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Author Topic: IC-7000 cant hear MW broadcast but cheap transistor can?  (Read 14608 times)
CHRISDX
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Posts: 244




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« Reply #15 on: October 10, 2012, 11:40:03 AM »

If the toggle joins the center of the incoming and outgoing coax within the switch, then when it is open (off) why would it need to handle transmit pwr? Or have any impedance?  It would only be on when receiving bands out of the switch's ability such as MW. 
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AA4PB
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« Reply #16 on: October 10, 2012, 12:53:37 PM »

If the toggle joins the center of the incoming and outgoing coax within the switch, then when it is open (off) why would it need to handle transmit pwr? Or have any impedance?  It would only be on when receiving bands out of the switch's ability such as MW.  

If the switch only joins the center of the incoming and outgoing coax together then the tuner elements are not completely out of the circuit when the switch is closed - there are still elements between the coax center lead and ground. When it is open then there could easily be some high voltage across the switch contacts during transmit on some frequencies. This also leaves the coax shield connected when in the bypass mode. I think you'll find that the antenna performs better on the BC band if the shield is left floating so that the whole antenna performs more like an end-fed long wire as described by G3RZP.


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N4NYY
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« Reply #17 on: October 10, 2012, 01:25:17 PM »

We have a VERY small house and my station is comprised of the IC7000 and pwr supply, tuner, switch next to the recliner. I also am restoring an old Hallicrafters which the modern rig will sit on top of. Point being, space is at a premium here.

This thread helped me figure out something that should have been obvious   Embarrassed   and now it's time to put the new knowlege to use.

How to add a bypass switch to the manual tuner that wont hurt its performance is the logical step. Way better than moving the radio out and unscrewing the coax everytime I want to catch my talk show or weather and traffic report or do some MW DX at night. Also can have a long wire and try a homebrew loop on switch positions 3/4

Any issues or advice for adding a bypass to the tuner? Can I just jump the capacitors etc with a toggle? Should the switch leads be shielded with the shields grounded?


Chris, would it be easier to just run a random longwire, like Bell wire, and just manually make the switch? I am about 120 miles NYC, and have no problem picking up Yankees games on my 950. The thing is that it is not that appealing to do it on a 950. Also, I like to spend time outside to listen to the games. 
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G0GQK
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« Reply #18 on: October 10, 2012, 02:11:31 PM »

Try just pushing a piece of wire about 10 ft long into the centre of the appropriate antenna connection

Mel G0GQK
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CHRISDX
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Posts: 244




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« Reply #19 on: October 10, 2012, 03:25:28 PM »

Thanks guys. But as the OP here I would like to move to the part where I add a bypass switch to my tuner, trust me its the best solution for my compact station.

MFJ makes a small tuner with a bypass button, MFJ-941E but some eham reviews say it isnt thyat great (it arcs internally under load).

My MFJ-971 has been good so I'd rather save the $$$ and just give it the ability to bypass.

So, with that said, can I just add a toggle and some short wire from the center of the input and output S0-239's?

again thanks for the various tips so far
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VE3FMC
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« Reply #20 on: October 10, 2012, 04:25:42 PM »

Just so you all know about the ability of the Icom 7000 to receive commercial broadcast stations.

I can copy the local airport beacon on an 80 meter dipole.

I can also copy broadcast stations from the bottom of the AM broadcast band right up to the top end of the band. Stations range in the distance from local stations and New York City, Chicago etc. I am located in south west Ontario.

Currently copying a station out of Toronto, which is about 120 miles from me and that signal is peaking 10/9 without the preamp. With the preamp on I can still copy that station on a 10 meter ground plane that is 25 feet off the ground. On a 2 element tri band at 32 feet I can copy the same station at S 9 off the back of the beam.

So I would say that anyone who says Icom's have poor receive below 80 meters are wrong. I have owned 3 Icom's, a IC-720, IC-718 and my current IC-7000 and all have worked fine on receive on the broadcast band.

If the original poster does not want to take the tuner out of line then he might try adjusting it will listening to an AM Broadcast station. When I have my Palstar tuner inline and adjusted to the bottom of the 80 meter band for my dipole I can not copy that station in Toronto. A local station which has it's antenna 15 miles from me is only S 4 with the preamp turned on. By adjusting the inductance on the tuner I can bring the signal up to S 9.

So the tuner is problem. With the tuner by passed that local station is 50/9 with the preamp on, 40/9 with the preamp off.

On the same antenna, the same broadcast station is 20/9 on my FT-950. The preamp does not operate on the AM Broadcast band on the FT-950.

