RedPitaya and MOBO Combination

[Takehiko Tsutsumi]

Hi,

I have been enjoying  Mobo4.3 as HF main rig for these two years but I obtained a RedPitaya board to see the world of direct sampling SDR technology.

See http://redpitaya.com/

In fact, It is quite easy to setup PowerSDR mRX PS SDR configuration and the functionality is quite impressive as long as I use it as a simple receiver coverring from LF to 6 meter.

Now, I am wondering somebody is making his/her efforts to hook RedPitaya to MOBO4.3 board to make 1X1 tranceiver.

Any response?

Regards,

take

de JA5AEA

[VK5ZAG]

Too expensive. Buying a complete kit or off shelf transciever better option at this time. Later?

[f6itu]

Hi

As you probably already noticed, adding filters to the RX path of the Redpitaya is useless, unless you live close to a high powered broadcast transmitter. And I frankly don’t really see how it could be possible to simply hook up a Mobo to the Pitaya. A bpf could lightly improve the level of the noise floor, but at a cost: you won’t be able to use your pitaya in wide band/multi RX mode (imagine you can use cwSkimmer from 1 to 60 MHz, or spot any JT65 or RTTY transmission as well).

On the TX path, it’s definitely not the same problem. You need a low pass filter. And this filter should be installed after the power amp you intend to use. That means the original mobo filter will never  be strong enough to handle the power (and probably not stiff enough to reject undesired harmonics too).

You’ll have to design a specific lpf for this, or use a already designed one (the G4TZR could be a good answer to your problem)

http://www.radio-kits.co.uk/radio-related/G4TZR_LPF/G4TZR_LPF.htm

 btw, the 20 W G6ALU on the same website could be a nice candidate for the power amp section :- ))

VY 73’

Marc f6itu

[tom]

Hi,

My mobo has been working great but I wanted to minimize the ground loop
hump on the PSDR spectrum display. I tried inserting transformer
isolation between the receive I/Q outputs and the PC sound card input
(using a Wb9yig stereo adapter to M-audio Delta 44). When I inserted the
transformers for isolation, I was unable to eliminate images. When I
checked the DB values for L and R channels I found a 20 db spread. Just
to experiment, I eliminated the transformers and jumpered the tip to tip
and ring to ring on the stereo jacks mounted on a minibox with 1 inch
lengths of wire and I was still seeing a 20 db difference in I and Q
levels. I tried running image suppression routing in PSDR with no success.

Can anyone explain why this is happening (assuming anyone is still
monitoring this list)?

Tom
w1tsl

[Silverfox]

It is not caused by RF. It is an artifact of the signal processing. Others may be able to indicate why it is there.
Alan - W6ARH

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[Alan]

Original Message -----
Subject: RE: [MOBOKITS]Mobo I/Q question

. Just to experiment, I eliminated the transformers and jumpered the tip to tip and ring to ring on the stereo jacks mounted on a
minibox with 1 inch lengths of wire and I was still seeing a 20 db difference in I and Q levels.

Tom

Do you mean you are sending a mono signal to the D44?
Then there should be no image suppression, exact mirrors.
Check the D44 control panel.
Do not use monitor mixer.
Make sure the gains are set the same for both channels.

73 Alan G4ZFQ

[tom]

Thanks for the responses...No Alan, all I did was insert a small minibox
with a pair of stereo jacks mounted to it and jumpered the tip of one to
the tip of another and the ring of one to the ring of the other. Prior
to doing this, the L and R channels were equal within a fraction of a
db. After placing the box in line with the I/Q feed from the mobo, the L
and R channels were 20 db apart from each other. I have never been able
to change PSDR audio parameters by adjusting the Delta 44 control panel.

What I'm trying to do is minimize the ground loop spike on the PSDR
display by isolating the I/Q outputs to the sound card with a pair of
600 ohm 1:1 transformers in the minibox but the 20 db spread of the two
channels is always there until I disconnect the minibox and directly
reconnect the I/Q cable from the mobo to the Delta44 input after which
the two channels balance again.

I have also tried eliminating the two transformers coupling the tips and
rings and replacing them with a pair of 0.47 mfd capacitors with the
same results. I can't see how using a pair of identical caps or
transformers should unbalance the two channels by 20+ db. I have
attempted to run the image rejection in PSDR with the caps/xformers and
even using straight through short (1") wires connecting tip to tip and
ring to ring on the two stereo jacks in the minibox with the same
imbalance issue.

I hope I'm describing the situation clearly. Pls feel free to ask
questions...

Tom
w1tsl

[Takehiko Tsutsumi]

Hi,

I went to different direction to QRO from 10mW RedPitaya to 100W. See my following blog.

playredpitaya.blogspot.com

TS-680S pre-selector works well to suppress broadcast trasmitter signals on 160m.

Regards,

take

de JA5AEA
2016年7月11日月曜日 15時11分38秒 UTC+9 f6itu: