[Lowfer] TAG in PSKAM10 Mode

[Johan Bodin]

Hi All,

Stewart Nelson wrote:


> If you can generate 4 times the desired LO, just use a dual
> flip-flop, as described in my previous post, to get the RF phase
> shift.  An advantage is that it is nearly independent of frequency.

Yes, that works very well. I have been using 74HC74 and 74AC74
(faster) with very good results.

A few weeks ago I decided to try Alberto di Bene's new software
radio so I built an LF front end inspired by Gerald Youngblood's
design "A Software Defined Radio for the Masses" from QEX
(available somewhere on the web as PDF).

My Input transformer has 1 : (2+2) turns ratio and the "mixer" is a
74HC4052 with both halves in parallel. The 'HC4052 has quite a
few ohms "ON resistance" so it works better in a system impedance
greater than 50 ohms. The "Tayloe capacitors" (:-) are 0.01 uF each.
The I/Q AF is amplified by two "3-op-amp" instrumentation amplifiers
with a gain of 100.

It works very well with one exception... My cheap soundcard seems
to have only one A/D converter which is sampling the two channels
with a 15-20 us time difference... The resulting phase shift destroys
the suppression of the unwanted sideband at higher audio frequencies...
The delay seems to be independent of sampling rate.

73
Johan SM6LKM