You might try winding the coax lead between the tuner and the rig into an
RF choke. You might also, try hanging some counterpoise wires off the chassis
of the tuner (1/4 wavelength on the band of interest). If RF is coming in
on the power lead, try winding it into a choke also (a ferrite core might be
if you have any available). The main idea is to create a low pass filter for
mode RF currents so that they are shunted away from the rig (the choke creates
a high series impedance toward the rig while the counterpoise radials
creates a low shunt impedance away from the rig).
----- Original Message -----
From: "Eric Scace" <email@example.com>
To: "Towertalk" <firstname.lastname@example.org>
Sent: Wednesday, March 21, 2001 9:29 PM
Subject: [TowerTalk] FW: RFI suppression
> -----Original Message-----
> From: Eric Scace [mailto:email@example.com]
> Sent: 2001 March 20 Tue 11:54
> To: Towertalk
> Subject: RFI suppression
> Hello everyone --
> I'm sure this problem has been solved effectively before. I'm looking for
> suggestions for effective techniques.
> 1., When transmitting, RF disrupts my computer-to-radio keying systems.
> 2. On some frequencies RF appears to be causing problems in the transceiver
> a) The final stage's forward and reverse power detectors will, on some
> frequencies, report irregular values. These values are
> not consistent with a conventional Daiwa dual-needle SWR meter installed
> immediately adjacent to the transmitter's output
> b) The transmitter's internally generated sidetone occasional shifts
> frequency at the start of keying.
> -- My station is on the 6th floor of a 6-floor apartment block.
> -- My antenna is a vertical dipole, cut for 7.15 MHz, and fed by an antenna
> tuner to force it to accept RF on 80m thru 10m. The
> feedline is coax. There is no balun at the antenna feedpoint.
> -- There is no safety ground in the local power system in this building. 220
> VAC is provided as a pair of wires.
> -- I can not bring an earth ground into the apartment from outside. The
> apartment overlooks the grounds of the French embassy,
> which I can't enter. In any event, a 20m long "ground lead" will certainly
> be floating by the time it enters the apartment.
> -- I suspect the coax between the antenna and tuner is hot with RF on its
> -- Since the chassis of the tuner can not be earthed, it's likely that the
> coax between the tuner and transceiver is also hot with
> Your ideas?
> Eric R3/K3NA
> PGP fingerprint: F40B A402 795B 3F52 43B0 47B4 3576 BA88 3A34 5058
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