+0.7V on the low end by virtue of R9 and R10 on the
control board, and - 7.0 volts on the high end of the tuning
pots by changing R3. Still can’t get everything to fit? Then
do what I did: change the artwork on the front panel labels.
When all is set and done with this part of the testing
and you have a minimum warm-up period ( 10 min), you can
now adjust the AGC voltage for each band. Start with the
lowest band first. Hopefully, you own a resistor substitution
box to connect to the S1A wiper and ground. Load the
output with a 51 ohm resistor and connect a scope at that
point. As you run through each band, adjust the resistance
for + 10 dBm ( 2,000 mV P-P) output and make sure you
tune through the band to select for the best overall flatness.
Make note of the R value for each band as you proceed.
You will probably find the same value of resistance will
work for several bands, minimizing the resistors ultimately
needed. One word of caution here: I use a Tektronix scope
with a 350 MHz - 3 dB bandwidth, but it is only perfectly flat
out to 100 MHz. Beyond that, it rolls off in typical Gaussian
fashion. However, I have had it calibrated for sine waves all
the way to 500 MHz in a 50 ohm environment. Now, I have
a look-up table so that regardless of what the scope
displays, the table tells me what the correction factor needs
to be. Most scopes will do a fair job up to 40 MHz or 50
MHz, but if you do not trust your scope beyond that point,
then use the AGC values shown in the print for band 8. At
this point, you can complete the unit and close it up.
The output of this generator has an exceptional
amplitude response of ± 0.1 dB on bands 1 through 7, and
June 2014 33
ITEM DESCRIPTION/PART SOURCE
All resistors are 1/4W carbon film 5%. All capacitors are in microfarads. Special parts are listed below.
IC1 MC1648 DIP MC100EL1648 SMD
VD1, VD2 SMV1404-09
S1 Two-pole, eight-position wafer switch
Q2, Q3 2N3904
MMIC GALI- 55
FB-1 FB43-226-RC JW Miller
FB- 2 FB43-287-RC JW Miller
R11 47K, 1/8 watt optional
R2 390 ohm, 1/8 watt optional
R10 392 ohm two watt CPF2392R00FKR36 Vishay/Dale
COILS: BOURNS OR FASTRON CONFORMAL COATED
L1 2500 µH
L2 680 µH
L3 150 µH
L4 38 µH
L5 9 µH
L6 1.8 µH
L7 0.33 µH
L8* 40 nH
CONTROL BOARD & FRONT PANEL:
IC1 TLO82 or TLO72
D1, D2, D3 1N916 or equivalent
P1 10K ALPHA RV24AF-10-40R1-B10K
P2, P3 10K ALPHA RV16AF-10-20R1-B10K
S2 ALPHA four-pole three-position wafer SR2511F-0403-19ROB-E9-N-W
C1 1.0 MFD 200V (or as low voltage as you feel safe with)
Potentiometers and switch available at Mouser.com.
POWER SUPPLY :
T1 120V:24V ct 0.25A 3FS-424 TAMURA
T2 120V:8V/8V@ 0.3A 3FS-316 TAMURA
MC100EL1648 Mouser, Digi-Key
VD1, VD2 Contact author
GALI- 55 MINI-CIRCUI TS.COM
Coils Mouser (usually $0.2-0.4 each)
Resistors Mouser Electronics
FB-1, FB- 2 Mouser Electronics
Transformers — Mouser or Digi-Key ( www.digikey.com)
Regulators — Just about anywhere
MC1648: Datasheets are easily obtained through Google.
GALI-55: Datasheets at MINI-CIRCUITS.COM.
SMV1404-09: I stock these.