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LF: Re: Re: T/A May 14

To: <[email protected]>
Subject: LF: Re: Re: T/A May 14
From: "Roelof Bakker" <[email protected]>
Date: Mon, 15 May 2006 19:21:27 +0200
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Hello Dave,

Yes, I will be using a BFR96 solely for being better adapted to SMD mounting. So far I have had no problems in sourcing 2N5109's in the Netherlands. They are still widely available in Europe.
Regarding your remarks on the feedline contributing to reception; that gives
rise to an interesting question. I have only used non metallic poles with my
mini-whips, because they were available and much easier to handle. However,
I received a few questions on the use of metalic poles. Someone told me that
an active whip will stop working when the coaxial feedline is tied to a
metal pole or runs inside.
I have performed a few tests on a short ( 4 feet high) metal and fiberglass
pole. I have used groundwave signals from DCF39, 138.830 kHz, 575 km and
the carrier of NDB ONO-399.5, Oostende, Belgium, 399.500 kHz, 59 km.
Test # 1, metal pole, coax cable taped to the pole.
DCF 39: -74 dBm
ONO-399.5: -79 dBm

Test # 2, metal pole, coax cable extended horizontal, 4 feet high
DCF 39: -64,5 dBm
ONO-399.5: -72 dBm

Test # 3, fiberglass pole
DCF 39: -55 dBm
ONO-399.5: -69 dBm

Test # 4, fiberglass pole, shield of the coax cable grounded at the bottom of the mast
(copper earth stake, 3 metre long)
DCF 39: -51,5 dBm
ONO-399.5: -71 dBm

Received on a SPM-30 and a 20 dB tuneable pre-amplifier.

The differences in signal strength between a conductive and a non-conductive mast are large; at 138.830 kHz 19 dB and at 399.5 kHz 10 dB. Thus, it seems to be good practice to use a non-conductive mast.
Test # 4 is interesting. Connecting the shield of the cable at the bottom of
the mast, gives a 3.5 dB stronger signal at 138.830 kHz. However, at 399.5
kHz the signal level is 2 dB less.
I have not a simple answer for what is going on here. From the bottom of the
mast to the house the feedline is 11 metre long. The shield is connected to
a groundstake somewhere in between and before entering the house. Inside the
house the coaxial cable is 6 metre long. To simplify matters, I will repeat
these tests with my battery operated SPM-3 and a short length of coax.
Best regards,

Roelof Bakker, pa0rdt

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