Modern Zwischenbasis amplifier(*) for
Mixer IF termination
c19. Moderne Zwischenbasisverstärker für ZF
see previous notes and history details
The basic low-noise, high-intercept-point
amplifier with gate-source feedback and using the
Siliconix VMP4 power FET as implemented by W4ZCB. To minimise leakage inductance, the single turn
braid must use brass end plates so the braid can be opened up and pushed into contact with the sides of the
hole in the binocular core. However, reasonable results can be obtained with just the braided with enamel
inside and no end plates. (Reference 3)
Alternative circuit with 2N5109 has IP3=17dBm on page n16
1) Zwischen-Basis amplifier with J308 2) G3SBI Radcom TT Dec 95 pp70-71
2) Zwischen-Basis cascode-amp. with J310 1) G3SBI Radcom TT May 95 pp60
3) Zwischenbasis amplifier W4ZCB and G3SBI Radcom TT Sept 96 pp70-71
4) Zwischen-Basis JFET amplifier 4) G3SBI Radcom TT Sep 98 pp 58-59
5) ZB: Transistor-Konverter für 145MHz DJ2LR UKW berichte 1/64 pp.1-3
See more similar notes found in recent Radcom and other magazines
pg n16. LA7MI highlevel mixer experiments and notes
Stein Torp, LA7MI made some calculation to find
the formula to calculate the input impedance for a known fet
(20mmho) with different
turns ratios, where (for simpler calculation) the source is tapped 1 turn from center tap, and the gate winding is varied.
He sent me a letter where he shows how to find the expression, but I haven't found all the proper symbols, so only the conclusion is shown
Leif Hansen, LA6LCA suggests using MRF134 FETs for higher order IP3, see the note below.
I am not sure it is neccessary to go into the mess using brass or copper tube for the single winding, I've just tested another transformer using coax braid instead, perhaps equal transformer, but it is an indication that it might work well.., see page n16. Core info: Philips 3122 134 90783 Ferrite grade 4A4 permeability 500. 4v per turn at 80m band gave 20°C temperature increase. 1 turn = 0.9µH, O.D.= 10.5 mm, I.D. = 6.9 mm, 19.5 Long (LA8AK)
2m RX pre-amp using MRF134. The device needs 100-150mA for low noise figure, maximum voltage 28VDC. Suggest to use a constant current circuit as shown, but only a simple circuit is shown, some optimization of input impedances is neccessary for optimum noise factor (LA6LCA).
See also the VHF notes on page d12.
LA7MI has experimented further with Zwischenbasis amplifiers and here is his DG-FET version for 10.7MHz
The 10,7MHz amplifier has 18dB gain (50 ohm). Noise factor is supposed to be 2dB. Input return loss is 20dB, it may be optimized by changing the 2700pF capacitor.
Coils on input and output are wound on Amidon T50-2 cores. Trimming is done with stretching and pushing the turns on the toroids. He has used
SMD components, didn't notice any sign of instabilities or oscillations, the 47W resistor in gate 2 is important to avoid spurious instabilities. (LA7MI Stein Torp 2003.06.03)
NOTE *) Zwischenbasis
amplifiers were first described by Cantz in Telefunken
Mitteilungen 1953. The German name is not easy to translate to