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Author Topic: Tabletop receiver antenna  (Read 11760 times)
KE7RNK
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Posts: 9




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« on: March 10, 2013, 08:34:26 PM »

Recently purchased a new Icom IC R75  receiver, and want the best antenna for it . For best results should I go long wire(insulated or not,length,gague), get a shortwave antenna (dipole or verticle), or get a quality ham antenna. Thanks for your feedback,
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KB8VIV
Member

Posts: 47




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« Reply #1 on: March 11, 2013, 07:18:48 AM »

Well, I use my full wave 80 meter horizontal loop (up only 25 ft) for swl'ing and hamming on 10 - 80 meters.  As you can imagine it excells on the lower bands, it's a great multi-band antenna.  There are lots of other really great options that I have no experience with.  If you want to see how it works you can check my qrz logbook and some of my swl and dx contacts on youtube under 'Desmoface.'

73's es good luck.
de kb8viv
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K5TED
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Posts: 676




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« Reply #2 on: March 11, 2013, 10:17:54 AM »

K0OD provided a very informative link in the "Active vs. Passive Antennas for HF SWL " thread.

IMO, you should have a variety of antennas in your arsenal.
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AD4U
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Posts: 2150




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« Reply #3 on: March 11, 2013, 11:33:39 AM »

For starters install a wire as long and as high as physically possible.  The wire gauge and insulated or not does not matter.

Dick  AD4U
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K1DA
Member

Posts: 460




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« Reply #4 on: March 19, 2013, 09:46:33 AM »

Yoyu bought a god receiver, now you need to put up a longwire antenna of some random length and pick up a used, simple, tuner with "longwire" input.  Just about any of the small MFJ tuners will do, (despite all the jokes about the company).
What you will find is the "good receivers" like ther Icom, alike to see 50 ohms (except for the "lowband" wire input which is for 500 KMZ and below, and a little tuner will  make the wire :look like" 50 ohms to the receiver 50 ohm input.  Easy to use, just crank the dials and look for the strongest signal level. 
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K5TED
Member

Posts: 676




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« Reply #5 on: March 19, 2013, 06:43:29 PM »

If you are planning to use a long wire for SWL, invest in a preselector..

A preselector is a radio technological term for an electronic device that is inserted between the antenna and the receiver, limiting the range of frequencies that can be applied to it. Tuning to the desired frequency keeps the preselector's narrow bandwidth centered at the operating frequency, rejecting or reducing out-of-band unwanted interference signals. A preselector also protects the sensitive receiver input from damage caused by static and voltage transient. It improves the performance of nearly any receiver, but is especially helpful to those with broadband front-ends that are prone to overload, such as scanners or average receivers.
 
Extra filtering is needed because the front of the receivers, conformed by the RF power amplifiers and mixer, have a limited dynamic range. Dynamic range is defined as the amount of RF energy those circuits can handle without overloading. If the front-end overloads, the performance of the receiver is severely reduced or even damaged. In situations with noisy and crowded bands, or where there are strong local stations, the dynamic range of the receiver can quickly be exceeded. Extra filtering limits frequency and power that are applied to the receiver, allowing them to handle the overall dynamic range of signals that are within the desired band.
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K0OD
Member

Posts: 2520




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« Reply #6 on: March 19, 2013, 08:03:39 PM »

Learn something new everyday: "[preselector] improves the performance of nearly any receiver,..."

Shouldn't you properly attribute that ineloquent blurb to Wikipedia, where you copied it from?

Also: "This article may require cleanup to meet Wikipedia's quality standards." Cleanup is right! Plus no author is cited. He's probably in the preselector business.

http://en.wikipedia.org/wiki/Preselector

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K5TED
Member

Posts: 676




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« Reply #7 on: March 19, 2013, 08:14:36 PM »

As the authority here, you should educate us as to why the preselector industry has thrived for a century, and also, more importantly, why exactly preselectors are absolutely ineffective.

Also, please explain why thousands of radio hobbyists are wrong in perceiving an improved usability and enjoyment of their hobby when incorporating a preselector.

Also, please explain how a receiver with a wideband front end might not benefit from the incorporation of a preselector.


I'm waiting for your sage instruction...

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K5TED
Member

Posts: 676




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« Reply #8 on: March 19, 2013, 08:18:20 PM »

Learn something new everyday: "[preselector] improves the performance of nearly any receiver,..."

Shouldn't you properly attribute that ineloquent blurb to Wikipedia, where you copied it from?

Also: "This article may require cleanup to meet Wikipedia's quality standards." Cleanup is right! Plus no author is cited. He's probably in the preselector business.

http://en.wikipedia.org/wiki/Preselector



While you're at it, how about refuting the Wiki statements with facts? Let's hear it. How's that antenna business going?

Got any government sales? We all know the federal government routinely pays thousands of dollars for commode seats.. Wonder what they pay for special antennas?
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K0OD
Member

Posts: 2520




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« Reply #9 on: March 19, 2013, 09:31:50 PM »

Long ago, when I was about 14 years old, I picked up a used Millen preselector like the one shown below. It helped neither my National NC-88 (which dearly needed help) nor my Collins 75A2. 

Most 1940/50s ham receivers were deaf on 10 meters and the new 15 meter band. So preselectors sold well to the hobby's arriving hordes of wet-behind-the-ears "space cadets." 
 
http://www.isquare.com/personal_pages/millenpreamp.htm

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K5TED
Member

Posts: 676




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« Reply #10 on: March 19, 2013, 10:06:12 PM »

Long ago, when I was about 14 years old, I picked up a used Millen preselector like the one shown below. It helped neither my National NC-88 (which dearly needed help) nor my Collins 75A2. 

Most 1940/50s ham receivers were deaf on 10 meters and the new 15 meter band. So preselectors sold well to the hobby's arriving hordes of wet-behind-the-ears "space cadets." 
 
http://www.isquare.com/personal_pages/millenpreamp.htm



Anecdotal.

here, I can do that too..

On a PCR-100 with 455kHz tap and random wire antenna, I get much better DReaM DRM decode putting a MFJ 945E in line and tuning for max signal. The A/B comparison after tuning supports this.

In essence, for this exercise, that particular radio is indeed performing better for the task at hand with a preselector than without. That's what this discussion is about, unless I've read the OP incorrectly.

So, our respective anecdotal evidence is at odds.... Who's right? I'd venture that your venerable old NC-88 was possibly irretrievably broken, and the Collins might have been in need of a more sage hand... Maybe that tube amplified preselector had a very high noise figure.  I prefer a passive preselector.

Seriously, there are plenty of readers here looking for real world answers, and a very few others looking for math. And let's not forget the aging space cadets..

I can only pass along what I've learned through my own experiences.



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KB4QAA
Member

Posts: 2236




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« Reply #11 on: March 19, 2013, 11:36:35 PM »

I don't think the average, or even expert, SWL'er needs a preselector, except in special circumstances.

A preselector can be helpful in situations with strong signals, and adjacent band signals, such as military comm sites (or Field Day), by acting as a bandpass filter against  the interfering signals.
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