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Author Topic: IC-7000 cant hear MW broadcast but cheap transistor can?  (Read 13613 times)
CHRISDX
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« Reply #30 on: October 14, 2012, 10:08:08 AM »

Allison there is a coil of coax near the junction block at the start of the twinlead.  But I do now get MW now that I bought a tuner with a bypass switch.  This thread has answered a lot of questions and I am learning a lot.

I would like to mod the radio if possible to defeat the MW attenuator as a next step. There is really no good reason not to since MW cant make it through my tuner when it is switched in.

Anybody care to look at the service doc above and point out any clue as to the nature and location of te attenuator and especially if there is a relay associated that can be jumped or disconnected?
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G8JNJ
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« Reply #31 on: October 14, 2012, 12:14:24 PM »

Hi Chris,

Follow Tom's suggestion - don't modify the radio - it has more than enough sensitivity for MF frequencies even with the attenuator in circuit  - you need to sort out a proper antenna.

The 20dB attenuator is there for a reason, it's to stop the RX being overloaded by nearby / strong BC stations. You will not be able to hear the weaker signals if you remove this. Because spurious / intermod signals will be generated inside the RX.

I can hear amateur stations on 136KHz and 500KHz using my IC7000 and G5RV sized antenna strapped as a Tee and fed against ground. So it works perfectly OK on the MF BC band.

If you are serious about BC band DXing. Build a loop antenna for the frequencies you are interested in. This will improve the RX Signal to Noise ratio and allow you to discriminate between geographically separated stations operating on the same frequency.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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CHRISDX
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« Reply #32 on: October 14, 2012, 01:53:58 PM »

Hi Martin I totally read you on your opinion of the way forward. Actually, the attenuator is my tuner since MW does not make it through. I would like the option to explore different antennas such as various loop options, vertical wire and others and would like full sensitive on the radio. I dont want to be forced to have a limited signal when I can do that outside the radio such as automatically occurs with my tuner, and I could also use a high pass.

Hopefully you and others understand my position. If my radio can be 10x more sensitive internally, I would like that choice for myself. I would not try to dictate what others should do in configuring their shack as these are very near and dear choices we all love to make.

If my 7000 can be made 10x more sensitive internally below 1.8 I would really like to see if any of the very knowledgeable Elmers around here would know just where to make that mod. If anyone here knows how to bypass this artificial limitation inside my 7000 would you please share any info you have, as always thank you!
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AC5UP
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« Reply #33 on: October 14, 2012, 02:13:36 PM »

Count this as one more vote for DO NOT MODIFY THE RADIO !  And, I agree with G8JNJ regarding an RX loop.

There's a reason why so many broadband general coverage receivers employ a high pass filter to attenuate AM BCB stations or use a separate BCB antenna jack... The images of a strong station can raise hell many octaves up the dial. With a decent antenna there is more than enough sensitivity at the low end and since you have a switch, why not build a receiving loop for AM DX'ing? Follow the instructions here... http://members.shaw.ca/ve7sl/loop.html

Except... Build a square loop, 3 or 4 feet on a side, with six turns for the primary coil. One turn for the nested pickup coil that's at least two inches inside the main loop. You want loose coupling. The beauty of a loop like this is a reduced noise level and directivity. With the G5RV you can't null noise or stronger signals. Do some research on the topic you'll find shielded and resonant loops are popular with low band DX'ers because they work. AM DX'ing is not limited by signal strength, it's limited by QRM and the noise floor. A loop addresses both concerns.

Look through the links at the bottom of the page to learn more.

And...... One more Thot.......  DO NOT MODIFY THE RADIO !
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CHRISDX
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« Reply #34 on: October 14, 2012, 03:19:56 PM »

I think we're talking past each other here. I know that it will be fun and productive tpo work with loop antenna options. But the sensitivity still could be better. Of course I can filter OUT the strong BCB RF before it gets to the radio. I still want to find the way to mod the attentuator out of my radio, even though i do hear the concerns - but your concerns should be nulled out by the tuner which BLOCKS BCB totally, or any high pass filter of my choice in the unlikely event my tuner makes a water landing...   Roll Eyes
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G8JNJ
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« Reply #35 on: October 15, 2012, 08:42:45 AM »

Hi Chris,

Please do not modify the radio to make up for an external problem.

I don't know how much experience you have working on modern surface mount PCB's. I have a reasonable amount, but I wouldn't risk it with my 7000.

Fix the source of the problem instead of applying a workaround.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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CHRISDX
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« Reply #36 on: October 15, 2012, 08:54:33 AM »

The source of the problem is that a signal below the 20uv sensitivity wont be processed by the radio. I can get more signals above 20uv by improving the antenna, but there will still be weak signals that COULD be heard without the attenuation. So THAT problem is inside the radio. Of COURSE I would not find a way to switch it off on my own I am not a digital radio tech. But I am hopoing to find someone here who can do just that.

Put it this way, I want to move the <1.8 attenuation to OUTSIDE the radio where *I* can control it, not be forced to listen only to stronger stations because it cant presently be switched off.

Hopefully I didnt stumble upon a IC7000 purity religious cult here  lol it is just a radio and I am a hobbyist looking to get a choice in MW attenuation, and there is nothing wrong with wanting to do the attenuation optionally rather than mandatory.
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VE3FMC
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« Reply #37 on: October 15, 2012, 11:27:52 AM »

I must be in the AM  hotspot because as I said in my earlier post I can receive lots of AM stations on my Icom 7000 with the 80 meter dipole. In the middle of the afternoon I can copy stations through out the AM broadcast band. 1010 out of Toronto is 10/9 right now. 120 miles from me, I think that is a pretty decent signal.

