[IRCA] Re: Modern Ham Transceivers Vs. Drake R8B

["Don Moman" <ve6jy@xxxxxxxx>]

I am really fond of the ICOM 756PRO series (have a couple of the PRO and
just recently, the new PROIII) for SWLing in general but they loose lots of
sensitivity below 1.6 mhz. With a fixed ~10db attenuator in the input <1.6
filter plus neither of the preamps function there, so you are loosing approx
20 to 25db here. If you are in a quiet area or using a low output antenna,
you certainly "need" to make this back up.  I believe this is true of the
746PRO as well, but my mod comments only apply to the 756PRO series.

The fixed attenuator built into that <1.6 mhz filter section isn't too hard
to bypass, if you can handle tiny smt work. I have done this (I know Guy
Atkins has too) on both of my
PRO's, but not the PROIII yet (it still needs it removed). There is a way to
trick the preamp -  Dallas Lankford came up with this idea - by cutting 2
traces and reversing them, so the preamp is on when you turn it off, you get
the idea.  I can see where to do it on schematic but haven't translated that
to where it actually needs to be done on the board.  In this respect, the
PROIII may be easier to mod as the preamps are mounted on a daughter board
above the main board. I have not yet attempted this mod on either the PRO or
PROIII.  It would have been so simple, at the design stage to allow the
preamps to be enabled, but as usual, we are stuck with what the designers
think should be sufficient.

At least if the internal att is bypassed, one can add external amplification
without loosing 10db of precious headroom, but letting the internal preamps
function would sure be handy.   I did break the RX line internally after the
TX/RX relay and bring it out to the rear, so I have true TX antenna OUT and
RX IN  (like older ICOMs with the little phone plug jumper) which adds a lot
of flexibility for external amplification and filtering.

I have heard that the 7800 does allow the preamp(s?) to function below 1.6
mhz.  Also that while it mentions AM-Sync, it is not yet implemented in the
upgradeable software.

73 Don
VE6JY

----- Original Message -----
From: "Les Rayburn" <les@xxxxxxxxxxxxxxxx>
To: "NRC AM List" <am@xxxxxxxxxxx>
Cc: "IRCA" <irca@xxxxxxxxxxxxxxxx>
Sent: Monday, February 07, 2005 16:30
Subject: [IRCA] Modern Ham Transceivers Vs. Drake R8B


> I'm curious if anyone on the list(s) has had a chance to test the modern
> DSP driven rigs such as the Icom 756 ProIII, Icom 7800, Icom 746 Pro,
> Ten Tec Orion, etc. for broadcast band DXing?
>
> Modern amateur transceiver design is being driven by receiver
> development...with
> the primary design criteria being enhanced performance during contest
> and DXing conditions. Namely, the ability to detect a very weak signal
> nearby a very strong signal. Third order intercept points, etc.
>
> These transceivers now incorporate advanced roofing filters, DSP
> engines, and variable IF bandwidths that should make them superior for
> our purposes of BCB DXing as well.
>
> I keep hoping that we'll soon see these improvements introduced in
> a receive only box...but lacking that, I can imagine that many
> DX'ers might be tempted to purchase an Icom 746 Pro at
> around $1,500 as opposed to the much older technology in
> a Drake R8B at nearly $2,000.
>
> All but the Icom 7800 lack synch AM, but that feature rarely helps
> with weak DX anyway...and the greater capability in terms
> of IF-DSP would seem to more than make up for it.
>
> Very interested in comments on this topic.
>
> 73,
>
> Les Rayburn, N1LF
>
>
>
>
>
>
> Les Rayburn, director
> High Noon Film
> 100 Centerview Drive Suite 111
> Birmingham, AL 35216-3748
> 205.824.8930
> 205.824.8960 FAX
> 205.253.4867 CELL
> http://www.highnoonfilm.com
> 205.253.4867
>
>
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