I am pretty sure my Icom 7000 receives on the AM broadcast band quite well.
« Last Edit: October 10, 2012, 04:36:50 PM by VE3FMC » Logged
CHRISDX
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Posts: 244




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« Reply #21 on: October 10, 2012, 04:36:06 PM »

Found (and ordered) my solution./  Switching to this tuner gives me 6m ability too.  I can have the following antennae:

Alpha Delta Ant #1  G5RV
Alpha Delta Ant #2  10M Vertical
Alpha Delta Ant #3  6M
Alpha Delta Ant #4  AM/BCB wire (try various)



http://www.mfjenterprises.com/Product.php?productid=MFJ-945E
The tuner has a bypass switch which should solve the problem and I wont have to unscrew coax to use BCB
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NO2A
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« Reply #22 on: October 10, 2012, 10:36:05 PM »

Hi all,  I have an IC-7000 transceiver with a G5RV and it works well on the ham bands, 80m, 40m, etc but it can only get one or two very strong local AM stations, yet the cheap portable radio can hear them.  Also I have a Kenwood HT TH-F6A which when switched to the internal bar antenna, can hear some AM stations but not as well as the transistor.

Is this an antenna type issue, or is the Icom just deaf down low? I can do better with a crystal set!  lolThe F6 will work much better if you connect an sma to so-239 adapter,then put a few feet of wire into that. Don`t use the built in bar antenna,as it`s deaf. This will work better for hf than broadcast,because the sensitivity for those bands is really bad. Many hf rigs use a front end attenuator on the broadcast bands. You may notice if you go from 160m to am broadcast you`ll hear a click as it engages. If it sounds like you lost 10-20 db gain,that`s what happened.


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CHRISDX
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Posts: 244




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« Reply #23 on: October 13, 2012, 05:26:11 PM »

Got my MFJ-945E today. First try it seems like a good little tuner, and it has the bypoass switch so I get moderate MW performance. The old tuner (with no bypass) was filtering out the MW band.  But I can get 740 Toronto in my car, but not on the Icom with the G5RV (can get many other stations though). Someone mentioned an attenuator that switches in, I'd like to find that but also I will get an old AM car radio and try in in place of the IC-7000 just to rule in or out the antenna, location, etc.
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W9GB
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« Reply #24 on: October 13, 2012, 06:08:36 PM »

Quote from: CHRISDX
I have an Icom IC-7000 transceiver with a G5RV antenna and it works well on the ham bands, 80m, 40m, etc but it can only get one or two very strong local AM stations, yet the cheap portable radio can hear them.  ??
Chris -

Jim, W5JJG actually gave you the correct answer (reason for AM BC attenuation).

One of my Elmers, K9EWK(sk) was a broadcast engineer and installed many AM/FM stations from 1952-1976.  
He routinely had this same complaint with the Japanese mfg. HF transceivers with general coverage receivers, so I learned about this issue long ago (and his solution).
This attenuation design was fairly universal with Icom, Yaesu, and Kenwood, he had the top HF transceivers from each mfg. over a 30 year period.

IF you pull up the Icom IC IC-7000 schematic, you should find a 20 dB attenuator that is automatically switched ahead of the first RF amp when the general coverage receiver tunes below 1.8 MHz (lower edge of 160 meters).  In older radios, you could actually hear the relay energize to "cut-in" the attenuator circuit.
This automatic attenuation MAY be a Menu option on your IC-7000.

His solution on earlier radios was to jumper this or defeat the automatic switch over.  
In recent HF transceivers, this is a jumper at the front-end OR a menu option (user config).

IF he needed attenuation for a local AM station, radios such as the Icom IC-756ProIII
had a front panel push button to ADD the 20 dB attenuation manually.
« Last Edit: October 13, 2012, 06:22:17 PM by W9GB » Logged
CHRISDX
Member

Posts: 244




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« Reply #25 on: October 13, 2012, 10:45:35 PM »

OK I went looking for a schematic (still looking) but the manual lists AM sensitivity up to 1.8MHZ is 13microvolt, and above 1.8MHZ it drops to 2microvolts. So I am certain you are right. I am no electronic tech so I'll look for that menu option. If there is none, I'll certainly need some kind of help getting the attentuator disengaged if possible...




Quote from: CHRISDX
I have an Icom IC-7000 transceiver with a G5RV antenna and it works well on the ham bands, 80m, 40m, etc but it can only get one or two very strong local AM stations, yet the cheap portable radio can hear them.  ??
Chris -

Jim, W5JJG actually gave you the correct answer (reason for AM BC attenuation).

