[minima] Re: Favorite Minima Modifications
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Wed, 18 Feb 2015 22:34:41 -0500
Hi,
I think he meant another differnt kit (not minima) to build, least I
read it
that way.
My variant...
11.2735mhz as I have a nice 8 pole 2.1 khz filter and both upper and lower
sideband carrier crystals. Its not in close proximity of ham bands so that
helps avoid a notch (still needed) that would hurt 30M or 20M. I have
several
radios for short wave listening so this is ham only. I'm using
conventional
DBMs, again I have them. IF will be CAS-B (I plan to have a minimal AGC)
and on the other side of the filter will be a pair of J310 common gate
(high threshold amp). The end signal side of the mixer will have a
2/3rds octave band pass filters (3-30mhz). that will be between the mixer
and the antenna (plus preamp, switchable attenuator) for receive and
in place for TX before the TX gain, TX will have low pass filters.
The filters were needed to make the output clean enough and avoid
out of band inputs (receive) that did cause spurs. Insertion loss was low
under 3dB and some cases 1dB.
I did a proto of highpass/lowpass filters using SMT parts and liked them
for size and low coupling between components (inductors).
If direction switching will be done with FST switches. The proto ran
well with
small sealed relays. and the ones used had better isolation. I may
stick with
relays.
The interface to the Balanced-mod/product detector will be a circuit I
worked out
years ago using the same transistor as emitter follower on tx and common
base
on receive for a good match.
Receive audio will be nothing exotic, likely all discrete. I'd like
something with
better distortion than lm386.
Other built in circuits. Tx ALC, trivial circuit but I've used it on
several radios and
its effective. Cost is 1 transistor, a diode a few caps and resistors
plus a zener
(emitter base of a 2n3904 reversed biased). Its there to avoid hitting
the power
output peaks hard and avoiding splatter. Also provides a small amount of
compression helping talk power.
RX AGC takes a fet and two transistors, few diodes and caps. Goal is to
keep
the S8-S9 and above signals and keep them from overloading the product
detector
and my ears. For weak signals it will do little to nothing. This is
far easier than
trying to keep 20 millivolt down to a 1 microvolt signals at the same
level and
is rarely needed.
Configuration will use a micro to do band switching based on tuned frequency
and other minor things like running a si570 for the LO and frequency
display.
Mode (upper/lower, CW), power on, TXing, and a simple S-meter will be done
with leds.
My goals were simple radio, low RX power drain, 5W nominal, compact for
portable use, with performance on receive on par with Elecraft K2 and TX
cleaner than commercial rigs.
NOTE: the K2 was the near top dog of the receiver specs game for many years
before everyone realized they could do better. See Sherwood engineering
web page on that. http://www.sherweng.com/table.html
Allison
On 02/18/2015 07:46 PM, farhanbox@xxxxxxxxx wrote:
>
> robert it is unfortunate that people are kitting thr minima. in fact,
> it is illegal as i have expressedly prohibited kitting until we are
> ready with design that meets spectral purity of at least -40 dbc and
> peferably -50 dbc. we are not at that point yet.
>
> this primarily due to the IF being inside the pass band. you could try
> making it to just cover upto 14 mhz. the original circuit should work.
>
> - f
>
> ------ Original message------
>
> *From: *Robert Toegel
>
> *Date: *Wed, 18 Feb 2015 23:42
>
> *To: *minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>;
>
> *Subject:*[minima] Re: Favorite Minima Modifications
>
> Haven't done anything yet. Just got a kit that somebody just started
> to build.
>
> Bob
>
> On Tue, Feb 17, 2015 at 11:17 PM, Josiah Ritchie
> <josiah.ritchie@xxxxxxxxx <mailto:josiah.ritchie@xxxxxxxxx>> wrote:
>
> What are your favorite modification to the minima and why do you
> like them? I'm playing around with it all right now and am
> thinking about what I might to do make mine my own so it made me
> curious.
>
> Thanks,
> JSR/
>
>
Other related posts:
