Measures (K6???) did a relay speed-up scheme for QSK on an SB220, I don't
remember the details but it was something like hitting the relay with higher
than usual coil voltage/current and it shortened up the relay pull-in time.
It might be more complicated in this application than needed. I don't have
the URL to Measures' site but it can probably be found by a search.
73, Larry W6NWS
-----Original Message-----
From: Douglas Ruz (CO8DM)
Sent: Sunday, August 30, 2015 8:41 AM
To: Tom W8JI ; Charles Cu nningham ; 'topBand List'
Subject: Re: Topband: KD9SV-OK1RR relays ???
Tom and all members of the list thanks for your ideas and time !!!!.
I have a plan B:
I added a BNC female connector in the rear panel of my old Yaesu, FT747 (It
is an FT80C, the commercial version with metallic chassis) few months ago.
I was using that BNC to feed an SDR receiver using the same antenna.
If i add a SPDT switch also on the rear panel and RE-WIRE the BNC connection
i can get an RX port in my old radio and can connect an RX antenna...like
modern radios...Switch Pos A (main antenna at SO239)...Pos B (SO239 for TX
and BNC for RX)...i made few mods to my radio, so, i know it very well...
Maybe that will help...of course, i must add then an Front End Saver...still
need a fast relay !!!
Maybe the Plan A with a 5mS relay will be more easy...still need a fast
relay too !!!
73....Douglas, CO8DM
"No creo que haya alguna emoción más intensa para un inventor que ver alguna
de sus creaciones funcionando. Esa emoción hace que uno se olvide de comer,
de dormir, de todo." - Nikola Tesla
----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "Charles Cu nningham" <charlie-cunningham@nc.rr.com>; "'topBand List'"
<topband@contesting.com>
Sent: Sunday, August 30, 2015 12:27 AM
Subject: Re: Topband: KD9SV-OK1RR relays ???
It seems to me that a very fast operating preamp protection circuit could
be
constructed employing a good fast saturating NPN switching transistor
across
the antenna path. In receive mode the collector-base junction would have
substantial reverse bias and the transistor can be chosen for low
collector-base capacitance. With a fast switch like a 2N708 or something
similar the switching time will, of course, FAR outperform a relay
closure
time.
This thread might have splintered. I was responding to this:
<<Your FT-747 only has one antenna input. It does not have a second
<<receiver. It doesn't even have a receive-only antenna input. You cannot
<<transmit and receive at same time. Why do you need a "front end saver"?
If it is a transceiver without an RX antenna point, the problem is adding
a receive antenna to a transceiver that does not have a receive port.
If it is a transceiver with an RX port, the requirement for an external
"front end saver" and what will work depends on the antennas, the power,
the transceiver, and the antenna spacing.
A front end saver can be very simple with some radios, more complicated,
or not needed at all.
An external switch is never easy to do correctly, unless the radio has
good TX RX switching time sequencing.
I'm unclear what the application is, but a 10 mS relay is really too slow
for either application. The sequencing issues I pointed out apply to both
systems.
73 Tom
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