LA7MI Stein Torp writes that he has tested a mixer which was used in a
Redifon mobile transceiver in the late 60's, but using modern
components. The input transformer is a pentofilar wound type with 5x
3turns (0.25mm enam cu wire), see drawing for the type of two hole
core used in the transformers.T2 and T3 are wound with 2x 3turns 0.3mm
wire. With input on 80m and 10.7MHz IF (LO = 14.5MHz) 3rd order IP on
the input was measured to +20dB, and the strange is that output
termination is not critical at all. It is possible to terminate it
with an xtal filter and still obtain +20dBm, which is not at all
possible with a ringmodulator. Measured the 1dB compression point to
+10dBm, see http://www.noding.com/la8ak/12345/n16.htm

73
Jan-Martin
LA8AK
---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm

On Fri, 9 Jul 2004 19:10:13 +0100, John Woodgate
wrote:

I read in sci.electronics.design that J M Noeding
wrote (in ) about 'Strange
Redifon highlevel mixer (+20dBm)', on Fri, 9 Jul 2004:
the strange is that output
termination is not critical at all. It is possible to terminate it
with an xtal filter and still obtain +20dBm, which is not at all
possible with a ringmodulator.

Isn't it a double balanced bridge? Neither the signal input nor the LO
input can 'see' the output, so any termination there has no effect on
the input levels, and the source impedance at the output is pretty low.

Thanks for comments!
An the funny thing is that oscillator fed from 74HCU04 (4 of 6
inverters in paralell) with 0.1uF coupling capacitor, with 18.56MHz
xtal filter on the o/p and a lowpassfilter on the input the IP3
increases to +25dBm, and when the 180 ohm resistors are reduced to 120
ohm the IP3 increases to +30dBm. At last the supply voltage for
74HCU04 was increased to 7V and IP3 is measured to +35dBm.
It seems to be an advantage to use the LPF on the input, while it
would totally spoil the performance for a ringmodulator

Jan-Martin
LA8AK

---
J. M. Noeding, LA8AK, N-4623 Kristiansand
http://home.online.no/~la8ak/c.htm