Hi Ian,
I think I'd be taking a close look at both transmitters with a spectrum
analyser and seeing if they are both suitable for repeater work. I'm not
familiar with either radio, but usually radios designed for duplex work go to a
lot more trouble with internal shielding than your average
Jess,
Tape an empty aluminium drink can to the side of the single point earth strap
(or to the leg of the tower).
The magnetic field from the few thousand amps of strike current should flatten
the drink can in microseconds!
Mark vk3byy
From:
This is already happening in Australia. Amateurs are secondary users for
420-450MHz, with military and radio location being primary.
A few years ago our ACMA introduced Low Interference Potential Devices
license class (any modulation, for any purpose, 25 mW maximum, no license
required).
I would have thought good grounding practices on the feeder and equipment at
the base of the tower would have pretty well bypassed any 1.25MHz stuff.
Ferrite 'beads' will reduce common mode pickup on coaxial cables without any
effect at all on the signal inside the coax.
Don't expect too much
Hi Tony,
Are you using a duplexer on this repeater?
A lot of cavity filters act as a short circuit to DC and low frequencies, so
additional filtering is unlikely to help.
I can only think of one type of cavity that has a DC path between from input to
output (via an internal inductor) and not to
I know of one amateur repeater where a distant AM broadcast signal mixed
with a commercial Tx operating on the same tower to produce interference on
the repeater input.
The problem was tracked to a rust joint between the galvanised iron roof and
the guttering of the equipment hut.
The broadcast
to measure a 60dB notch, but you can at
least measure individual cavities.
Mark Harrison
VK3BYY
-Original Message-
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Azam
Sent: Wednesday, December 23, 2009 8:20 AM
To: Repeater-Builder
Here in Australia all the digital stations are somewhat lower power than
the analogs, so as far as interference to your receivers goes, that may
be a saving grace.
I would imagine that if you live near a TV station that your front ends
will need to have pretty good on intermod performance (I don't
Yes, SWR is a problem for long power distribution lines, but only the very
long ones.
There was a case I think in Canada where they ran into this problem. The
transmission lines from one side of the continent to the other was an odd
multiple of a quarterwave (1,250 km). Since a quarterwave acts
Hi Eric,
I agree with most of what you say, except the bit about generators and
horsepower.
I've always understood poor power factor to be a problem because the
generator and distribution system needs to carry higher currents to deliver
the same energy into a poor load. That's a problem because
Ooops - typo - should have written 1.250 KVA, not 1250KVA as that would mean
1.250 MegaVA !
Mark
-Original Message-
From: Mark Harrison [mailto:[EMAIL PROTECTED]
Sent: Wednesday, 17 September 2008 2:54 PM
To: 'Repeater-Builder@yahoogroups.com'
Subject: RE: [Repeater-Builder] Volt-Amp
Hi John,
I'm not familiar with that particular radio, but would it be possible to
disconnect the antenna feed at the Rx PCB and place a 50 ohm surface mount
resistor in it's place?
That may allow you to differentiate between shielding problems in the
receive antenna cabling and other possible
For a better pickup loop, solder a 50 ohm surface mount resistor in series
with the loop at the end of the coax, and put a few ferrite RFI beads or
clamps at random distances along the coax. This reduces pickup by the coax
itself which can otherwise cause misleading measurements.
Since the loop
Subject: [Repeater-Builder] Re: Interference on a 6 meter repeater
Mark Harrison [EMAIL PROTECTED] wrote:
Hi Skipp and Joe,
BTW, You could also use a lower gain antenna instead of a power
attenuator. High gain antennas are not always a good idea :-)
73,
Mark vk3byy
In 97.5% plus
Hi Skip and Joe,
Yes, placing attenuators in line can tell you a lot about IM and
interference problems.
In Joe's case it would be interesting to know if placing an attenuator
in the antenna line (assuming a shared receive/transmit antenna)
produces an equivalent reduction in the NOAA signal, or
Hi Joe,
That's odd that the cavity in the telemetry radio feed didn't change
things, but it goes away when the radio is disconnected from the
antenna.
A third condition to try would be with the cavity connected to antenna
but leave radio disconnected. If the IM is still present then I'd be
Hi Wayne,
From memory the suggestion was to use 50 ohm double screened cable for
the phasing harness and intercavity cables.
RG-142 (not to be confused with the far more popular RG-214) has two
layers of braid and there are other types from various other
manufacturers.
You may be able to pick up
17 matches
Mail list logo
