From ianls@patrol.i-way.co.uk Sat Jan 31 07:07:39 1998 Received: from ns1.qsl.net (root@NS1.qsl.net [209.60.242.81]) by oucsace.cs.ohiou.edu (8.8.5/8.8.5) with ESMTP id HAA06938 for ; Sat, 31 Jan 1998 07:07:38 -0500 (EST) Received: from harvest.i-way.co.uk (harvest.i-way.co.uk [194.129.192.12]) by ns1.qsl.net (8.7.6/8.7.3) with ESMTP id HAA31458 for ; Sat, 31 Jan 1998 07:08:01 -0500 Received: from sparks.i-way.co.uk (190-dynamic-reading.i-way.co.uk [194.129.181.190]) by harvest.i-way.co.uk (8.8.5/8.8.5) with SMTP id MAA31238 for ; Sat, 31 Jan 1998 12:10:37 GMT Message-ID: <001e01bd2e40$8a1ec960$beb581c2@sparks.i-way.co.uk> From: "Ian Liston-Smith" To: Subject: More HW-9 mods Date: Sat, 31 Jan 1998 12:04:35 -0000 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 4.72.2106.4 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2106.4 Status: RO Eric, Thanks for the message re the HW-9. I have quite a lot of mods for the rig, many appear on your site - some look like too much bother though! It never ceases to amaze me why Heath didn't spend a little longer at the design stage to make their kits considerably better, particularly as some of the mods are trivial, but make significant improvements and would have enhanced their reputation. Perhaps it was just lack of competition... Some circuits in some of their kits are so poorly designed it make you wonder what they were playing at! Is it true that all their documentation and spares going back years were DUMPED when they got out of the amateur radio business? Or is this just a ham radio version of an 'urban myth'?! Anyway, the mods I've done to mine:- 1) To improve rx overload/crossmod performance, particularly at night on 40m in Europe: Put 100uH choke across R243. This greatly increases the current through the switching diodes D404, D403 etc. Keeping R243 in place reduces the Q in case of any possible resonances. These diodes originally only had about 2 mA to switch them on. Putting normal silicon diodes in the receive signal path is just asking for trouble, especially if they are not fully conducting. The apparent poor selectivity reported by many users of the HW-9 is probably nothing more than the 'phantom signals' generated in these insufficiently biased switching diodes. This mod also renders the addition of any input attenuator unnecessary - even in Europe. This mod was my design and published in Sprat, the G-QRP Club magazine, no 72, Autumn 1992. 2) To prevent instability on 28 MHz: Put ferrite beads between T402/L426 and the bases of the PA transistors, (and R409 and R415, though I found these unnecessary). An extra turn through the beads may be required if instability also occurs on 24 or 21 MHz bands. This does not significantly reduce the RF o/p on any band. The mod comes from LX1BK, and was published in Sprat no 62, Spring 1990. 3) Diode in base of Q103 to keep frequency constant during power adjustment. QEX October 1990. 4) Adding transistor etc. to pin 6 of U301 for better tx/rx switching. QEX October 1990. 5) Correcting audio filtering component wiring around U304B and addition of 10k resistor pin 14 of U304 to earth. QEX October 1990. (This mod appears to have cured the instability at low volume when the narrow audio filter is switched in.) 6) Improved de-coupling around U302 for better AGC stability. QEX October 1990. 7) Added 47 nF between R348 and R351 to earth and removed C338 for better audio o/p in the 'WIDE' position. (My mod/QEX October 1990) 8) To improve 9v regulation I have added 1k resistor from 9v output of U402 to top of D409. This ensures that the diode is properly 'pulled up'. (My mod.) 9) The reverse polarity of C336 has been corrected in the PCB in later versions. I apologise for what has turned into a rather rambling email, but at least it has enabled me to catalogue the mods and their sources for my own use! I hope at least the first two are useful to you for your HW-9 mod lists. If you have not yet discovered it, Q403 (417-865) is listed in my HW-9 handbook as MPSA55. 72, Ian Liston-Smith ianls@patrol.i-way.co.uk