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HF/MW/LW Equipment - For general and technical discussion of all receivers which cover the HF bands. For HF tranceiver discussion please use the Amateur Radio Equipment forum above.

View Poll Results: Out of these three, which one would you choose?
Tecsun PL-660 3 37.50%
Tecsun PL-880 4 50.00%
Sangean ATS-909X 1 12.50%
Voters: 8. You may not vote on this poll

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  #21 (permalink)  
Old 07-10-2018, 6:23 PM
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I've done that - spent many a year putting fingernail grooves into the front faceplate paint of R-390's in another life manually tweaking as a compromise.

I think getting agc right is a significant challenge for radios designed from the start as broadcast receivers looking for steady-state or even fading signals.

It's a lot of retro-fun to ride the rf-gain, but significant issues arise like when trying to use the Grundig 750 with it's bad agc:

Airband - should be fast-attack and fast decay. Riding the rf-gain manually here is ridiculous. Lots of missed readbacks from the tower, and blown out syllables. Not really usable unless one gets this right.

Cw - same as airband: fast-attack, fast decay.
SSB : fast attack - generally slow decay.

Maybe getting that into a portable would just push the price point up too far to be profitable. Just hammering down the rf gain is in my opinion is an over the top indication that the rigs just don't know how to handle it.

Your noise level - I'll bet you've tried many different antennas. Have you tried the "loop on ground"? While not in itself some sort of magical cure, it may at least let you run with an agc again...
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  #22 (permalink)  
Old 07-10-2018, 8:44 PM
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Quote:
Originally Posted by hertzian View Post
Airband - should be fast-attack and fast decay. Riding the rf-gain manually here is ridiculous. Lots of missed readbacks from the tower, and blown out syllables. Not really usable unless one gets this right.
Well, airband, if you mean VHF, has never been a problem for me, as I live only 2 miles away from our local airport. There's lots of activity from pilot training and water bombers here during our wildfire season (the water bombers have a base at our airport). Not only that, but the tower uses only one frequency, so I have programmed my scanner with its non-functioning LCD with only that frequency. Scanning is not necessary, so there's no need to display anything.

If you were referring to the MWARA frequencies, they are very difficult to hear at my location, especially the North Atlantic routes, probably due to the mountains to the east of us, but when I do hear them I wouldn't want to decrease the gain, as they are very weak to begin with.

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Originally Posted by hertzian View Post
Cw - same as airband: fast-attack, fast decay.
SSB : fast attack - generally slow decay.
On the R75 I've always set both of them to fast, but the indicators only show AGC or F.AGC, so I'm not sure whether fast and slow applies to both attack and decay or not.

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Originally Posted by hertzian View Post
Your noise level - I'll bet you've tried many different antennas. Have you tried the "loop on ground"? While not in itself some sort of magical cure, it may at least let you run with an agc again...
I have no access to the ground, hertzian, as I live on the third floor of an apartment building. It's not even possible for me to set up an outdoor antenna. The only experimentation I've done is with various lengths of random wire antennas. Currently the best one I've tried is the 23 ft. reel antenna that came with the ATS-909X. I have strung it horizontallly along an outside wall less than a foot from the ceiling (I'm on the top floor), and have added a bit of lead-in via a headphone extension cord. This way I can plug it straight into the radio's antenna jack. I also had to jury rig an adapter so that I could connect it to the R75's coax socket when I want to switch radios. It's a PL-259 connector with a very short piece of coax, at the end of which is an alligator clip on the center conductor. When I want to use the R75 I clip that to the center conductor of my makeshift antenna lead-in. It works quite well, although I actually derive very little benefit from using the R75, since the noise level is even worse that way, and the signals are no stronger than with the portable.

