[hpsdr] Proposal for a 'low-end' RX/TX board for HPSDR

[Eric Ellison]

Ray

 

By the way thanks for the updates to the Wiki today.

 

Eric

 

 

  _____  

From: hpsdr-bounces at hpsdr.org [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of
Ray Anderson
Sent: Monday, July 24, 2006 4:44 PM
To: hpsdr at hpsdr.org
Subject: Re: [hpsdr] Proposal for a 'low-end' RX/TX board for HPSDR

 

 

 

 

>> I can see the argument for the front end LNA at 10 meters (or maybe even

>> 15 meters), but on the bands below that I think it may actually be a

>> liability unless you have an extraordinarily high IP3 for the preamp.

>> While this can be done it comes at the expense of quite a  bit of DC

>> current. This may not be a big deal but is something to be considered.

 

>Typicaly the LNA will take 60-80mA. Compared to what will disappear on tx

>it pretty insignificant. One advantage of some amplification will be to 

>lift rx noise floor compared to the spurs and sprogs from the LO and DIG 

>inside the enclosure!

 

>Ulrich suggested I think the BFG591 as a SMD alternative to the 2N5109 for

>mixers and amp. Maybe the part would go well either in a Norton

>configuration or the Mahkinson (N6NWP) MRF586 push pull pre-amp.

 

>Shel CT1IZU

 

 

Shel-

 

Good comments. Upon further consideration I tend to agree with you. 

 

The performance of a QSD can also be improved by including a diplexer
between the BPF and the QSD to properly terminate the QSD input out of band.
By utilizing the preamp the noise figure at higher frequencies is improved
and the QSD also sees a constant termination impedance across a wide band
since the amp exhibits 50 ohm input and output Z.

 

I've recently placed a schematic of a typical Norton amp on the Phoenix Wiki
page. The schematic shows feedback turn s ratios set up for about 9.5 dB
gain. Can anyone comment on what attributes the Makhinson (N6NWP) circuit
(which is essentially a pair of Norton amps in push-pull) brings to the
table that would make it preferable over the Norton amp in this application.

 

Does anyone have some target figures regarding performance that we should
aspire to obtain? I think an IP3 of +40dBm with a dynamic range of at least
100 dB and a noise floor in the vicinity of -130 to -140 dbm are in the
ballpark for state-of-the-art HF front ends these days.

 

I'm currently evaluating various options as far as preamps, QSD circuits,
filtering etc. are concerned. If anyone has any favorite implementations
that may be appropriate to Phoenix I'd like to see them during this
evaluation phase.

 

73,   Ray   WB6TPU

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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