I know one thing, I would not mod a HF rig that set me back $1500 when it was new so I could listen to broadcast stations. A cheap AM radio would work fine for me for the amount of AM stations I want to listen too. But hey it is your radio not mine, mod away if you think it will help you.

IMO you need a better antenna not only for AM broadcast reception.
« Last Edit: October 15, 2012, 11:32:23 AM by VE3FMC » Logged
CHRISDX
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Posts: 244




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« Reply #38 on: October 15, 2012, 02:03:33 PM »

Rick I still need to test the limits of my BCB reception anyway now that I have learned the tuner was in the way (and replaced it with a similar tuner that has a bypass switch).  I also need to add a loop as well. In order to work with a loop, it will probably have to be in here with me in the living room, although I could put a loop of about 5' diameter in the attic above and have a large knob in the ceiling to rotate it, or better yet coming down the wall with a wooden lever, the top (in attic) would have a bellcrank with a push pull rod about 10' to the attic center where the loop can be mounted in a bearing. That would get me close to 180 degrees of rotation which would cover all directions.

There are wires around my attic, I wonder if that will affect the loop's performance or properties?

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VE3FMC
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« Reply #39 on: October 16, 2012, 11:51:14 AM »

Rick I still need to test the limits of my BCB reception anyway now that I have learned the tuner was in the way (and replaced it with a similar tuner that has a bypass switch).  I also need to add a loop as well. In order to work with a loop, it will probably have to be in here with me in the living room, although I could put a loop of about 5' diameter in the attic above and have a large knob in the ceiling to rotate it, or better yet coming down the wall with a wooden lever, the top (in attic) would have a bellcrank with a push pull rod about 10' to the attic center where the loop can be mounted in a bearing. That would get me close to 180 degrees of rotation which would cover all directions.

There are wires around my attic, I wonder if that will affect the loop's performance or properties?



I would try different antennas before I did any mods on the radio.

How far are the stations located from you and what is the power of those stations? At night I have copied AM stations from ranges of 400-600 miles from here.

Remember daytime reception is not as good as evening reception.
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AA4PB
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« Reply #40 on: October 16, 2012, 12:40:28 PM »

Go back and re-read W8JI's comments. If you mod the radio to get 10x more sensitivity you will pick up more noise along with the additional signal and the signal to noise ratio will stay the same. Receiving is all about signal to noise ratios. That's why low frequency receivers don't require a lot of sensitivity. If you can hear the noise level increase when you connect the antenna then more sensitivity will do you no good.
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KG6YV
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« Reply #41 on: October 16, 2012, 02:27:52 PM »

 large toggle switch lik the 20 Amp switches sold in automotive stores are OK for 100-200 watts.
above that power level voltage may just melt the switch. 

Greg
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N4NYY
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Posts: 4758




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« Reply #42 on: October 16, 2012, 03:21:22 PM »

Chris,

I have a Grundig S350DL that I use for AMBC DX, mostly for baseball games. The radio was under $100. I modded it with Kiwa aftermarket filters. The radio works great. Now, I think it was replaced with the S450DL, which is PLL based.

FWIW, I have restored a couple old 1950's tube radios that picked up baseball games from Detroit and Toronto, as well as hockey games in the Tennessee and NC area.

Ask AC5UP. You can get great old transistor rigs that have long distance AMBC reception, on ebay for like $40.

I am with the "Do not mod the Icom" group.
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AC5UP
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« Reply #43 on: October 16, 2012, 04:31:21 PM »

...and one of the better choices for the avid AM BCB DX'er is an older car radio. Personally I prefer a 70's or 80's Delco with analogue tuning despite the vagueness of the dial. Not only were they permeability tuned like an R-390  Shocked  but it can be useful to tune slightly off one side of a station when there's a stronger signal on the other side. One of the better efforts from Delco was their AM Stereo model from the 80's. Rare, but they had an IF bandpass that rivaled a good communications receiver. I'm also partial to German car radios of the Blaupunkt and Becker persuasion, plus I've had Honda radios that were definitely overachievers.

But, for the person looking for minimum hassle plug & play, it's hard to beat a 60's Zenith Royale, GE lunchbox or GE SuperRadio II. Do not assume the SuperRadio III is better. It isn't. The advantage to the larger portables is the directivity of an oversized ferrite bar antenna, larger speaker, and the ability to run from battery... Which is always a zero hum and zero noise power source.

For those of you who haven't done so in a while, go out to the car after dark and fire up the AM side of the radio for a comparison to other radios you may use for AM BCB. More often than not they'll offer better reception and much better sound quality than the typical general coverage receiver........ Plus they do the FM Stereo thing when you need a break from talk radio.

Note To N4NYY:  If you score a really good car radio you might pick up signals from an alternate universe where the Yankees are winning their playoff....   Grin
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N4NYY
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« Reply #44 on: October 16, 2012, 04:51:55 PM »

Quote
But, for the person looking for minimum hassle plug & play, it's hard to beat a 60's Zenith Royale, GE lunchbox or GE SuperRadio II. Do not assume the SuperRadio III is better. It isn't. The advantage to the larger portables is the directivity of an oversized ferrite bar antenna, larger speaker, and the ability to run from battery... Which is always a zero hum and zero noise power source.

I had the Superadio III. The Grundig blows it away. The SRIII drifted like an unanchored boat.
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