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| 2m Wire Slim Jim |
connected to the BNC using the same wire. Water ingress points were sealed off with 'Araldite'.
An SWR of 1.5:1 was realized.
Related post: 2m J-Poles and a Slim Jim
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'Wire Slim Jim' for 2m
This is a 'Wire Outside PVC' Slim Jim for 2m. It was made using enamelled copper wire and a vacuum cleaner nozzzle!
The wire ends and the BNC connector were fixed with self-tapping screws. The feed points were
connected to the BNC using the same wire. Water ingress points were sealed off with 'Araldite'.
An SWR of 1.5:1 was realized.
Related post: 2m J-Poles and a Slim Jim
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connected to the BNC using the same wire. Water ingress points were sealed off with 'Araldite'.
An SWR of 1.5:1 was realized.
Related post: 2m J-Poles and a Slim Jim
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2m J-Poles and a Slim Jim
Last summer an attempt was made to homebrew a couple of 2m antennas, using parts salvaged from a disused VHF TV Yagi Beam.
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| 2m J-poles and a Slim Jim |
The moulded plastic box was used for the second version of the J-Pole. For the stub portion, the 2 elements were shorted inside the box. A BNC connector was located at the lower end of the box. A length of PVC pipe was fastened to the box to facilitate mounting of the antenna.
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| Close-up of the J-poles |
'M-Seal’(epoxy sealant in dual component lump form) was used at the joints and to waterproof the connections.
The dimensions were arrived at using 'K4ABT's J-Pole Calculator'.
Absolutely no trials / adjustments were required to get the SWR very close to 1:1!
Absolutely no trials / adjustments were required to get the SWR very close to 1:1!
With the remaining material a Slim Jim came into being.
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UHF on a VHF Rig
This circuit enables fair copy of strong 444 MHz signals, off a local repeater, using a 2m rig and an indoor 70cm ¼λ ground plane antenna.
The 300 MHz 5th harmonic of the local oscillator, mixing with the incoming signal, delivers output on 144 MHz.
The enclosure is a plastic trinket box reworked to fit two BNC sockets plus one RCA for the DC supply and also to screw the cover in place.
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| UHF Converter |
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| UHF Converter - Schematic |
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| UHF Converter - inside view |
The converse (VHF on a UHF Rig) is also possible by just changing over to a 2m antenna and a 70cm rig.
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A ¼ λ Ground Plane for 70 cm
It is easy to homebrew this ¼ λ ground plane antenna for 70cm. All one needs is a TNC connector (see inset), 1.6mm brass brazing rod and a pack of ‘M-Seal’(epoxy sealant in dual component lump form).
Radiating element length in inches is 2808/f MHz minus the projecting length of the TNC hot end.
Radial length in inches is 2950/f MHz plus a little for soldering on to the TNC connector flange.
The soldered points are sealed against water ingress using M-Seal.
Related post: Coax Collinear for 70 cm
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| ¼ λ Ground Plane for 70 cm |
Radial length in inches is 2950/f MHz plus a little for soldering on to the TNC connector flange.
The soldered points are sealed against water ingress using M-Seal.
Related post: Coax Collinear for 70 cm
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Fox Hunt Attenuator
Here's the circuit of my homebrew fox hunt attenuator.
It's a simple offset attenuator with a low part count.
The potentiometer is used to vary the signal strength of the attenuated signal, available at +1MHz, +2MHz, -1MHz, -2MHz of the fox frequency.
This attenuator was successsfully employed at a couple of fox hunts in Bangalore.
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| Offset Attenuator - Schematic |
The potentiometer is used to vary the signal strength of the attenuated signal, available at +1MHz, +2MHz, -1MHz, -2MHz of the fox frequency.
This attenuator was successsfully employed at a couple of fox hunts in Bangalore.
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Coupling a commercial VHF handheld to an external antenna
Some good commercial VHF handhelds have only one drawback - no external antenna connector.
Modification is also a problem as the rubber ducky is either integral or screwed on to a threaded stud, with no access to ground.
The result is a frustrated, repeater-bound ham. When a fellow ham in such a predicament set me pondering, realisation dawned that another rubber ducky could be used to couple the rig to an external antenna.
My own rig (which has a BNC connector!) was used to check it out. The coupling rubber ducky was mounted on the input of a homebrew SWR meter, with a dial lamp loading the output.
Modification is also a problem as the rubber ducky is either integral or screwed on to a threaded stud, with no access to ground.
The result is a frustrated, repeater-bound ham. When a fellow ham in such a predicament set me pondering, realisation dawned that another rubber ducky could be used to couple the rig to an external antenna.
My own rig (which has a BNC connector!) was used to check it out. The coupling rubber ducky was mounted on the input of a homebrew SWR meter, with a dial lamp loading the output.
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| Rubber ducky coupling to a dial lamp |
The glow of the dial lamp indicated a coupling efficiency of about 20% (2.5W to 0.5W).
A 2m external antenna was then connected instead of the dial lamp.
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| Rubber ducky coupling to an external antenna |
On-the-air tests were successful. Comfortable simplex QSOs, not possible with the rubber ducky alone, were now possible.
Related post: SWR Meter - Easymatch
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Handy 1 kW HF Dummy Load
Years ago, after replacing the tubes of a Heathkit SB-200 Linear Amplifier, I was on the lookout for a dummy load to test it.
The amplifier was successfully tested, with its Pi tank circuit providing a proper match to the dummy load.
At a later date, the same exercise was repeated with a Dentron GLA-1000.
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It then struck me that a 230V ~ 1kW electric hot plate, with its heating element resistance close to 50Ω, would do.
The mains plug of the hot plate was replaced with a PL-259 before connecting it to the output of the linear amplifier.
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| Handy 1 kW HF Dummy Load |
The amplifier was successfully tested, with its Pi tank circuit providing a proper match to the dummy load.
At a later date, the same exercise was repeated with a Dentron GLA-1000.
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