[R-390] R-390A help needed

[Tom M.]

 I use a 4 way Mini-Circuits splitter with a DX Engineering HF preamp, and I have my R-390A hooked up with two Icoms and a Winradio.  All work fine.
Tom
    On Saturday, February 8, 2025 at 09:32:52 AM CST, Karsten Simon via R-390 <r-390 at mailman.qth.net> wrote:  
 
 To all doubters:
my splitter/combiner ist a standard circuit, many solutionss can be found on the web. From .3 to 30 MHz both output ports exhibit the same signal amplitude when each port is terminated with 50 Ohms. The difference in receiving performance is definitely that my R-390A is inferior to my 51S-1 which it should not be. I use the symmetric antenna input of the R-390A with a balun that transforms 120 Ohms symmetric to 50 Ohms unsymmetric.
-Karsten-  

-----Ursprüngliche Nachricht-----
Von: Bob Camp [mailto:kb8tq at n1k.org] 
Gesendet: Freitag, 7. Februar 2025 23:53
An: Karsten Simon
Cc: R-390 at mailman.qth.net
Betreff: Re: [R-390] R-390A help needed

Hi

Ok, this gets a bit crazy …..

A normal 3 db splitter *assumes* that it has 50 ohm loads on both outputs and a 50 ohm source. 

A typical receiving antenna is likely not a 50 ohm source. These radios do not provide 50 ohm loads. 

The net result may be a splitter that is very confused about what it should do. 

Quick and a bit stupid solution: Put 6 db pads on the input and both outputs. Now they all are much closer to 50 ohms. The splitter should be much more happy. 

No you don’t want to run things this way forever and ever. It’s just something to do to rule out the splitter as part of the problem. 

Would I bet anything on this being the issue? Nope. However it’s still worth checking. 

Bob

> On Feb 7, 2025, at 5:38 PM, Karsten Simon via R-390 <r-390 at mailman.qth.net> wrote:
> 
>> Try swapping the receiver connections at the switch and check again
> That was the first thing I had done of course
> 
> -----Ursprüngliche Nachricht-----
> Von: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] Im Auftrag von William Blodgett via R-390
> Gesendet: Freitag, 7. Februar 2025 23:34
> An: R-390 at mailman.qth.net
> Betreff: Re: [R-390] R-390A help needed
> 
> First, verify the route through the switch is “equal” to both receivers.  Try swapping the receiver connections at the switch and check again
> 
> P.S.- Both are great radios !
> 
> 73,
> Bill
> AI5RP 
> ++++++++++++++++
> Bill Blodgett
> Arlington, Texas
> USA
> 
>> On Feb 7, 2025, at 12:22 PM, Karsten Simon via R-390 <r-390 at mailman.qth.net> wrote:
>> 
>> 
>>> 
>>> are you using the same antenna for both radios?
>> 
>> Yes. Both are connected to the antenna selector switch via a two port -3db
>> splitter.
>> 
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