[minima] Re: A (temporary) solution to my mixer problems
- From: Wayne McFee <nb6m@xxxxxxx>
- To: "minima@xxxxxxxxxxxxx" <minima@xxxxxxxxxxxxx>
- Date: Wed, 22 Oct 2014 13:04:33 -0700
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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