[Heathkit] SB-610 scope to SB-303 receiver

[jeremy-ca]

A dead short to ground would certainly affect sensitivity. However we are 
trying to accomplish two things in this hookup.

1. Not overdrive the SB-610
2. Not load down the IF stage.

A very low value of coupling cap will accomplish both.
You can calculate the Xc of the circuit and see its effect on the IF.

Carl
KM1H

----- Original Message ----- 
From: "Tom Chesek" <tchesek at epix.net>
To: "Bob Macklin" <macklinbob at msn.com>; "Dan Pividal" 
<dpividal at tampabay.rr.com>; "heathkit at mailman.qth.nt" 
<heathkit at mailman.qth.net>
Sent: Wednesday, December 12, 2007 6:19 AM
Subject: Re: [Heathkit] SB-610 scope to SB-303 receiver


> I'm jumping in here with a question. If you shunt signal to ground does 
> this
> affect the receiver sensitivity?
>
> Tom K3TVC
>
>
> ----- Original Message ----- 
> From: "jeremy-ca" <km1h at jeremy.mv.com>
> To: "Bob Macklin" <macklinbob at msn.com>; "Dan Pividal"
> <dpividal at tampabay.rr.com>; "heathkit at mailman.qth.nt"
> <heathkit at mailman.qth.net>
> Sent: Tuesday, December 11, 2007 8:12 PM
> Subject: Re: [Heathkit] SB-610 scope to SB-303 receiver
>
>
>> 10:1 of almost nothing is still almost nothing. The issue is how LITTLE 
>> of
> a
>> signal is required to drive the scope and not the amount shunted to
> ground.
>>
>> Carl
>> KM1H
>>
>>
>>
>>
>> ----- Original Message ----- 
>> From: "Bob Macklin" <macklinbob at msn.com>
>> To: "jeremy-ca" <km1h at jeremy.mv.com>; "Dan Pividal"
>> <dpividal at tampabay.rr.com>; "heathkit at mailman.qth.nt"
>> <heathkit at mailman.qth.net>
>> Sent: Tuesday, December 11, 2007 7:37 PM
>> Subject: Re: [Heathkit] SB-610 scope to SB-303 receiver
>>
>>
>> >A 2pf cap connected in series with a 22pf cap produces a 10:1 voltage
>> >divide
>> > at any frequency!
>> >
>> > Bob Macklin
>> > K5MYJ
>> > Seattle, Wa,
>> > "Real Radios Glow in the Dark"
>> > ----- Original Message ----- 
>> > From: "jeremy-ca" <km1h at jeremy.mv.com>
>> > To: "Bob Macklin" <macklinbob at msn.com>; "Dan Pividal"
>> > <dpividal at tampabay.rr.com>; "heathkit at mailman.qth.nt"
>> > <heathkit at mailman.qth.net>
>> > Sent: Tuesday, December 11, 2007 4:29 PM
>> > Subject: Re: [Heathkit] SB-610 scope to SB-303 receiver
>> >
>> >
>> >> Luckily, 22pf has minimal effect at the frequency of interest.
>> >>
>> >> Carl
>> >> KM1H
>> >>
>> >>
>> >> ----- Original Message ----- 
>> >> From: "Bob Macklin" <macklinbob at msn.com>
>> >> To: "jeremy-ca" <km1h at jeremy.mv.com>; "Dan Pividal"
>> >> <dpividal at tampabay.rr.com>; "heathkit at mailman.qth.nt"
>> >> <heathkit at mailman.qth.net>
>> >> Sent: Tuesday, December 11, 2007 5:37 PM
>> >> Subject: Re: [Heathkit] SB-610 scope to SB-303 receiver
>> >>
>> >>
>> >> > Remember that coax like RG-174 is about 22pf/ft. The coupling cap 
>> >> > and
>> > the
>> >> > capacitance of the coax will be a voltage divider.
>> >> >
>> >> > You want to use the smallest possible coupling cap to reduce the
>> >> > loading
>> >> > on
>> >> > the IF stage. I would recommend using a GIMMICK.
>> >> >
>> >> > Bob Macklin
>> >> > K5MYJ
>> >> > Seattle, Wa,
>> >> > "Real Radios Glow in the Dark"
>> >> > ----- Original Message ----- 
>> >> > From: "jeremy-ca" <km1h at jeremy.mv.com>
>> >> > To: "Dan Pividal" <dpividal at tampabay.rr.com>;
> "heathkit at mailman.qth.nt"
>> >> > <heathkit at mailman.qth.net>
>> >> > Sent: Tuesday, December 11, 2007 1:35 PM
>> >> > Subject: Re: [Heathkit] SB-610 scope to SB-303 receiver
>> >> >
>> >> >
>> >> >> Well at first you said bypass and now you say coupling; there is a
>> >> >> huge
>> >> >> difference.
>> >> >>
>> >> >>  Mmf is now pf;  mf is still mf.
>> >> >>
>> >> >> Either the manual has a typo or you need glasses or maybe both <G>
>> >> >>
>> >> >> A very low value of 1-12pf is more like it and you select a value
> that
>> >> >> doesnt overdrive the scope. Use a trimmer if you have one and then
>> >> >> measure
>> >> >> the value that gives the best results and replace with a fixed
> value.
>> >> >>
>> >> >> For such a short run any miniature coax is OK, RG-174, 178 and 179
> are
>> >> >> common ones.
>> >> >>
>> >> >> Carl
>> >> >> KM1H
>> >> >>
>> >> >> ----- Original Message ----- 
>> >> >> From: "Dan Pividal" <dpividal at tampabay.rr.com>
>> >> >> To: "heathkit at mailman.qth.nt" <heathkit at mailman.qth.net>
>> >> >> Sent: Tuesday, December 11, 2007 3:46 PM
>> >> >> Subject: [Heathkit] SB-610 scope to SB-303 receiver
>> >> >>
>> >> >>
>> >> >> >I am trying real hard to hook up an SB-610 to an
>> >> >> > SB-303.
>> >> >> > If anyone has done the mod to monitor the receive envelope please
>> >> >> > let
>> >> >> > me
>> >> >> > know what value of coupling capacitor you used with success.
>> >> >> > Seems the Heathkit SB-610 assembly manual says to use a 1.0mmf
>> >> >> > Also says, they supplied the 1.0mmf as well as a 2.2mmf and a
> 12mmf
>> >> >> > capacitor in the original kit.
>> >> >> > I believe that long ago mmf meant Picofared.
>> >> >> > That would make a big difference.
>> >> >> > Tech notes I have from Heathkit says to use a 1.0mf coupling cap
> to
>> > the
>> >> >> > 3rd IF via a RG174 coax to a spare RCA plug in the back of the
>> >> >> > receiver.
>> >> >> > To which document do I pay heed.
>> >> >> > Thanks in advance for any help in clearing this up.
>> >> >> > Dan/N4VET
>> >> >> >
>> >> >>
>> >> >>
>> >> >
>> >> >
>> >>
>> >>
>> >
>> >
>>
>>
>>
>>
>> -- 
>> No virus found in this incoming message.
>> Checked by AVG Free Edition.
>> Version: 7.5.503 / Virus Database: 269.16.17/1178 - Release Date:
> 12/8/2007 11:59 AM
>>
>>
>
>