywhere? http://go.msnserver.com/IN/50756.asp Log onto baazee.com

Hello fellow constructors! What a good idea Hans to set up this group! Just to say I am logging in and I am keen and excited to start building this brilliant bit of kit! All the best. Duncan G4DFV

HI everyone, got an urge to return to homebrew,This looks a good restarter project. posted an order direct to you Hans.Thanks. Jack

i have posted some pictures of the rig that were in my mailbox. three of them are from hans, from andy. - farhan

dear pete, very good on your efforts. which crystals are you using? the Cb crysals available for 9MHz are quite cheap. i am using a PC-based AGC system with some kind of noise blanker and even squelch. it work smuch better than analog systems. i will post the program soon. can you resend the pcitures pse? guys on the group would love to see the pics. send it to me on this email of mine. i am cross posting this to the BITX group for others to know of your excellent success. - farhan

Hi All I've completed the VFO today, some pictures on the reflector. Just need to wait for Hans Components Inc before we go any further. VFO swinging from 4.25MHz to 4.4MHz - very adjustable with the trimmer. I used a fixed inductor of 22uH instead of the tap washer and 150 turns of 32swg - can't count that high. What are other people planning for inductor cores - is the general plan to proceed with tap washers or has anyone done the calcs for more conventional cores? Your comments welcome. Mark G0MGX

with the lpf in circuit. I've checked the lpf cut-off and I would expect some attenuation but not that much. I tried an irf530 which promptly overheated and destroyed itself as I increased the bias! hehe, david worry not. there are a couple of things that you ought to check. 1) cut the supply to the IRF510. then measure the RF output of the driver at 50 ohms resistors across the RIF510's gate. it should show 5 volts peak (that is 10 volts between the +ve and -ve swing). If you not are getting that much, then you have probably wired the output transformer incorrectly. they are probably in parallel to each other, or worse, the drain and the power supply are connected to the separate ends of the winding. check it carefully. 2) if you are not getting 5 volts at the 50 ohms resistor across the IRF510, then measure the output from the predriver. it should be a more than one volt peak (2 volts peak to peak on the 'scope). if either of these is a problem. check the following: a)that the collectors are showing somewhere north of 10 volts and the emitters are showing about 2 volts on both the driver and the predriver. b)if the DC voltages are alright, suspect that the AC connections are a problem. Most probably it is a mis-wired transformer. take them out of the circuit and check them carefully. i frequently make a mistake with shorting the opposite ends of the SAME wire and leaving the other wire in the pair isolated.d c) the 6.3 ohms, in my case is approximated by paralleling two 10 ohms. check that the 10 ohms IS 10 ohms and not 100 ohms. it is easy to confuse brown-black-brown with brown-black-black. above all, trace! measure the outputs at the RF fitler, pre-driver and the PA. tell us how much you get at each point. we will 'divide and conquer'. i dont know if i mentioned in the article that you should set the drain current to between 50 and 80mAs. I set it at 80mA, a bit on the higher side, but the linearity is better. - farhan

Many thanks for the advice Farhan.   I've taken the measurements you suggested and indeed it was the driver whose output was low - only about 1 volt peak. I was using BC549s throughout and although they tested ok when I changed them in the pre-driver and driver stages for 2n2369s the output from the driver went up to 4.5volts peak.   I've tried a variety of core types and none appears to be critical. I'm using a t-50-6 in the IRF510 drain - 14 bifiliar turns to get the 3uh you suggest. Know what you mean about winding these things!   The output without the lpf in circuit is 6.25watts but I need to adjust the bias for a standing current of rather more than 80ma to achieve this - although it may be that the balanced mod is not that well balanced (I haven't put in any caps yet). I'll test this and let you know. Even without the lpf the output is quite a pretty sine-wave.   Now where does this 6.3 volt resistor fit in? Am I looking at the wrong schematic? Perhaps in the driver emitters? I'll try changing the 10 ohms to 5.6 or thereabouts and see if the output goes up.   Lastly thanks for putting a unit on the rf voltages. All too often schematics either don't contain rf voltages at all or they don't specify whether they're Peak to Peak or Peak or RMS - and there's quite a difference!   I think I'll change the other 549s for 2n2369s if I have enough just to see what happens.   Good luck to everyone.   David

