[Skimmertalk] T14 Transformers

[Martin Rath]

Hi Bob,

The right angles SMA connectors are rather simple to source on ebay from
China. I can imagine that the ones used in the original board a similar
origin ( https://goo.gl/bpPXNv)

Regarding the LNA, the gain is adjustable from either -4.5 dB to +43.5 dB
OR from +7.5 dB to +55.5.dB. This high/low mode can be setup through a
jumper.

The gain as such is controlled by adjusting the voltage of pin 10 of the
AD8331 between 0 and 1 volt. The way it is integrated here is by using a
feature of the Hermes Interface that can controll a built in attenuator. If
you look at the schematic I shared this is what the MCP4725 is used for.
This is done through the i²c bus to be interfaced with an internal feature
of PowerSDR but it could most probably be done using another method.

The input of the AD8331 can be dynamically matched to 50 Ohms. This is well
described page 27 of the datasheet : http://www.analog.com/media/
en/technical-documentation/data-sheets/AD8331_8332_8334.pdf

I could not find anything related the matching of the output. In his design
DC2PD uses a single 1:1:1 transformer TR-622. I don' t have the
qualification to understand this. Maybe the output of the AD8331 is already
matched to the input of the Red Pitaya and doesn't require any further
adaptation.

73's Martin 9V1RM




On Sun, Dec 10, 2017 at 2:06 PM, Bob Wilson, N6TV <n6tv at arrl.net> wrote:

> Thanks Martin.  The pre-amplifier looks interesting.  What is the gain?
> What is the voltage requirement?  Does it include a power supply?  I assume
> it doesn't have the 14:1 transformer built-in, though it would be nice if
> it did.
>
> N4ZR managed to homebrew a transformer board using that transformer
> component, but couldn't find a male right angle PC mount SMA connector like
> the one that the Red Pitaya folks use.
>
> I'm planning to order a third batch of 14:1 transformers from the Red
> Pitaya company, which you will be able to order from me using
> http://www.kkn.net/~n6tv/XFMR once they're back in stock.  In the mean
> time, as mentioned, please email me directly (off list) if you want to be
> on the waiting list for one or more.
>
> 73,
> Bob, N6TV
>
> On Sat, Dec 9, 2017 at 3:43 PM, Martin Rath <martin.rath at gmail.com> wrote:
>
> > Hi,
> >
> > I found that the T14 transformers are available in Germany from Box73 :
> > http://www.box73.de/product_info.php?products_id=1552
> >
> > At 6.20 EUR there are not cheap especially considering the cost of
> > shipping (flat rate of 4,90 EUR in Germany / 6,90 EUR WW) but even
> > considering this I guess one could easily build there own input 14:1
> > transformer PCB for less than 15 USD a piece.
> >
> > They also have a broadband 0-60 MHz LNA designed by DC2PD for the Red
> > Pitaya ( http://www.box73.de/product_info.php?products_id=3737 ). The
> LNA
> > was described in the Funakamteur 12/2016 : I'm a subscriber so I could
> most
> > probably scan it for you if there is any interest. It will however be in
> > German :-)
> >
> > 73's Martin 9V1RM
> >
> > On Wed, Dec 6, 2017 at 3:52 AM, Bob Wilson, N6TV <n6tv at arrl.net> wrote:
> >
> >> K5TR discovered that DigiKey currently has a better price than Mouser on
> >> the Red Pitaya STEMlab 125-14 starter kit ($306.79) and acrylic case
> >> ($22.73):
> >>
> >> https://www.digikey.com/product-detail/en/trenz-electronic-
> >> gmbh/27761/1686-1034-ND/6579245
> >>
> >> https://www.digikey.com/product-detail/en/trenz-electronic-
> >> gmbh/27773/1686-1044-ND/6579255
> >>
> >> More links:
> >>
> >> https://www.digikey.com/products/en?keywords=red%20pitaya
> >>
> >> I'm currently sold-out of the 14:1 transformers (
> >> http://www.kkn.net/~n6tv/XFMR).
> >>
> >> But I can order another batch from the company if there is sufficient
> >> demand.  Please send me a direct email if you want to be on the waiting
> >> list for one or more 14:1 transformers.
> >>
> >> 73,
> >> Bob, N6TV
> >
> >
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