[CQ-Contest] Bandpass FIlters

[Jim Brown]

On 4/25/2021 10:02 AM, Drew Vonada-Smith wrote:
> However, a decent filter is rated to 2:1 at least. 

It's important to define "decent" in this context. The inexpensive ones, 
ICE and Dunestar, will NOT tolerate SWR, even at 100W. Caps in these 
filters WILL fry, and when they are replaced, the filter must be 
re-aligned on good lab instrumentation.

By contrast, the filters based on W3NQN designs sold by Array Solutions, 
5B4AGN's TXBPF kits, and the Bandmaster sets, also sold by Array 
Solutions, are much more robust. They are also vastly superior filters. 
Here's a report on lab work I did around 2014 that was published in 
National Contest Journal. http://k9yc.com/BandpassFilterSurvey.pdf


  However, I fear this is not going to be your main problem.  The IC7300 
is notoriously bad in a multi transmitter environment like FD, and your 
band filter will not help with in band noise that they create.  Nor will 
a roofing filter.  No filtering at the K3 can help, because the noise 
is*actually there*.  Depending on your circumstance, antenna spacing, 
band choices, etc, you may or may not be OK, but the 7300 is a bad 
choice for a FD radio.  Convince them to bring something better.  That 
does not necessarily mean expensive.  Some reasonable cost radios are 
good at this.  (TS590 is a great example).

Also great advice. A used Elecraft K3 or K3S is even better, and I've 
heard that the 6000-vintage Flex rigs are pretty clean (although the RX 
in the Flex rigs may not have sufficient dynamic range for multiple 
transmitters on the same band). And thanks to the introduction of the 
Elecraft K4, used K3s and K3Ss are approaching the price of new 590.

Here are slides for a talk I gave at the last Visalia DX convention on 
Multi-Transmitter operation. It addresses all of the issues Drew raised, 
and more.

  http://k9yc.com/Multi-Station.pdf

73, Jim K9YC