Several preselectors were produced by commercial vendors, some time ago, not
likely as good a preselector as yours, but they offered RF sensing to pass the
TX signal around the preselector.
This seems to be a better solution than modifying the radio.
For those not comfortable with RF sense switching, one might consider using the
PTT line to switch around the preselector.
With most TT radios, these lines are very fast (for QSK) and could be in
parallel with the linear key line if a linear is used.
‘Gary
> On Sep 13, 2016, at 5:55 AM, rick@dj0ip.de <Rick@DJ0IP.de> wrote:
>
> Correct, my pre-selector is RX only, which the name implies.
> That is why every transceiver I have had since the mid 70's was immediately
> modified with two RCA phono jacks mounted on the back. I interrupt the RX
> ANT line internally and run it thru the two jacks, jumpered of course when
> no preselector is attached. Even my Eagle has this mod. The OM7 had it
> available but very few people performed the mod. I did it on the OM7 I
> tested here prior to its announcement and it made a WORLD of difference on
> 40m.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt, Germany)
>
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of shristov
> Sent: Tuesday, September 13, 2016 10:15 AM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Scads of used Icom IC-7300
>
> "rick@dj0ip.de" <Rick@DJ0IP.de> wrote:
>
>> However the Dunestar SPECS on their web site claim 40dB band-to-band
>> rejection. I was just quoting the specs.
>> http://www.dunestar.com/store/Single-Band-Bandpass-Filters-pid-4.html
>
>
> Hi Rick,
>
>
> that's what I had in mind.
> Taking the 7 MHz filter as an example,
> there is 40 dB attenuation on ~3.5 MHz.
>
> But on 6 MHz the attenuation is practically nil.
>
> Your preselector is the right tool for the job.
> But it's receive-only, given the 7.5 dB passband attenuation.
>
> Dunestar etc filters must have a much wider passband in order to achieve low
> enough passband attenuation, making them suitable for transmitting.
>
>
> Best 73,
>
> Sinisa YT1NT, VE3EA
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