From owner-qrp-l@lehigh.edu Thu Oct 9 15:49:29 1997 Received: from fidoii.CC.lehigh.EDU (fidoii.CC.lehigh.EDU [128.180.1.4]) by oucsace.cs.ohiou.edu (8.8.5/8.8.5) with ESMTP id PAA05003 for ; Thu, 9 Oct 1997 15:49:28 -0400 (EDT) Received: from Lehigh.EDU ([127.0.0.1]) by fidoii.cc.Lehigh.EDU with SMTP id <35130-71768>; Thu, 9 Oct 1997 15:48:52 -0400 Received: from nss2.CC.Lehigh.EDU ([128.180.1.26]) by fidoii.cc.Lehigh.EDU with ESMTP id <35111-33370>; Thu, 9 Oct 1997 15:43:19 -0400 Received: from server1.maxwell.com (server1b.maxwell.com [199.120.55.3]) by nss2.CC.Lehigh.EDU (8.8.5/8.8.5) with ESMTP id PAA74310 for ; Thu, 9 Oct 1997 15:42:00 -0400 Received: from inferno.scubed.com (inferno.scubed.com [192.31.66.42]) by server1.maxwell.com (8.8.7/8.7.2) with SMTP id MAA08737 for ; Thu, 9 Oct 1997 12:41:48 -0700 (PDT) Received: from [192.31.66.158] by inferno.scubed.com (S3.4/s3-sgi-5) id TAA20749; Thu, 9 Oct 1997 19:36:02 GMT Message-Id: Date: Thu, 9 Oct 1997 13:42:20 -0600 Reply-To: ji3m@maxwell.com Sender: owner-qrp-l@lehigh.edu Precedence: bulk From: ji3m@maxwell.com (James R. Duffey) To: "Low Power Amateur Radio Discussion" Subject: Performance of Big $$$$ Rigs and Simple QRP Rigs (Long and Opinionated) Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" X-Sender: ji3m@192.31.66.42 X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN Status: RO I read with some interest the thread about allowing the big bucks Bells and Whistles rigs to compete with the QRP rigs in QRP contests. I am particularly interested by comments to the effect that those who use the bells and whistles rigs are at some great advantage and should not be allowed to compete with ""pure QRP" rigs such as the NC40, OHR100, SWLs and so forth. Note - I use a Kenwood TS850SAT as my primary QRP rig so you should exercise some caution in evaluating my comments. I think that the basic performance of a bells and whistles rig is an advantage, but only if the operator is experienced enough to use it. The electrical advantage is probably not nearly as great as one would think. For my talk at Ft. Tuthill last summer I did some performance comparison of simple receivers used for QRP. I also did some musing on why the performance of inexpensive simple QRP receivers plays so well against that of commercial rigs. Many people who listen to the simple receivers used in QRP rigs are amazed by their performance on CW and usually compare them favorably to their commercial rig. Given the relatively great cost differential I find this somewhat amazing. After some consideration I conclude that this is due to several issues; 1. Better RF front end filtering. Most QRP receivers have two stage bandpass filters in addition to a low pass filter, offering very good out of band rejection of unwanted signals. Many commercial rigs use only half octave low pass filters, or bandpass filters only on critical bands such as 40M. This wide input bandpass can degrade the receiver's 2nd order intermodulation performance. 2. The IF filtering is usually narrow. Most commercial rigs are sold without CW filters, while most simple rigs have good narrow IF filtering. When supplied the commercial CW filters can have poor shape factor and high insertion loss. There are second order effects here as well, many commercial rigs use filters that have substantial loss and do not compensate for this in the IF gain which is usually set up for SSB. Filter blowby can be an issue as well, as is proper filter termination, all of which are usually handled better in QRP receivers. 3. Most simple QRP receivers use multipole narrow audio filtering to supplement the IF filtering. In commercial rigs the audio filtering is often set up for SSB or missing altogether. 4. The simple rigs handle AGC better. In simple QRP rigs it is either missing (best), can be turned off, or has time constants tailored explicitly for CW. 5. The gain is better partitioned between stages in simple QRP receivers. High gain is usually accompanied by narrow selectivity, as it should be. This can be a problem in commercial rigs where the first stage usually has a wide bandwidth to accommodate FM and a reasonable amount of gain to get low noise on 10M. Well designed QRP rigs accommodate the shortfalls of the components better than do commerical rigs. Examples include the use of a potentiometer at the input to limit signal levels in the SWL series, and the use of a post filter to the MC1350 IF to reduce wide band noise generated in the IF in the Sierra. 6. Low noise oscillators are usually used in simple QRP receivers rather than the synthesized oscillators and their often high phase noise used in commercial DC to Daylight rigs. This improves weak signal reception in the presence of strong signals. 