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Author Topic: SWL antenna  (Read 6135 times)
WB4SPT
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Posts: 308




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« on: November 15, 2015, 02:10:25 PM »

I just picked up a SPR4 and am thinking of a Rx only antenna to feed it to a second story bedroom.  I have some 50 ft tall trees around so there are some options for an outside wire antenna.  Given that the antenna would be about 25 feet high, there is an option to do a 75' end fed, or a 75' dipole.  This radio is 50 ohm  for > 2MHz and hi-Z for <2MHz.  Obviously, this wont be a matched antenna system, but is there any merit in using a dipole over a long wire, the length being equal?  I don't have any particular bands that I'm partial to, but MW broadcast, 40 meters and 17 meters would be great. 
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WW7KE
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Posts: 340




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« Reply #1 on: November 15, 2015, 06:10:45 PM »

If the HF input is 50 ohms, a tuner will be required for a wire antenna on most frequencies other than those where the wire is a 1/4 or 3/4 wavelength long.  A simple L-network should suffice.  A single- or double-screw connector like the classic general coverage receivers had only required the built-in "Antenna Trimmer."
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KD7RDZI2
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Posts: 115




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« Reply #2 on: November 16, 2015, 12:36:39 PM »

First congratulations for your new receiver!!! I never had a SPR4, hope to find one somewhere in the future. According to http://www.universal-radio.com/catalog/commrxvr/spr4.html the antenna input is 50ohms and there is a preselector. I think it would be quite difficult to tune both an external tuner and the preselector. I would rather use a 9:1, 12:1 or 18:1 unun and at least 12m longwire. With this setup I think would be easier to tune the preselector.

As you have a garden, hence a good ground, I would experiment with a low cost active antenna such as http://www.ebay.com/itm/Mini-Whip-active-antenna-kit-10kHz-to-30MHz-160-to-10-meter-bands-/121811260969?hash=item1c5c845629:g:LAQAAOSwjVVVhGlS. This kind of antenna need a good ground and can be mounted close to the ground.
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K1DA
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Posts: 689




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« Reply #3 on: November 16, 2015, 04:56:21 PM »

Don't transmit on HF with another antenna with the Drake connected to whatever you put up for it. 
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K0OD
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Posts: 2781




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« Reply #4 on: November 16, 2015, 05:43:48 PM »

Run a random long hunk of wire to a tree. 75' is good. You can compensate for inevitable mismatches ... by turning up the audio gain a bit.  Simple, eh?
« Last Edit: November 16, 2015, 05:48:28 PM by K0OD » Logged
WB4SPT
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Posts: 308




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« Reply #5 on: November 16, 2015, 06:36:09 PM »

Don't transmit on HF with another antenna with the Drake connected to whatever you put up for it. 

Risk of FET damage?   It does have dual diode input protection built in.  i think I read of a 30V RF rating on the front end.  But, yes, I do xmit with 1kw using different Drake equipment and a different dipole that will be only 30 feet from the new SW antenna.   Likely the new SWL antenna will be a sloper, rising to some 40 feet towards a locus tree. 
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ZL2MC
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Posts: 20




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« Reply #6 on: November 21, 2015, 02:35:35 PM »

I can thoroughly recommend an OCFD also known as a 'Carolina Windom'. 20metres (66ft) one side, 10metres the other (33ft) with a 9:1 transformer (un-un) at the 'centre' and 50ohm coax to your receiver. Performance falls of below 2MHz and above 20MHz but that doesn't worry me as I don't need to listen the the BC band or the Clowns Band. I can hear a little 500watt station in South America on 5940kHz on the Grey Line every evening.

https://soundcloud.com/majoco21/radio-voz-missionara-5940khz17oct

Cheers - Martin ZL2MC Palmerston North, New Zealand.

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