[AMRadio] RE: Receiver update.

[Brett Gazdzinski]

Hello all AM,ers.

I got the electrical design and building parts done on the homebrew
receiver today, that just leaves the front panel to do.

The receiver works very well indeed.
I ordered a Kiwa filter module, and received it in two days
along with nice hand drawn diagrams on how to incorporate it
in various tube receiver setups.

These things are very nice...three ceramic filters
and an input and output amp.
They come with pig tail cables that you patch into
points on the IF strip.
It runs off 4.5 to 36 volts, has zero loss
(as long as you re-tune the IF transformers)
and they work well indeed.
I got the 5.5 KHz filter, and tried it in various spots in the IF.
Its best to put it at the mixer output, otherwise, strong signals
out of the filter pass band, but in the IF pass band run amuck
and cause all sorts of overloading.
I did not notice this while listening on 40 meters, but
80 meters turned into a distorted mess!
Moving the filter to the mixer output solved this problem.

These filters can take an old boat anchor receiver and turn it into
a nicely selective receiver.
5.5 KHz seems a good bandwidth to pick, especially if you have
less than perfect hearing and cant hear the real high stuff anymore.

The RF amp gain control works great, the IF gain control took
some playing with, otherwise the scope output got distorted.

I did the muting circuit with a small relay that opens up the last IF
amp B+ feed.
Its run off 7 volts of rectified and filtered filament power,
that also does the Kiwa filter.

Tuning rate is nice, fidelity seems very good, it seems very stable
in frequency and all other respects.

I compared it to the r390A over and over, and to me, it seems
like the homebrew works as good or better under most conditions.
The homebrew only does 80 and 40 meters, and they are easy
frequencies to get working well without a lot of special
design.
The filter really made a big improvement in the way the 
receiver works.

Now its onto drilling holes in the front panel, paint, labeling, etc.

While its been a LOT of cut and try, building a receiver
that works as good as what you are likely using is not
hard or impossible as long as you don't want lots of
bands or real high frequencies.

Brett
N2DTS