7. The audio stages of simple QRP rigs are often based on low noise "audiophile" quality devices such as the NE5532, OP275 or LMC662. The audio stages of commercial rigs in comparison often are noisy and accompanied by relatively high distortion. If the LM386 output stage is rolled off to get rid of the hiss a low noise low distortion audio stage for headphone CW is easily realized in simple rigs. Despite the low intercept point of the 602, the performance of simple QRP rigs based on the NE602/(MC1350)/NE602 chip set is surprisingly good. Using two tone dynamic range, blocking dynamic range and sensitivity as criteria, they meet the DeMaw/Hayward criteria for casual operating and approach the criteria for DXing/Contesting. They equal the performance of many rigs built in the early 80s, and far surpass the performance of the rigs that made Kenwood and Yaesu commonplace in Hamdom; the FT101 and TS520. The QRP rigs with diode ring mixers in the front end and good low noise oscillators, such as the Hands rig and some OHR models, meet the DeMaw/Hayward criteria for DXing/Contesting, and can hold their own for CW use against many contemporary commercial rigs. There are classic receivers that perform well against even today's best receivers; the Collins R390A, 75A4 and 75S receivers, the Drake R4 series, and National HROs are among the best commercial ham receivers ever made. These are tube models; as manufacturers straightened out solid state design in the early 80s such newer classic performers were produced to include the Kenwood TS930, Icom 730 and 735, and Ten Tec Corsair. Several manufacturers in the early to mid 90s produced rigs with excellent receivers, arguably some of the best performing ever made for Ham use, including the Kenwood TS850s, the Icom 765, the Ten Tec Omni VI, and the Yaesu FT1000(and its variants). The recent infatuation of Ham manufacturers with DSP has resulted in a new crop of rigs that tend to skimp on the IF filtering with the hopes that filtering can be made up by the DSP at a lower IF frequency (it can't without compromising strong signal performance). For CW digital signal processing does not appear to be a significant advantage over switched capacitor filtering where band pass and low pass filters with 12 or 16 poles can be made easily from a couple of chips for $10-$20. I have toyed with an idea for a high performance low cost QRP transceiver for home use that unfortunately has not gone past the conceptual stage. Perhaps someone on the list can implement it before I can. Both the 75S series and R4 receivers had local oscillator outputs on the back. It would be straightforward to take this output and mix it with the proper crystal(s), perhaps with a 602, buffer the output and use it to drive a final to 5 W or so. Add some simple TR switching and you have a CW transceiver with a high quality receiver. The early 75S receivers and R4s go for $200 to $300 or less when found at hamfests, so this should be a relatively inexpensive project. On to Bells and Whistles. In an exercise to determine which features I would want in a QRP transceiver I have tracked my use of the bells and whistles when I use my TS850SAT. This is an useful exercise that I recommend to anyone. I use the following all the time and would be lost without them; 1. Built in keyer with memory (although I wish it were easier to switch between a keyer and straight key) 2. Adjustable bandwidth (the independent low and high cuts are useful, though not essential) 3. An AGC off position 4. Automatic antenna tuner (although it should be in line for receive) 5. Built in SWR meter 6. RIT and XIT (I use both. They are very useful for Fox Hunts. There are good reasons why X is used to abbreviate Transmit rather than T) 7. Dual VFOs 8. Scratch pad memory (this is particularly useful during contests and Fox hunts) 9. Noise blanker (better on some bands and types of noise than on others) 10. Variable front end gain (AIP or RF attenuator) 11. Scanning memories (useful for finding satellite activity) With the exception of 8 and 11 all of these can and have been implemented in simple QRP rigs. In some cases, such as 1 and 4 they probably can be implemented better than in my 850. The resulting rig is probably not simple, but then that is the trade one makes. It can all be implemented in a straight forward manner. Well I am not sure where all this rambling has taken us, but I have tried to make the point that the big rigs with all the bells and whistles do not have that much advantage over the simpler rigs. There are contests that give bonus points for homebrew and kit rigs. That is the way it should be, but the users of simple rigs are not necessarily at a disadvantage in the Fox Hunt. Thanks for taking the time to read this far. I hope it has not been a waste of your time. - Duffey KK6MC/5 James R Duffey KK6MC/5 DM65 30 Casa Loma Road Cedar Crest, NM 87008