[Fourlanders] DCI Bandpass Filter - High Reflected Power

[Rogers, Ron]

Yes, when the amp is in standby, then the filter IS in the TX path of the barefoot radio. 


Ron 

-----Original Message-----
From: fourlanders-bounces at contesting.com [mailto:fourlanders-bounces at contesting.com] On Behalf Of Brian McCarthy
Sent: Tuesday, September 07, 2010 11:57 AM
To: Fourlanders
Subject: Re: [Fourlanders] DCI Bandpass Filter - High Reflected Power

Good points Ron,

I did use different jumpers of both differing length and material. I terminated the filter with jumpers routed through another relay and onward to a dummy or directly to dummy loads. Three different dummy loads were in use at different times. While trying to reduce the variables, two of the dummy loads were connected directly to the filter (one at a time).

Yes, I could very easily add the filter into the receive only side of the circuit, but I always thought it was good insurance for reducing out of band and harmonic radiation from the transverter to keep it in the transmit path. The reflection percentage occurs with the same magnitude with two different transverters. With about 30% reflected, that roughly a 4:1 VSWR. I don't really want that level of poor performance in my receive chain.

Just curious Ron, if your amp is in standby, is the filter remaining inline in the "barefoot" transmit path?

Tom, thank you for the offer to help diagnose it. I may take you up on that, but I know there won't be time to do it before the contest.

Brian
NX9O


On Tue, Sep 7, 2010 at 9:47 AM, Rogers, Ron <RR124640 at ncr.com> wrote:
> I doubt you are going to find any physical flaws in the filter.
>
> Those 4 stage helical chamber filters have been found to be sensitive to the capacitance variables introduced by the connecting coax leads. Be sure to try other coax jumpers.
>
> With the way my amps are designed using a pair of external Dow Key relays, I've never been concerned with the SWR on DCI filters SWR over the years. I always insert them into the RX line only.
>
>
> Ron
> WW8RR
>
> -----Original Message-----
> From: fourlanders-bounces at contesting.com 
> [mailto:fourlanders-bounces at contesting.com] On Behalf Of Brian 
> McCarthy
> Sent: Tuesday, September 07, 2010 9:27 AM
> To: Fourlanders
> Subject: [Fourlanders] DCI Bandpass Filter - High Reflected Power
>
> I know that we have had occasional problems with filters used for the 
> contests. My DCI-223.5-3H has developed a problem. With 30 watts in at
> 222 MHz I get 10 watts returned. I have opened up the unit. I found no obvious problems. I closed it back up, but made sure to carefully clean the center contacts on the SO-239's (MEK and cotton swabs). No change. I guess I will open it up again and check for hairline fractures, or bring it to work where I can reheat the joints with one of the monster soldering irons.
>
> One added data point of information, I NEVER feed the output of the amp through the filter. I always use it between the transverter and the Lunar Link.
>
> Does anyone have any other suggestions?
>
> When we had trouble before with DCI filters, what were the failure modes?
>
> Does anyone have a similar filter appropriate for 222 MHz that I could conveniently borrow?
>
> Thank you!
> Brian
> NX9O
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