What Exactly is 'Overload' on my Receiver?

MikeThompson

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I've hooked up 100ft of speaker wire antenna to my old Grundig to get my feet wet in the hobby. I am starting to look at more modern (at least newer than my Grundig) shortwave receivers. I'd like something with SSB and a larger frequency range. Anyway, I've heard that a longer antenna might 'overload' portable receivers.

What does that mean exactly? I'm picturing some sort of cartoonish explosion of the radio. Is it just something internal on the radio that pops?
 

rrbum

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mmckenna

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What does that mean exactly? I'm picturing some sort of cartoonish explosion of the radio. Is it just something internal on the radio that pops?
In very generalized terms, think of it as being at a party and having a quiet conversation with a nice young lady. Meantime the drunk football player is screaming loudly in your ear.

Trying to listen to weak stations, say a shortwave station from halfway around the world, while the loudmouth politically bent AM talk radio transmitter a few miles away running 50,000 watts is doing the screaming. Even though it's not on the same frequency, it saturates your radio. Too much antenna sucking in all that RF and not sufficient filtering on the radio to keep out the stuff you don't want to hear.

Again, simplified terms.
 

WA8ZTZ

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Generally it takes a strong local signal to overload a receiver. However, overload can also happen with the use of an active
antenna running wide open. There is such a thing as too much gain. There are many types of interference but typically
receiver overload will cause the desired signal to sound distorted or in a really bad case you may hear just dead air.
A 100' antenna connected to the antenna jack (not the whip) on your portable is probably not going to overload the receiver.
 

ridgescan

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Generally it takes a strong local signal to overload a receiver. However, overload can also happen with the use of an active
antenna running wide open. There is such a thing as too much gain. There are many types of interference but typically
receiver overload will cause the desired signal to sound distorted or in a really bad case you may hear just dead air.
A 100' antenna connected to the antenna jack (not the whip) on your portable is probably not going to overload the receiver.
This! Even my cutting-edge Icom R8600 gets overload in MW. If I'm trying to listen to 580kHz KMJ Fresno at 160 miles, I need to give it at least 20dB attenuation as I'm so close to at least three MW flamers here in San Francisco.
Classic overload right there.
 

DeepBlue

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This also happens imperceptibly in this situation... the radio is tuned to a nice station, just down the band is another station at a super high power. You haven't got that station tuned in but it is so strong and in the passband of the radio that your radio may be suhutting down the receive to compensate for the strong signal just out of range of where you are tuned. This is actually something a bit different but related. It is a form of overload. You can sometimes abate this condition by using a receive variable passband filter between you and the antenna. You have to effectivly tune 2 different devices however to make it work correctly. It's actually called a Passive Preselector. This would probably help on SW if you have "out of band" strong stations near you. Something like this:

S
 

eorange

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Has anyone used the MFJ-1046 or the prior 1045? Most reviews I've read indicates it doesn't really do anything.
 

DeepBlue

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Has anyone used the MFJ-1046 or the prior 1045? Most reviews I've read indicates it doesn't really do anything.
The passive versions I have had come across my desk have worked fine. I am not crazy about amplified devices as they tend to create more issues than they solve. The reduction or "insertion loss" isn't that high to worry about for me where I live with my radios and antennas. There are many such passive filters. You can also look at other companies offerings, and should.

Alsoi, Google can be a pal in the search for answers on this topic:

Etc.

S
 

MikeThompson

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think of it as being at a party and having a quiet conversation with a nice young lady. Meantime the drunk football player is screaming loudly in your ear.
Language I can understand! Thanks!

A 100' antenna connected to the antenna jack (not the whip) on your portable is probably not going to overload the receiver.
Good to hear. I'm thinking about upgrading my receiver but would still like to use my wire antenna setup as an external antenna to plug into the receiver.
 

Scan125

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I use a simple external wire antenna and it is fine for LF/MF/HF (up to 130MHz as it quite happily picks up aircraft).

You mentioned the MFJ-1046. I have an MFJ-956 and find that it is very useful and tuning/selecting weaker signals. I also have a MFJ-959C which is also good but the big advantage of the 959 is that it has two switch-able inputs (ANTenna 1 and ANT2) and two switch-able outputs (ReCeiVeR1 and RCVR2). The design is such that you only need to power the unit if you want the internal amp for signal boosting. The tuning and Attenuator functions all work with no power.

If you only ever plan to have the one antenna and once receiver then the MFJ-956 is the one to go for. It is cheaper, smaller and easier to use. Just set your desired band and twiddle the tune knob.

A point to note about both units (and similar other makes) is that they are not miracle devices. Often they appear to do nothing. My default setting for both units is BYPASS (i.e. do nothing). Only when a faint signal or a signal in out of band noise is difficult to listen to do I then bring the tuners/pre-selectors into play. This is how I use mine but other may adopt a different approach.

One reason you may want two antennas is if there are more local powerful radio stations that you like to listen to and your long wire is just too receptive. Then a small in house telescopic/short wire would be useful. Will all depend on your location and listening requirements.
 

spongella

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If your receiver has an RF gain control you can adjust it to prevent/control overload but many receivers don't have them.
 

Boombox

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Overload is a big deal, and then it isn't. Radios that will overload with longer antennas usually work well with shorter ones. Most of the overload I've had with my own radios is either FM station hash above 12 Mhz (infrequent) and strong SW broadcast stations also appearing in wrong places in the SW spectrum (where the utility stations are). So YMMV, depending on your location, the radio you use, your antenna, and how close you are to strong AM stations.
 
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