---------- Forwarded message ---------- Date: Sat, 19 Jun 2004 22:08:39 -0700 From: Pete Juliano <jessystems@...> To: Ashhar Farhan <farhan@...> Subject: Re: Fw: First QSO with the BITX20 Transceiver Hi Ashhar, For the crystal filter I am using 9.0 MHz computer crystals. I built a test oscillator and measured them with a frequency counter. Out of a group of 20, I found 4 that were within 50 hertz of each other. Those are the four in the radio. When I jumpered in a Commercial Filter to make a comparison, I didn't even have to touch up the carrier oscillator crystal so the HB filter has a very close center frequency to the commercial unit. The HB Filter does a nice job and is cheap --20 crystals cost me about $7 USD and within that remainder is another batch that could be used for a second filter. Attached are several photos of my version of the BITX20 including the Linear Amp, an overall view of the boards with digital display and a close up of the main circuit board. Hopefully next week I will have it all in a box. The VFO and stabilizer are as large as the mainboard. I used sockets for all of the semiconductors so I could do a little testing of various transistors and IC's The linear amp output filter has the following constants. 220PF, L1 which is 12 Turns of # 26SWG on an FT37-2 powdered iron core form (red core ~ 0.55 uhy). Then followed by a 220PF in parallel with a 330 PF (= 550 PF) followed by L2 same as L1 and then a 220 PF. The caps are ceramic on glass and rated at 100 volts. Really small caps. I used a 78L05 regulator and the bias adjust --I used what I had --a 25K ohm pot in parallel with a22K ohm resistor. Works fine. The linear amp board is 2inches X 2 inches (5CM X 5CM). You will note two relays --one at the linear amp just like the schematic --but I also had to resort to a relay at the main board as there was a RF feedback problem. The second relay solved that problem. The microphone is a low impedance --A D104 (lollipop) fitted with a Heil HC4 cartridge. I have a 25K ohm pot soldered right at mic connector and use that to set the mic gain. The last two evenings 20 meters has been hot and the RX is doing a FB job. Despite my initial comments about receiver sensitivity it is more than adequate. If I get a chance I may try my hand at an analog agc circuit. Again a very nice radio and despite its subtle simplicity --it packs a lot of peformance. I will keep you posted on my progress. 73's Pete W6JFR

the 2N2218 is a fatter type of 2N2222. you can use the 2N3866 instead. they are expensive in india. but they might be easier to find elsewhere. - farhan

i calculated 3uH on each winding. - farhan

Please could somebody explain to a non-native speaker what "tap washers" are and where to source them? I guess this must be some sort of "plastic toroid" (ab)used as a coil former. But what is its original use? Heinz, OE5EEP

Finally here's a full list of what I can order for you from Rapid Electronics http://www.rapidelectronics.co.uk. Prices are the Rapid prices, i.e. no profit for G0UPL :-( Postage is the price of a UK 1st class stamp for UK orders (£0.28). Other countries will be extra at cost. You must tell me your orders by this Wednesday at 13:00 UK time (12:00 GMT). I will order on Wednesday from Rapid, receive the components on Thursday, and send them out to you on Thursday. UK orders should receive them on Friday, ready for the weekend's homebrewing! Don't send any money yet, just tell me what you want and then wait until Wednesday when I have placed the order at Rapid: it might become slightly cheaper still if we go over other quantity pricing thresholds. You can pay me by any of the following methods: 1. Paypal (preferred) to my email address. Anyone can use a credit card to pay me this way, without needing to be a PayPal member, see http://www.paypal.com . 2. UK cheque or postal order 3. Cash: British Pounds, or if you like approximate equivalent amounts in US Dollar or Euro. Not other currencies please, I am a homebrewer not a bank, I can't handle Mauritanian Ouguiya or Azerbaijanian Manat. If you are going to pay by 2 or 3 above, then I will send you my postal address via email. Rapid do not stock 2N2218 driver transistors, nor are they at Farnell http://www.Farnell.com. However I have managed to find a different source for supply of 2N2219A which is like the 2N2218 but has better gain specification. I'm sure it will be suitable. So here's the prices and description: feel free to take all items or only those you think you need. To keep it simple, transistors will be in a set of 25 BC547B, and diodes in a set of 15 1N4148. This leaves a couple of transistors and diodes left over for later modifications! If there's anything else you need particularly then let me know. Varying the quantity is fine too, e.g. take two IRF510's so you have a spare if you are worried about frying them, or if you want to play with push-pull for higher output power. Prices are in UK pounds inclusive of VAT (sales tax). £3.58 Qty 10 of 10.000 MHz crystals, HC49 style £0.59 Qty 25 of BC547B transistors £0.70 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* £9.92 total, if you wanted everything and 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. 73 Hans G0UPL http://www.HansSummers.com