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Author Topic: Best HF receiver with lowest noise floor  (Read 24945 times)

Posts: 2

« on: December 25, 2016, 11:58:46 PM »

Hi, there is a lot of RF noise where I live (even with the power turned off!) so I am looking for any radio (receiver or transceiver) that could possibly be the best at hearing weak HF signals with a very low noise floor. I used to have a Ten Tec RX 340 but it was too noisy. Thinking about the AOR 7030, but I thought I'd post here to see what suggestions I might get. Thanks!

Oh also, the antenna I'm using is a magnetic loop (can't put one outside).
« Last Edit: December 26, 2016, 12:17:36 AM by KB1VNC » Logged

Posts: 554

« Reply #1 on: December 26, 2016, 03:28:17 AM »

 Welcome to the forum. What receiver are you using presently? It is always preferable to stop the noise at its source than to attempt a 'clean-up' at the receiver end.
 Much depends on the type of noise that you are trying to subdue. (See the eham RFI/EMI forum for additional tips). Rule out local noises in your own living space before asking neighbors within 20m for their help.
 The AOR is a fine receiver, but I won't say that it will fix the problem. An SDR/DSP receiver might help cut noise also.
 I long suspected the neighbors as being the problem until I took a second look at what I had powered on. I  found a noisy florescent lamp in the basement, reversed AC outlet wiring in part of the house (unsafe) and switching router/computer power supplies that sent noise across the AM band. There was a buzz every half turn of the tuning knob.
 I replaced the defective lamp and repaired the house wiring. I can turn off and unplug the computer and I installed an old-school 12 volt linear power supply, disabling the switching 15 volt supply for the router. The router runs the telephone service, so I have to keep it on.
 The AM band is now quiet. I can listen to my distant, low-power 850 kHz music station during the day and AM-DX in the evenings again. Noise on the SW bands wasn't as bad and it got better in the higher frequencies.
 I found that most of my noise generators were within 8m of my receiver and attic longwire.

Posts: 673

« Reply #2 on: December 26, 2016, 09:24:30 PM »


Radio is only a small fraction of the equation and the largest reduction in noise comes from proper selection and installation of an antenna.

SDR radios are a good place or more expensive IF DSP radios if you want superhet. Also consider an outboard DSP unit like the West Mountain CLRDSP or the Timewave DSP units.

Posts: 2

« Reply #3 on: December 26, 2016, 11:36:48 PM »

I live in an apartment building, I can't put up an outdoor antenna so I use the magnetic loop designed by KR1ST.

I had a Ten Tec RX 340 but it was too noisy. Although not much noisier than videos I have watched of that radio.

I have seen videos of other radios, though, that seem to be capable of being very very quiet. And according to this chart here:

it would seem that this is not entirely in my head, as many of the radios there are rated as having a lower noise floor than the 340, and some are also more sensitive.

Maybe if I got a Collins 75-S3B with that Timewave DSP you mentioned, maybe that would do the trick?

Right now I'm not using much for a receiver, but I am looking to get one if I think I can pull in really tough catches, for instance, is it within the realm of probability to hear low-power stations from Southeast Asia from East Coast USA? Or is that just not going to happen in an apartment?

I have tried shutting off the power entirely in my apartment and using a battery-powered radio. Still noisy.

Posts: 331

« Reply #4 on: December 27, 2016, 06:42:30 AM »

At HF the problem isn't the noise figure of the receiver, it's the ambient (external) noise that limits your ability to copy very weak signals.
Using DSP will mitigate some of the noise, how well depends on the sophistication of the DSP algorithm and the processor behind it.
You might try one of the noise cancelling devices on the market. These are essentially a second receiver and antenna that introduce the noise at the primary receiver input, but at 180 degree phase shift, cancelling out the noise.
Being that you're in an apartment, you could be "Signal Limited". In other words, the apartment is representative of a Faraday cage, so signals are being prevented from reaching your antenna in the first place.
If you can open a window, you might try dropping a random length small diameter (such as magnet wire) wire outside during your listening times. It's not ideal, but it would be stealthy and probably work much better than an indoor antenna.

