[CQ-Contest] What RF voltage OK at Rx in SO2R?

[i4jmy at iol.it]

Before the active devices in front end receivers there are components 
that can't withstand inherently excessive power (i.e. some attenuators 
made with 1/4W or 1/8W resistors) or can't withstand it in some (off) 
bands because reactive (i.e. some inductors of internal band pass 
filters).
Apart the above considerations about the equipment survival, there is 
the operational aspect that, in spite of the high claimed RX I.P. 
suggest always to minimize the applied signal to the RX antenna 
connector in order to receive decently while a TX (or several ones like 
in a MM) is keyed. Several tens of dB below the I.P. are highly 
recommendable in common situations. 
Effective pass band filtering ahead of RX, and harmonic suppression at 
TX side (stubs) work quite efficiently in this direction.
When antennas are not spaced enough, and expecially if multiband, the 
required attenuation to obtain a safe and satisfactory situation could 
be quite a big deal.
When measuring first time what sort of signal is coming down, act as 
you where working with your precious spectrum analyzer, put some 20/30 
dB power attenuator ahead of your instrumentation.

73,
Mauri I4JMY



> ---------- Initial message -----------
> 
> From    : owner-cq-contest at contesting.com
> To      : <cq-contest at contesting.com>
> Cc      : 
> Date    : Mon, 24 Sep 2001 08:04:55 -0000
> Subject : Re: [CQ-Contest] What RF voltage OK at Rx in SO2R?
> 
> 
> 
> I lost W2SC email address due to BadTrans virus infection received 
from one
> of cq-contest reflector recepients so let me answer Tom's question 
here.
> 
> Yaesu puts low voltage bulb ahead of 4 diodes.  Cold bulb has a very 
low
> resistance of few Ohms and doesn't affect RX sensitivity much.
> High RF makes it glow with much increased resistance.  I had 12 V car 
bulb
> as an emergency light in my shack when long wire antenna was 
connected and
> local 300 kW AM BC TX was runing :-)
> RX didn't work without it as switching diodes were A_mplitude 
M_odulated.
> BCI rejection filter was later installed.
> 
> 73 de Mario, S56A, N1YU
> www.miletic.net or http://artinian.bit.si/radio.htm
>   ----- Original Message -----
>   From: Marijan Miletic, S56A
>   To: 'Marijan Miletic, S56A'
>   Sent: Monday, September 24, 2001 7:56 AM
>   Subject: RE: [CQ-Contest] What RF voltage OK at Rx in SO2R?
> 
> 
>   Mario -
> 
>   This is a much better idea than 1/16 amp fuses.
> 
>   I assume that your circuit is two diodes in series forward biased 
toward
>   ground and two in reverse to clip both peaks of the wave.  I would 
presume
>   that a relay between the signal and the diodes is necessary to 
disconnect
>   them during Xmit.
> 
>   Do you think the diodes could take it if there really were 7V on 
the input
>   or should I try 4 diodes each way?
> 
>   73, Tom W2SC 8P1A
> 
>   -----Original Message-----
>   From: Marijan Miletic, S56A [mailto:artinian at siol.net]
>   Sent: Sunday, September 23, 2001 8:59 AM
>   To: cq-contest at contesting.com; Jerry Flanders
>   Subject: Re: [CQ-Contest] What RF voltage OK at Rx in
>   SO2R?
> 
> 
>   1W or 7 V RF at 50 Ohms is a safe bet for RX survival.  You
>   might install
>   two pairs of back-to-back protection Si diodes to keep RF at
>   1,5 V which is
>   also within IMD3 RX capabilities.
> 
>   Using bandpass filters is highly recommended.  Coax stubs
>   are cheaper
>   solution due to lower Q.
> 
>   WRTC-2000 measurements with 100 W TX and tribander showed
>   about 3 V RF on
>   nearby wideband 40 m long Windom antenna.
> 
>   73 de Mario, S56A, N1YU with few smoked RX repaired.
>   www.miletic.net or http://artinian.bit.si/radio.htm
> 
> 
>     ----- Original Message -----
>     From: Jerry Flanders
>     To: cq-contest at contesting.com
>     Sent: Sunday, September 23, 2001 2:43 PM
>     Subject: [CQ-Contest] What RF voltage OK at Rx in SO2R?
> 
> 
> 
>     I am trying to set up for RTTY SO2R and have two
>   questions:
> 
>     1. What voltage levels can solid state rigs safely
>   tolerate from nearby
>   tx?
> 
>     2. I read about guys using stubs as well as filters in
>   SO2R. How much of
>     this is just to protect the rx hardware, and how much is
>   there to improve
>     normal rx on band A while tx on band B is underway?
> 
> 
> 
>     I would like to avoid smoke testing the rx front ends on
>   my FT-1000D and
>     IC-756PRO if possible. I intend to measure actual voltage
>   present on my
>     (well separated) rx antennas while transmitting and
>   determine from that if
>     I actually need protection, and to what degree. This is
>   aside from the
>     question of rx overload, which I can see for myself once I
>   get it all in
>     actual operation. My immediate goal is to see if I can
>   safely tx w/o smoke
>     before I start working with stubs or filters.
> 
>     Jerry Flanders  W4UK
> 
> 
> --
> CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
> Administrative requests: cq-contest-REQUEST at contesting.com
> 
> 


--
CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST at contesting.com