I never seem to have lived anywhere that's an ideal location for radio. Probably the best reception I've ever experienced was on the Canadian prairies, using the R75 with a Sony AN-1 active antenna mounted outside about 10 feet above ground. The flat terrain was a great help, but that was in the 90s, and propagation was superb back then.
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Old 07-11-2018, 10:09 AM
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One more vote for the 660. I love everything about it, except that it goes through eneloops pretty quick.
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Old 07-11-2018, 3:16 PM
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CW should be fast attack and slow delay - otherwise the noise comes up between words - or worse, between letters - but it's a compromise, depending on the senders' speed. Riding the RF gain still works for me, even better if you have a narrow RF or audio filter - the signal just pops out of a quiet background. You'll find most commercial radios have the RF gain on the left hand side specifically for this purpose - pity the poor leftys! Next to the handle so you have something to hang on to when the ship is rolling all over the place!

They called it "Sensitivity" here, but it does the same job....
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  #25 (permalink)  
Old 07-12-2018, 4:04 AM
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Originally Posted by GB46 View Post
It works quite well, although I actually derive very little benefit from using the R75, since the noise level is even worse that way, and the signals are no stronger than with the portable.
Oh man, don't I know how frustrating that is! I hate to see the R75 not being used. I too have lived in crappy locations, and over the years the qrm has gotten worse - so much so that even rotatable loops are not effective because nothing is a point-source anymore.

Seems like the entire neighborhood is running BPL in the homes, with only the amateur bands notched out +/- a few 100 khz each side. (At least that allows me to swl bands close to the ham bands like 41 meters, and do ATC monitoring of SFO radio on 10.057 usb.)

What I've had to do in the past was to run my R75 solely from a large-ish agm 12v battery which I recharged when necessary to totally isolate myself from the housing ac lines. That was the first step.

Then, using a portable shortwave receiver, tune it to ssb (rather than am to make hearing the noise nulls easier) and side-step inch by inch through my whole interior looking for the lowest noise. Even though it doesn't sound like it makes sense, the shortwave portable antenna was walked around in the vertical position. Eventually, I found about a 6-inch wide section where I wasn't in the immediate noise field of some noisemaker. I mean it was NARROW, but I found a spot with the portable receiver. (an Icom 817 qrp rig actually)

That is where I planted a small vertical, like a tabletop version of the "MP-1" super antenna with it's sliding coil.

Even with that, I had to make sure I choked the somewhat small coax run from the table over to it, to make sure that my coax common-mode of the shield wasn't in a noise-field.

THIS is where you could homebrew, or even something like the Apex 303-WA-2, even if indoors next to a window might help. I reviewed it here before. Basically 6 feet or so of vertical radiator, some sort of lossy wideband match, and also some sort of disconnect to make the coax less of a problem with common mode. Ie, radials don't help it either. BUT, the primary concern is to get the s/n floor down by finding a very narrow vertical position, and isolate the coax common-mode with some form of choking they use.

With the R75's double-preamps, it might just be usable in your situation.

Just some thoughts. Maybe you could tune to say 10.057 usb (to be sure you aren't in a bpl field - and frequency not critical but stay within the amateur bands for this test - even if you only do broadcast swl), keep your portable receiver antenna vertical, and side-step inch by inch through the property.

It's a pita for sure. That and running from battery like an 18 - 20ah agm you'd find in an old-school jump-starter. The R75 pulls about 900ma to 1A, so you could get about 10 hours use (about 50% discharge, which you don't really want to exceed before recharging with lead-acid worst case if you want more than a few hundred cycles from it)

Just some thought for those of us who refuse to give up!

Last edited by hertzian; 07-12-2018 at 4:10 AM..
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  #26 (permalink)  
Old 07-12-2018, 4:19 AM
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Majoco - now that's a nice receiver!

Thanks for the correction about the cw agc. Typing too late at night.

The whole agc thing just bugs me on the portables. The Grundig 750, with airband was just a pain to control manually. Differing signals strengths of incoming and outgoing planes, slow agc combined with an audio-derived squelch, rather than rf-derived just made it all too unpleasant.

Obvious solution - reach for a different tool - even the inexpensive Uniden BC75xlt scanner was like gold compared to the Tecsun S2000 aka Grundig 750.

My thought was that if it seemed like just a goof to fiddle with for an hour, and then ignore because it was just too cumbersome to enjoy, remove that feature altogether, and put the money back into the primary function of shortwave..

Stuff like that drives the radio-nerd in me nuts. But then again, I'm not really the major demographic for most marketing departments.
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