Subject: Re: Broadcast Wharehous PLL From: broadcast Date: 1998/03/30 Message-ID: Newsgroups: alt.radio.pirate THANKS MARTIN FOR THE REVIEW AND YES POINTS TAKEN, WE WILL DISCUSS BELOW > >The unit was assembled and set up for maximum output as explained >in the instructions, which were clear and well written. No trouble >in assembly or tuning was noted, although adjustment of the doubler >coils could be a little tricky as reported by mbruce. > > >1./ As supplied, frequency could not be adjusted below 2.8kHz high > of nominal. Changing VC to 20pF got it just in spec. > >2./ Spurious: The f/2 and 3f/2 are well out of spec, typically > about-50dBc. Other spurii were very low, e.g. at 98MHz the > only prescaler generated spurii visible were at > +/- 1MHz and they were -71dBc. > >3./ Harmonics: Second and third were well out of spec. > e.g. at 98MHz second was -17dBc. > Values in output filter were checked and replaced with new ones, > (same nominal values) this improved second h. to -24dBc. > Even changing output tuning could not get better than -30dBc > by which time power output was 0.5 Watts. TO OBTAIN MUCH HIGHER RESULTS CONNECT A 6.8 PF CAPACITOR ACROSS THE OUTPUT COIL (RED). THIS WILL OBTAIN AT LEAST AN EXTRA 10-20 DB HARMONIC REJECTION. FUTURE BOARDS WILL HAVE THIS MOD. > >4./ 13.8 Volts: 87.5 1.05 Watts > 98 0.95 Watts > 108 0.78 Watts > 1 WATT IS OBTAINABLE AS STATED ACROOS THE BAND AT 15 VOLTS, 3/4 MINIMUM AT 13.8 JUST AS YOU TESTED >---------------------------------------------------------------------------- > >_Comments._ > > >This is a well produced kit, a nice small PCB very neatly laid out and >good instructions. The technology is bang up to date, resulting in a >low component count. The kit took about a week to arrive after >ordering direct from BWH. > >The figures look a bit disappointing at first sight, and certainly the >unit does not meet its published specs. On the other hand, many of the >units shortcomings will not matter in practice. > >The area of real concern is the harmonic performance, this unit is NOT >suitable for use direct to an aerial without a good external low pass >filter. In many areas of the world it would cause interference to Band >3 TV reception in the locality if it was connected to an aerial direct. >It is rather surprising that the performance in this regard is so bad, >because harmonic filters are not hard to design. Definitely an area >for improvement in the new version. > >The spurious performance is generally very good indeed, only spoilt >by the f/2 and 3f/2 spurs at about -50dBc. These can be reduced >by careful tuning on a spectrum analyser, but at -45dBc worst case >referenced to 1 Watt they should in practice, not cause any problems >if the unit is operated into an aerial direct. OUR UNIT IS THE BEST WE HAVE SEEN IN TERMS OF HALF FREQUENCY OSCILLATOR DOUBLED TO THE OUTPUT FREQUENCY. WE HAVE ACHIEVED -60/-70 DB ON THE BENCH,(MARTIN TRY A 680 OHM ON THE BASE OF THE DOUBLER) > If the unit is fed >into a tuned amplifier they will almost certainly be reduced to a >very low level by the tuned circuits. YEP, IN THE NOISE > The only area of possible >concern would be if the unit was used to drive a broad band >amplifier, in which case the output would need to be checked with >a wavemeter or spectrum analyser. > >Importantly, at no point did the unit 'take off' when tuning up >(no parasitic oscillation). This is good news for users with >limited test equipment. > >The power output is very good considering the device used, 2N4427. >There is a slight roll off at the high end of the band, but nothing >to worry about really. > >Audio performance is good, not quite good enough for technically >perfect stereo due to the frequency response but very adequate >for any use that you or I could come up with. It is very unlikely >that anything else at this price would have better performance, and >even if it did you would need an audiophile grade tuner to tell (or >measure) the difference. TO ACHIEVE TECHNICALLY PERFECT STEREO YOU NEED EITHER A VERY LONG TIME CONSTANT IN THE LOOP FILTER OF THE PLL OR A DUAL TIME CONSTANT. WE COULD HAVE IMPROVED THE BASS RESPONSE OF THE STEREO SEPERATION WITH ALONGER TIME CONSTANT BUT WOULD HAVE NEEDED TO SACRAFICE LOCKUP TIME. WE CHOOSE A MEDIUM LOCKUPTIME AS A COMPROMISE. (IF YOU WANT YOU CAN CHANGE THE 1M RESISTOR OUT OF THE PLL CHIP TO A 10M RESITOR THIS WILL ACHIEVE THE STEREO YOU ARE TALKING ABOUT,(OR NEAR ENOUGH) BUT BE PREPARED TO WAIT 2-3 MINUTES FOR THE UNIT TO LOCK. TO BE HONEST MOST PEOPLE COULD NEVER TELL THEN DIFFERENCE BY LISTENING. > >In summary, this unit can be thoroughly recommended, but with the >proviso about harmonics already mentioned (Get a low pass filter!). > OR PUT A 6.8 PF CAP ACROSS THE COIL AS MENTINED ABOVE. >I look forward to seeing the new unit (Scott, send me one to review!). > > NEXT WEEK PEOPLE. OH AND 6.8 INCLUDED......AS WELL AS THE DISPLAY ETC,ETC,ETC >Martin Spencer. >Engineers with attitude, >Brighton, England. >