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Re: LF: miniwhip not so miniresults...!

To: <[email protected]>
Subject: Re: LF: miniwhip not so miniresults...!
From: "Alan Melia" <[email protected]>
Date: Fri, 6 Oct 2006 09:39:05 +0100
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Hi Scott yes that is the sort of result I would have expected and may
explain some of the variation in reported results. The near field of the
vertical could be 300-500 yards in diameter, and certainly the coupling at
less than 100 feet is quite significant from the tests we did with a
different configuration.

As Roelof suggests I dont think there is an IMD effect due to the increased
signal level at the miniwhip but it does take the RX nearer to its problem
area.  This does not detract from the miniwhip performance because the S / N
is probably much the same and if the antenna received noise is above the rx
noise then you are in much the same position, albeit will a lower S-meter

The only reason I can think of why the intermod increased with the wire
disconnected (and a lower signal level !!) would seem to be maybe connected
to the AGC on the 897 ?? It is certainly an odd result.

Thanks for that test.

Cheers de Alan G3NYK

----- Original Message -----
From: Scott Tilley <[email protected]>
To: <[email protected]>
Sent: 06 October 2006 04:38
Subject: Re: LF: miniwhip not so miniresults...!

> Hi Alan
> The vertical and miniwhip are within 25' of each other.
> Steve, VE7SL and I did some tests tonight to determine the extent of the
> interaction.
> When one connects the vertical to a RX while monitoring the miniwhip on
> another RX the 'signal level' jumps up by many S units.  tuning through
> the 2200m band above and below reveals that the peak is shaped exactly
> like the Q curve for my vertical.  Inserting an isolation xfmr in the
> vertical feedline has no effect.  Disconnecting the antenna wire past
> the loading coil causes the signal level in the miniwhip RX to drop back
> to original levels.
> But how does this affect Miniwhip performance?
> I asked Steve to send a carrier.  I then monitored the signal using the
> miniwhip with the vertical connected to another RX.  Noise floor was
> about S7, Steve's signal when on was S9+ a dB or two...  Disconnected
> the vertical from the other RX and repeated.  Noise floor was S3 and
> Steve's signal peaked around S5 + a dB or two...  Assuming my S meter is
> fairly linear over the range it would seem that the SNR remains fairly
> constant.
> Now, how does this affect the poor FT-897D intermod rejection?
> The following surprised me at first...  Setup the FT-897D with the
> Miniwhip and connected the other RX to the vertical. I listened by ear
> to the result on the 897's speaker.  With the vertical plugged in the
> signal level jumped up as observed before.  However, the intermod level
> compared to the signal level was very low to not noticable with the rig
> set to the IPO setting (preamp off) with the internal ATT inline no
> intermod was detected.
> Hmmm....
> I then removed the vertical feedline from the other RX and, bang, up
> came the intermod even with the ATT inline.  In fact, the intermod is
> the dominate signal in the speaker and swamps out the noise!  Ok,  So I
> took a stroll out to the vertical and disconnected the antenna wire at
> the top of the coil.  The results where the same.
> Seems the Vertical and Miniwhip are interacting in a positive manner WRT
> intermod on the FT-897D.
> What this means WRT to reception of a DX signal I don't know yet.
> 73 Scott
> Alan Melia wrote:
> > Hi Scott how close are the two antennas and did you disconnect the
> > antenna, or detune it when receiving on the miniwhip?
> >
> > Cheers de Alan G3NYK

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