Subject: Re: Broadcast Wharehous PLL From: Martin Spencer Date: 1998/03/30 Message-ID: <351F52BF.234E@dial.pipex.com> Newsgroups: alt.radio.pirate =========================================================== Re: BWH 1 Watt PLL (NB: OLD TYPE). Hi all, I have now had the chance to put one of these units through a very thorough lab test with professional equipment, here are the results and my comments: --------------------------------------------------------------------------- _Results against published specifications_. _BWH 1 Watt PLL (Old i.e half frequency oscillator version)_. Frequency Range: 87.5 to 108 MHz OK. Step size: 100kHz OK. Frequency Stability: <+/- 1kHz VC had to be changed. See Note 1. Spurious Emissions: <-70dBc Worst measured -45dBc. See Note 2. Harmonic emissions: <-40dBc Worst measured -17 dBc. See Note 3. RF Power Output: 1W typ Worst measured @13V8 0.78W See Note 4. Power Supply: 12 - 15 V Regulated OK Audio input sens: 0dBu adjustable OK S/N ratio: -75dBu -67dBr rms 20Hz-20kHz 50uS DE -65dBr Q/PK CCIR WTD 50uS DE Audio F. Response: Flat 20Hz-100kHz 0dB @ 10Hz +0.77dB @ 25Hz +0.23dB @ 100Hz 0dB @ 1kHz <-0.05dB @ 20kHz -0.12dB @ 31.5kHz Audio Distortion <0.2% THD 0.07% ------------------------------------------------------------------------------ _Notes._ 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. 4./ 13.8 Volts: 87.5 1.05 Watts 98 0.95 Watts 108 0.78 Watts ---------------------------------------------------------------------------- _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. If the unit is fed into a tuned amplifier they will almost certainly be reduced to a very low level by the tuned circuits. 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. Frequency control was not perfect (probably due to the crystal being out of spec, necessitating the mod. mentioned earlier), but is perfectly OK for low power operation. Once modified, the unit would probably just meet its spec (of +/- 1kHz) over 0 to 40 Celcius, which is OK even for high power use. 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. In summary, this unit can be thoroughly recommended, but with the proviso about harmonics already mentioned (Get a low pass filter!). I look forward to seeing the new unit (Scott, send me one to review!). Martin Spencer. Engineers with attitude, Brighton, England.