|
|
Re: Re: Improve your HF reception with the LOWE PR-150 Pre-Selector: msg#00063
recreation.radio.hardware.icom.pcr1000
|
Subject: |
Re: Re: Improve your HF reception with the LOWE PR-150 Pre-Selector |
Arcticpeak wrote:
This is correct, it is one of the drawbacks by using a
pre-selector, but I never scan on HF any way, and the bandwith of the
preselector is not so narrow for tuning in the same band. Actually it
ain't much hasle with it at all, and the improvement in reception is so
large, that the ekstra effort is well worth it. And of course you can
bypass the pre-selctor at any time it suits you, just by pushing a
single button.
Martin
The bandwidth and Q of the filter has a lot to do with the antenna
impedance.
Some common tuner settings, and frequency, 7.1MHz:
28pF, 13 uH, SeriesR=801 ohms, 7.09MHz
500 Ohms from a longwire 50 Ohms 5 Ohms from Antenna
tuner using matching transformers
Bandwidth 4.4 MHz 442KHz 44KHz
Q= 1.6 16
160
Now, the BCC preselector uses a matching transformer that takes the 50
ohms from a proper
antenna and brings it down to around 5 Ohms, yielding 'ten times'
better filtering action...
http://www.bavarian-contest-club.de/projects/presel/presel.pdf
The other thing I noted was with what happened if I decided to tune
the same frequency
using other bandselect positions:
103pf, 4.9 uH, Series R=218, 7.08 MHz
500 Ohms 50 Ohms 5 Ohms
Bandwidth 16 MHz 1.6MHz 162KHz
Q= .44 4.4
44
And finally;
180pF, 2.8uH, SeriesR=124Ohms 7.09MHz
Bandwidth 28 MHz 2.8MHz .284KHz
Q= .25 2.5
24
So, as you can see, the antenna really sets up the pre-selector. And
hooking a piece
of wire to a piece of coax isn't going to tune much. I'd guess the
stock PCR antenna
is 600 Ohms at 30 MHz, and 6000 Ohms at 3 MHz so putting that on a
tuner won't
preselect anything.
One product that will help match your longwire AND HELP PREVENT STATIC
DISCHARGES (pre-strike charged clouds) is a Longwire Balun.
By mounting this near a GOOD ground, this will provide a discharge
path OUTSIDE
your radio, and help ground your coax so the shield doesn't become an
antenna.
Third, it also lowers the antenna impedance by factor of ten. And we
know how
that helps the tuner.
http://www.grove-ent.com/WR0130.html
http://www.palomar-engineers.com/MLB-1/mlb-1.html
My next idea is to replace TR2 on the BCC project with a simple 1 FET
impedance transformer. Perhaps 5 Ohms is a bit low for a FET, but one
that
converts 5000 Ohms (PCR antenna) to 50 Ohms would help?
Good luck, and try the other band options and report back, Thanks!
Skip Flem, NT1G
Hull, Massachusetts
So
everytime you tune away a bit on the pcr1000 you have to manually
tune the preselector as well? You can no longer do search or scan?
I guess that's why it is not used that much by the SW listeners?
Ubbe.
Arcticpeak wrote:
>
> Recently I bought a used LOWE PR-150 Pre-Selector from a friend
Yahoo! Groups Links
|
|
|
