6300 No preselector?

Pasha Pashkin

No internal preselector and no way to use external one?
How come?

Alan Nusso, N4BV

This from Steve N5AC from an earlier post:
Superhet receivers have limited dynamic range and are forced to use filtering techniques at the front end and each stage to prevent overload.  The FLEX-6300 is a direct sampling receiver and by nature will consume the entire HF spectrum at once.  The overload point is simply the max voltage input to the A-to-D Converter (ADC) which is +7dBm (5mW) for the FLEX-6300.  This is a very large signal in the front end of the receiver and it is rare that you would encounter this level of signal. 

You could see a signal like this when there are other strong transmitters co-located with the FLEX-6300.  This is design difference in the FLEX-6500 and FLEX-6700 -- they both have preselectors. You have to decide for your environment if they will be necessary.  If you are going to run a multi-multi contest station, you will almost certainly want the preselectors.  If you are running the FLEX-6300 from your shack and do not have a next door neighbor that is a ham and runs power, you are much less likely to need preselectors.  At my house, I would never need them.

There is a broadcast filter in the FLEX-6300 which is the most likely place to find large signals so these signals will be knocked down considerably unless you are listening in that portion of the band.  If you need a more definitive answer, you can take readings at your operating point -- connect a power meter that is band limited to 1.8-54MHz and see what the total power reading on the meter is or alternately use a spectrum analyzer.  For reference, a +7dBm signal is S9+80dB!

Pasha Pashkin

Thanks for the opinion, but I need a better isolation between radios.
Does it means if I need preselector there is no way I can add it to 6300 receiver? Technically, it is not possible, am I right?
I see solution to use computer to switch external devices but not by radio.

Sergey R5AU

Pavel, i think base on this picture:

and a bit knowledge of the SSDR, you can utilize an external preselector what are compatible with external RX/TX signal where for RX you can use XVTR circuit and for TX ANT1 as default, or you can use 100watts compatible preselector (BPF) driving via DDutil 

Pasha Pashkin

Thanks,

I see it could be done by software controlled devices...my own preference is to use a hardware first as not every software is capable of providing all required setup options....much easier to do it on a hardware level.

I got idea of now, just wonder why FlexRadio decided it this way that +80db over S9 is a sufficient number

Sergey R5AU

You know everything are depends, you are in Software Defined radio community :-) It is up to you

W9OY

Put your preselector on ant 2 and your transmitter on ant 1 and use a relay to disconnect and ground antenna 2 when you transmit or you can run the Rx off transverter if you have 2 antennas or just buy a 6500

Steve-N5AC

Before you spend a lot of time trying to add a preselector, I recommend testing whether you actually need one.  The dynamic range on the radio is so large, you may find that you just don't need one.