Sweep: simple Hartley Sweeper

2011/8/9

An oscilloscope alone do very meaningful things for your experimental. but a SA or signal generator still be highly attractive. try build a SA/signal generator is ton of fun. filter or mixer is essential part for all you want to build, Oscilloscope alone done just little bit help. A Sweep Generator become the top one of building list.  

The video shown a full range tune, left is the frequncy( my EP version freq meter , 7bit/per second )

JF1OZL share his great easy built sweep generator on: http://www.intio.or.jp/jf10zl/csg.htm ,  the sch here: (more detail and improve refer to  JF1OZL's page.)

vk2zay also built it with minimal change.

http://www.vk2zay.net/article/93

i also build one. there is  MPF102 and 2N5485 in my part library, not very same as vk2zay and   JF1OZL had used. but it does work. check output on Oscilloscope, distortion wave is not meet exception, might because MPF102 is not suitable for that bias.  So i pick up a  oscillator from EMRFD, Fig 3.   but with modification: use 365pF AM air tune Capacitor, the transformer use Toroid T50-6, wind 25 turn, tap at 8 turn, replace the 2.7pF with a 4.7pF for enough couple at low frequency.   Sweep part keep same as JF1OZL, but i use  variode BB910, of course, replace 2N4416 with my MPF102.

RF oscillator must buffer, also pick up from  EMRFD, see Fig4.  get signal just from the Fig3's JFET source. 5pF  lightly couple to oscillator.

Here is the completed Manhattan board.

all  modification toward to lightly couple to LC tank and a lightly coupled buffer,  Hartley oscillator could get wide band tune range than Colpitts version, typically 4:1, my version tune from around 4Mhz up to 16Mhz, even high frequency is work well and low frequency need a little heavy couple to the tank.

Use the Sweeper: 10.7Mhz   Ceramic Filters (not properly loading the filter)

More fun with sweeper

this version sweeper built for a narrow  bandwidth filter adjustment, use a simple 555 version sawtooth  wave  generator.  if allow full range sweep, that would be useful for wider band pass filter,or high/low pass filter testing, an  feasible way is replace the TRF with a AM variode, i.e  the 1SV149. and an op-amp based versatile sawtooth circuit might help to align the center frequency and sweep width.

for more seriously, the output level is out of control, 4Mhz output level is double than 16Mhz does,  lead to un-acceptable test result for wide band sweep but a output transformer make a better result, 4Mhz 5DIV 15Mhz 4.5DIV, about 10% error .