[VHFcontesting] [VHF] Antenna Coupling Issues

[kr7o at vhfdx.com]

I have been happy with the ICE 6 and 2m bandpass filters and they are 
inexpensive.  On 6m I run the 200w 50-50.5MHz filter after the radio and 
the 6KW filter after the 8877.  On 2M I run the 200w filter after the 
driver amp (don't think they make a high power 2m model).  My 2m yagi is 
mounted between two 6m yagis (and about 6' above the lower one).  Without 
them I had severe noise problems to the other radio when transmitting.  I 
do not notice (or sometimes only barely detect) cross band interference 
unless I am pointing directly at the shack (and that is probably 
common-mode RFI).  ICE doesn't list the 6m QRO filter on their website anymore.

I learned that filters are necessary at QRO levels with close spaced 
antennas (and probably at the 100w level depending on spacing).  One year I 
threw up a third 6m yagi on a separate mast about 5' above my HF yagi for 
the June contest and proceeded to burn out the preamp in the HF radio the 
first time I transmitted on that antenna with only 600w.


At 01:42 PM 7/11/2008 -0500, Les Rayburn wrote:
>Along with Stan, several folks have mentioned using tight bandpass filters
>on both TX and RX. I looked over DCI's filters today, and saw a few that
>might fit the deal. I'm curious has to what others are using.
>
>The bandpass filter option appeals to me as I think it would provide the
>added benefit of reducing my interference levels, and providing some
>additional protection for the pre-amps and front ends. I can't imagine that
>I'm ever going to even seriously consider running more than 200-300 watts on
>any band given the indoor antennas. It will be easy to become an "alligator"
>and certainly will only cause issues with TVI/RFI, including the potential
>to interfere with the President of the HOA who lives next door.
>
>So, sources? Prices? Anything to avoid?
>
>73,
>
>
>Les Rayburn, director
>High Noon Film
>100 Centerview Drive Suite 111
>Birmingham, AL 35216-3748
>205.824.8930
>205.824.8960 fax
>205.253.4867 cell
>
>--------------------------------------------------
>From: "Stan, W1LE" <stanw1le at verizon.net>
>Sent: Friday, July 11, 2008 11:08 AM
>To: "Les Rayburn" <les at highnoonfilm.com>
>Subject: Re: [VHF] Antenna Coupling Issues
>
> > Hello Les,   My comments are added.....
> >
> >
> > Les Rayburn wrote:
> >> 1. At what power levels (typically) does this begin to be an issue?
> >>
> > Too many variables that need controlling to comment, you are on thin ice.
> > destruct level of the preamplifier,
> > preamp isolation (filtering) for out of band signals,
> > TX power levels,
> > quality of coax being used, braided shields leak, solid shields like solid
> > copper on superflex or hardline are betrter,
> > Bypass relay isolation,
> > antenna proximity, near filed issues.
> > polarizations used,
> > Coaxial cable losses,
> > etc.
> > etc.,
> >
> >> 2. Are there steps that I can take to minimize the coupling, and protect
> >> the
> >> pre-amps and radios?
> >>
> > Coupling is proximity. Either I disable all preamplifiers not used, except
> > for the band I am playing on or
> > I have tight bandpass filters and leave the preamp on for other RX bands.
> > Tight bandpass filters for RX AND TX.
> > Another alternative is to disable all preamps on ALL bands,  when I
> > transmit on any band. including HF.
> >
> > All preamplifiers default to a bypass mode, when the system is not used.
> >> 3. What do rovers in similar situations do to prevent problems?
> >>
> >
> > Rovers usually go thru a few preamplifiers until they take the previously
> > mentioned actions.
> >
> >
> > Stan, W1LE   Cape Cod
> >
> >
> >
> >
> > ZZZZZz
> >>
> >>
> >>
> >
> >
>
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73, Robert KR7O/YB2ARO, DM07ba/OI52ee  (ex.  N7STU)
kr7o at vhfdx.com

www.vhfdx.com (KR7O/YB2ARO homepages)