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 vertical
antenna, or detune it when receiving on the miniwhip?
Cheers de Alan G3NYK
----- Original Message -----
From: Scott Tilley <[email protected]>
To: <[email protected]>
Sent: 05 October 2006 02:13
Subject: Re: LF: miniwhip miniresults...?
Roelof and other interested parties
Last night I meet with some success with the miniwhip and noted some
interesting things about my radios.
I compared the 'large' vertical (50') with my TS-440 as a receiver
against the FT-897D and the miniwhip.
After sunrise back east where a large storm was brewing the noise floor
dropped and up came VY1JA on both setups. I got far better signals on
the vertical but surprising good signals on the miniwhip that was
sitting on the roof of my greenhouse.
This evening I mounted the miniwhip on my 20' carbon fibre fishing and
stuck it up about 30' above the back yard in the same spot on the
greenhouse as I ran last night. Boom! Up came the local 'warbler'
believed to be a local PLC signal; however, so did the intermod to crazy
levels as observed before. This time I swapped the RX rig to the TS-440
and the intermod for the most part disappeared. Putting the big
vertical on the FT-897D resulted in good signals from the 'warbler'
without intermod at all anywhere within the narrow window of the high Q
system...
Summary of results:
* Seems the intermod is mostly generated in the FT-897D as suggested
by some. Therefore, I wouldn't recommend the use of a Miniwhip(or
perhaps other active whips) and 897 to someone in an RF wasteland
like mine.
* Height and location in the yard greatly affect the performance of
the miniwhip and appear to make or break its performance.
* The miniwhip collects more noise then the vertical. Different
isolation methods do help but generally it appears to soak up more
local noise, maybe more DX signal too ;-)
I'm a believer. Nice work Roelof!
73 Scott
PS - I hope to update the TIL grabber tonight to simultaneously post
both miniwhip and 'big' vertical grabs from here.
Roelof Bakker wrote:
Hello Scott,
I am living in a suburban area, with plenty of electronic equipment in
full swing.
However, all cabling is underground.
I have some interference from my own VCR on certain parts of the band
which is propagated by the TV cable system running underground
practically onder my mini-whip.
I have had reports from people with power lines in the vicinity.
Raising the antenna above the level of the power lines did help.
73 Roelof Bakker, pa0rdt
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