[minima] Re: A (temporary) solution to my mixer problems
- From: Thomas Sarlandie <thomas@xxxxxxxxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Wed, 22 Oct 2014 13:55:36 -0700
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 <nb6m@xxxxxxx>
> *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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