Good Luck
By 73
You indicate wanting to copy signals from many thousands of miles away. Propagation will have a lot to do with that. I'm assuming that you're taking this into account.

Posts: 1728

« Reply #5 on: December 27, 2016, 07:22:15 AM »

Yes, the noise floor of your location is much higher than probably even a cheap all band radio, so reducing the noise floor of your RX is not going to help. I feel your pain, but I doubt there's much you can do about it without getting an outside antenna somehow. Consider mobile HF operations. That's what I did once when I was limited that way.

Posts: 51

« Reply #6 on: December 27, 2016, 11:55:13 AM »

Hi with out a decent antenna you are not going to get any where regardless what receiver you have main intrest for me is monitoring hf aircraft world wide got lots of receivers did also have 4 wellbrook active loops worked okay but since i got my pk loops dipole wire antenna they do an excellent job the loops dont get used any more sold 2 of them with no regret as for sdr had the commradio cr-1,country cross wireless 4+,elad fdm-s1,s2,rf space sdr iq,winradio worked okay but could not get the weak signals that i get on my other receivers from icom,palstar,ten tec.

Regards Lino.

Posts: 1353

« Reply #7 on: December 27, 2016, 02:31:16 PM »

Modern rig, or vintage?

While it isn't general coverage and doesn't have a lot of bells and whistles, I find my Yaesu FR-101 to be pretty quiet until you hook an antenna to it. That radio gets used a lot for SWBC and ute monitoring in addition to ham band work. With the right speaker hooked to the rig it's easy to listen to - all day long.

A couple more favorites from the era are Kenwood's R-820 and the Drake R7. These have interference-fighting options built in, as opposed to the Yaesu...which is run with a DSP-599.

The R-820 wasn't general coverage as delivered from Kenwood but it's possible to modify the set so its SW Converter can cover 2MHz swaths near the original 49/31/25/16M allocations. You can then add another band of your choice to its "Aux" bandswitch position.

The FR-101 merely requires plugging crystals into the holder to get additional coverage but darn if they aren't expensive these days!  Shocked

Posts: 81

« Reply #8 on: December 28, 2016, 11:08:41 AM »

Yes, the noise floor of your location is much higher than probably even a cheap all band radio, so reducing the noise floor of your RX is not going to help.

I agree.

Several years ago, I bought a K3 for the "awesome receiver," but it turned out to be too sensitive for HF work in the city.  When the S-meter is moving on the background noise, more sensitivity will only make things worse.  I added a step attenuator to the K3 so that I could optimize the signal level coming into the receiver, but then I just sold it and went with a less fancy radio, because it worked just as well when properly adjusted.

If you absolutely cannot use an outdoor antenna, look at one of the specialized receive antennas.  Instead of a magloop, a small, untuned vertical loop might help you if you have one specific strong noise source, because you could put that source in the null of the loop.  For SWL, I would recommend an electrically small antenna, but not a tuned one (i.e., not a magloop).  Resonating the loop for reception can just make the nearby noise harder to work around.

For SWL, use a step attenuator.  The inexpensive MFJ model will do just fine.  Click in attenuation until the S-meter just barely moves on background noise.  You will be surprised how much that one change will make the noise more tolerable.  It will also make it much easier to point your loop null at the worst remaining source.

Posts: 432

« Reply #9 on: December 30, 2016, 04:11:15 PM »

I think there is quite a confusion when hams speak about the noise floor in a receiver. I think that if you hear a high noise floor is simply that the radio may be very sensitive and this may be counterintuitive but is due to the low noise floor of the receiver. Suppose you have "receiver one" with a minimum discernible signal at -127dbm and with the antenna connected you hear an S3 signal (which is equal to -109dmb). Suppose you also have another receiver, "receiver two" which is less sensitive and has a minimum discernible signal at -109dbm. In this receiver you will not even able to hear the noise with the antenna connected just because the noise floor of the receiver is higher. Paradoxically the quieter the receiver may seem, the noisier may be. This is especially true in the HF. In UHF this may be not as the noise picked by the antenna may be very low.

