Nuts and Volts - June 2014

+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.

Closing Notes

The output of this generator has an exceptional amplitude response of ± 0.1 dB on bands 1 through 7, and

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ITEM DESCRIPTION/PART SOURCE All resistors are 1/4W carbon film 5%. All capacitors are in microfarads. Special parts are listed below. RF DECK: IC1 MC1648 DIP MC100EL1648 SMD VD1, VD2 SMV1404-09

S1 Two-pole, eight-position wafer switch Q1 2N5179

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 *See text 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)