TRX2 More narrow filter

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TRX2 More narrow filter

Postby N7KG » 14 Aug 2012 19:30

I am contemplating purchasing the TRX2A and am wondering if there is a mod to make a filter more narrow than the 1k. Thanks.

Brett, N7kg
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Re: TRX2 More narrow filter

Postby OH2NLT » 15 Aug 2012 08:54

Hello Brett
there is adjustable SCAF type filter in the TRX2. With push button you can quickly select one of the three setups. Each setup upper edge is adjustable. Following picture and the user manual explains the SSB/CW filter operation.

http://www.jumaradio.com/juma-trx2/adju ... filter.jpg


Block diagram of the TRX2 gives you additional information how the RX and TX signal path is configured.

http://www.jumaradio.com/juma-trx2/trx2 ... -block.pdf

73 Juha oh2nlt
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Re: TRX2 More narrow filter

Postby F6DEX » 17 Aug 2012 15:45

Juha

Yes, of course the SCAF filter is adjustable but it is not in the agc loop...

I also think it could be interesting to be able to reduce the bandwith of the first (roofing) active filter in CW by simply changing the components of the RX Filter plug-in board (SSB is OK but CW is too wide). Do you think possible to redesign this board and to offer an additional kit for those who prefer a narrower bandwith ? Or only to seel the board alone and/or to indicate the mods for 500Hz or at least 700Hz (my measurements show it is about 1100 or 1200) ?

An other question : the CW sidetone level is to strong : can you please give us a simple way to reduce it ?

Regards, Laurent F6DEX
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Re: TRX2 1st filter and sidetone level

Postby OH7SV » 19 Aug 2012 05:53

Hello Laurent,

You are right that the 1st filter is a "roofing" filter which is in the AGC loop. We know the properties of the 1st filter. It is compromize of selectivity and noise. Noise is the reason for its response because sharp active filters are easily bad noise generators. I have been working with better 1st filter using elliptic notches in the lowpass slope. It is only simulated and let't see when I have enough time to build a prototype.

TRX2 sidetone is tracking the AF gain. Sidetone level can be reduced by increasing the value of resistor R52 in the main board e.g. -6dB by 470k => 1M.

73 Matti OH7SV
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Re: TRX2 More narrow filter

Postby F6DEX » 19 Aug 2012 16:37

Thank you Juha, Matti.
Trx2 is a fantastic rig with extremely good audio (rx and tx). mine worked the first time I powered it on: what a pleasure. 73, Laurent
Last edited by F6DEX on 06 Sep 2012 17:36, edited 1 time in total.
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Re: TRX2 More narrow filter

Postby M5FRA » 23 Aug 2012 07:23

As I operate 99% CW a narrow roofing filter is a priority. In the past I have played with DC RX boards like the R2Pro with a Tayloe mixer and they make very quiet receivers. The big problem has been getting the selectivity down enough to make CW comfortable. In one rig I used a SCAF outside the AGC and while good it was far from the best solution. I have been looking at the TRX2 as an alternative to the KX3 as a /P rig but the narrow filter issue is steering me away from it which is a pity.

Colin - G8FRA/M5FRA
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