Having said this, the AOR 7030 was considered a very good receiver. A good receiver such that can be used with wideband or active antennas without problems of overloading. However if the magnetic loop is tunable, this may be very selective and in this case even a portable such as a Tecsun PL660 could give more or less the same results.
« Last Edit: December 30, 2016, 04:20:30 PM by KD7RDZI2 » Logged

Posts: 554

« Reply #10 on: December 31, 2016, 04:21:37 AM »

 I agree. There have been some good suggestions about trying to null the external noise with a directional, untuned antenna.
 A different receiver may not be a satisfactory solution unless it has more provisions than you currently have to limit or filter specific noise types.
 This may come as a compromise, like reduced fidelity/bandwidth, etc. The noise may be sitting right on top of what you are trying to listen to.
 A DSP receiver may be able to take out the noise without disturbing the desired signal too much.
 Most household/apartment RF noises are from switching power supplies. If it is in a neighboring apartment, you might try working with them to identify the culprit and offer a linear power supply replacement to improve your local s/n.
 The noisemaker is likely within 10m of you.
 I don't know your living situation. Do you speak with your neighbor? Who knows, you may share common interests and improve a friendship. Knowing your neighbors on a first name basis has benefits, like improved security, communication and respect, etc for everyone.
 My neighbor collects 78 records and has a Philco similar to one I have. (I have the tabletop version of his console).
 I have gone on drives in the country to escape the city AM noises and it can be just as bad if you are driving next to telephone poles with broadband/DSL cable. The antenna on the car has been the subject of parking lot conversations.
 Experimenting with antennas helped me learn a lot about what works best. Some are homemade. Learning about diversity and propagation characteristics have helped me build antennas that satisfy my needs.

Posts: 5723

« Reply #11 on: January 01, 2017, 08:18:35 AM »

Any time you connect the antenna to a receiver and the noise increases on the recovered audio the receive has a lower noise floor than you can use. As many have said you need a better antenna farther away from the noise sources.

Computers, TV, chargers, digital controllers, anything with digital readout will created noise on the HF spectrum. I might add LED light bulbs are very noisy. Add to that all the other sources from you neighbors.

Your only long term solution is to move to where you have some space around you.

Posts: 907

« Reply #12 on: January 01, 2017, 12:29:09 PM »

K6AER. Mike, I'm not a 'rocket scientist', but I've met a lot of guys that don't understand the 'connect the antenna and look for noise' test.
I once talked to a guy on 6M that had 2 (!!) external preamps in line and the one in the radio. It was a newer radio and he couldn't understand why his resting s-meter reading was 25 over S9......

I see a lot of YouTube videos where the person has a modern radio with preamps engaged and the resting s-meter is S9+.
I'm fortunate that I have a quiet location and the ONLY time I use a preamp, is on 6M and only then when local noise is behaving.
I also don't understand (or believe) the ole', "radio A can clearly hear signals that radio B doesn't even know are there". One of those radios is busted.
SMH.....ha ha
Happy and safe New Year


If you're not the lead sled dog, the view never changes......

Posts: 3030

« Reply #13 on: January 01, 2017, 07:57:36 PM »

"I also don't understand (or believe) the ole', "radio A can clearly hear signals that radio B doesn't even know are there". One of those radios is busted.
SMH.....ha ha"
Yessir, and I  wonder by what mechanism all 1950s Collins military receivers are said to hear more on the AM BCB than modern radios?

Why do so many people believe this crap???  

Posts: 3030

« Reply #14 on: January 01, 2017, 08:12:23 PM »

I think it's fair to say that among better radio brands, useful AM BCB radio sensitivity pretty much maxed out during the Hoover administration.
« Last Edit: January 01, 2017, 08:17:09 PM by K0OD » Logged
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