[minima] Re: A (temporary) solution to my mixer problems
- From: "Joe Rocci" <joe@xxxxxxxxxx>
- To: <minima@xxxxxxxxxxxxx>
- Date: Thu, 23 Oct 2014 15:51:04 -0400
I don't understand.
If the Si570 delivers +14.47 dbm into 50 ohms and you want ~7 dbm, why not just
build a 7db pad...the resistor is redundant in this case.
Also keep in mind that the Si570 output level varies with frequency, so check
it over the whole expected range before selecting a pad value.
----- Original Message -----
From: Wayne
To: minima@xxxxxxxxxxxxx
Sent: Thursday, October 23, 2014 3:11 PM
Subject: [minima] Re: A (temporary) solution to my mixer problems
Thomas,
just as follow-up to yesterday, since the 39 Ohm resistor in series dropped
my Si570 output from +14.47 dBm to +10.37 dBm, I elected to add a 3 dB pad
between the 39 Ohm resistor and the ADE-1. This dropped the signal to +7.07
dBm according to the SA.
As I get transmitter circuitry added, I’ll report on results.
73,
Wayne
From: Thomas Sarlandie
Sent: Wednesday, October 22, 2014 1:55 PM
To: minima@xxxxxxxxxxxxx
Subject: [minima] Re: A (temporary) solution to my mixer problems
Jerry,
My wiring is very simple:
- LO pad goes directly to the cap on the output of the Si570.
- RF pad goes directly to the relay connected switching the two LPFs
- IF pad goes directly to the first crystal (no cap here)
Based on today's discussion I will look into adding the pad or 39 ohms
resistor.
Steve: I am not sure what you meant. Could you push more info on the diplexer
and buffer ideas?
thomas
On Wed, Oct 22, 2014 at 1:04 PM, Wayne McFee <nb6m@xxxxxxx> wrote:
Joe,
I agree with using the 39 Ohm resistor to get to 50 Ohms, but in tests I've
just run here, that only dropped the output into a 50 Ohm load by some two dBm.
Right now I'm seeing .985V RMS output on my scope, which correlates to just
about +13 dBm, and that's with the 39 Ohm resistor in place.
I'm also seeing +13 dBm on my power meter, which backs up the voltage
reading.
This indicates that a resistive pad would still be needed to get the output
down to the +7 dBm level.
Have you run similar tests there?
Thank you,
Wayne
On Oct 22, 2014, at 11:37 AM, Joe Rocci <joe@xxxxxxxxxx> wrote:
The Si570 drives about +13 dbm into a 50 ohm load and its output
impedance is around 13 ohms. With that assumption, all you need is a series 39
ohm resistor to the mixer LO input. This will create a nice impedance match for
the mixer and will also drop the Si570 drive level just about into the sweet
spot.
Joe
W3JDR
----- Original Message -----
From: Wayne McFee
To: minima@xxxxxxxxxxxxx
Sent: Wednesday, October 22, 2014 2:23 PM
Subject: [minima] Re: A (temporary) solution to my mixer problems
Dan,
That's right, it is simply PI network attenuator consisting of three
resistors, with two going to ground and one bridging the top ends of the two.
Like so:
In - rrrrrrr - Out
r r
r r
r r
G G
There are PI network calculators on line which will tell you what value
resistors to use.
In my case a 10 dB attenuator was needed, so I used two 100 Ohm
resistors to ground and a 68 Ohm resistor between the two.
Hope that helps.
Wayne
On Oct 22, 2014, at 11:02 AM, Mvs Sarma <mvssarma@xxxxxxxxx> wrote:
hi Dan,
IMHO , is conventional to call T or Pi attenuator a pad.(three
resistors forming a T attenuator or pi attenuator.)
On Wed, Oct 22, 2014 at 11:16 PM, Dan Reynolds <on30ng@xxxxxxxxx>
wrote:
Wayne, for us dummies can you show us what the pad looks like -
schematic. Just need a brain check.
73
Dan -- KB9JLO
https://sites.google.com/site/on30ng/
On Wed, Oct 22, 2014 at 12:05 PM, Wayne McFee <nb6m@xxxxxxx> wrote:
Thomas,
I'm into a second build of the Minima and am using an ADE-1 as
the first mixer as well.
Since the Si570 output is some +13 dBm, and the ADE-1 needs only
+7dBm LO drive, I placed a 50 Ohm resistive pad in line to reduce it down to
that level.
If you haven't yet done that, you should as that will help reduce
spurious responses from the mixer and should reduce LO leakage on transmit as
well.
I have just the receive portion built so far, so cannot yet give
you ye figures from mine.
73,
Wayne NB6M
> On Oct 21, 2014, at 9:42 PM, Thomas Sarlandie
<thomas@xxxxxxxxxxxxx> wrote:
>
> Gang,
>
> After looking at the RF386 this afternoon I came to the
conclusion that my only problem was my Minima. With -30 dBm on the output my
signal was just too low, even for the RF386.
>
> I looked into the recent discussions about mixers and wanted to
build one of them but I do not have the IC you discussed and I could not find a
clear call on which one of the JFET mixers was the best.
>
> So I took a step back and realized that (to me) this project is
more about building a working radio than running lots of mixers experiment. I
completely removed the KISS mixer from my Minima and replaced it with one of
the ADE-1 mixer that I had ordered a few months ago.
>
> My output is now at -15dBm @14.250 and -26@34.25.
>
> <dsa 201410211956.png>
>
> I should now have plenty enough power to drive the RF386!
>
> I think we should recommend this solution to new builders who
are just getting started, at least until we have a good mixer that can easily
and repeatability be built with good performance.
>
> I paid $15 for 4 of them on eBay. $3.5 a piece.
>
> Thoughts?
>
> 73,
> thomas
--
Regards
Sarma
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