One of my Elmers, K9EWK(sk) was a broadcast engineer and installed many AM/FM stations from 1952-1976.  
He routinely had this same complaint with the Japanese mfg. HF transceivers with general coverage receivers, so I learned about this issue long ago (and his solution).
This attenuation design was fairly universal with Icom, Yaesu, and Kenwood, he had the top HF transceivers from each mfg. over a 30 year period.

IF you pull up the Icom IC IC-7000 schematic, you should find a 20 dB attenuator that is automatically switched ahead of the first RF amp when the general coverage receiver tunes below 1.8 MHz (lower edge of 160 meters).  In older radios, you could actually hear the relay energize to "cut-in" the attenuator circuit.
This automatic attenuation MAY be a Menu option on your IC-7000.

His solution on earlier radios was to jumper this or defeat the automatic switch over.  
In recent HF transceivers, this is a jumper at the front-end OR a menu option (user config).

IF he needed attenuation for a local AM station, radios such as the Icom IC-756ProIII
had a front panel push button to ADD the 20 dB attenuation manually.
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CHRISDX
Member

Posts: 244




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« Reply #26 on: October 13, 2012, 11:19:28 PM »

UPDATE there is no menu option to turn off the MW attenuation on my IC-7000 so I'll be looking for someone who can work on this radio as I'm sure with the 2uv to 13uv sensitivity drop at 1.8MHZ, its there...

I found the service manual here:
http://www.repeater-builder.com/icom/pdfs/icom-ic-7000-sm.pdf

I dont think this language applies to our issue but it says this about below 1.8

The signals below 1.8 MHz are passed through the low-pass
filter (L103, L104, C106, C110, C111) and then applied to
the preamplifier circuit.
The other band signals (1.8–60 MHz) are passed through
the high-pass filter (L105, L109, L110, L116, L117, C108,
C109, C114–C116) to suppress strong signals below
1.8 MHz and then applied to the low-pass and high-pass filter
circuits.
« Last Edit: October 13, 2012, 11:26:21 PM by CHRISDX » Logged
W8JI
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« Reply #27 on: October 14, 2012, 05:06:51 AM »

Chris,

Some late comments:

First about eHam reviews. Don't put so much stock in what they say. They are a combination of emotions and feelings more than something exclusively technically accurate. The more prone something is to operator error the less favorable the review. The worse the general reputation of a company the more accepted a bad review is. If you look you can find things that don't work at all but come from a favorable place that get reviews like "it did not work at all and I put it in the closet, but it is a 4 out of 5".

Back to the topic. Signals and noise are so strong on lower frequencies, like the AM BCB, that 20 uV is far more than enough level. You might worry about 1-2 uV on ten meters in a quiet location, but not on low bands. The exception would be with a terrible antenna.

The single largest issue you will have is impedance mismatch between the receiver and the antenna source. You are cutting up a receiver, or thinking about cutting up a receiver, when some very simple outside changes are all that are necessary.

If you pull the antenna off and hear a large background noise drop between busy channels, you have all the sensitivity or antenna matching you need for that antenna.

If you do not have that happen, you should probably look at simple external ways to improve antenna match to the receiver before worrying about removing the attenuator.

My largest problem around the house with my old BCB radios is noise around the house from all the SMPS and other things making noise now. I have to pick antennas for reduced noise from devices around the house, rather than sensitivity.

73 Tom
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N3QE
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Posts: 2287




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« Reply #28 on: October 14, 2012, 05:19:56 AM »

Any thoughts on adding a bypass switch on my MFJ-971? I dont want to make a design mistake that would degrade the tuner in any way.

The most effective solution will be going to Radio Shack and buying a $10 AM transistor radio. (Assuming they still sell them!)

The IC-7000 is a fine CW/SSB ham rig but its filters and AGC will never be as perfect a match to the AM broadcast band as a $5 or $10 transistor radio. It would seem a shame to hack up fine ham equipment just to get it to be an AM radio.

If you want to do BCB DX'ing, find a slightly more accomodating AM radio (car radio from the 70's, "GE Superradio", better tabletop radios from the past) and supplement with an external receiving loop antenna. Winter is coming and BCB DX'ing can be quite interesting especially with receiving loops to null local stations. I've only ever dabbled in it but when the ham bands are empty and there's an AM signal every 10 kHz, and AM signals are popping up in between from Europe or South America, it is tempting.
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KB1GMX
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« Reply #29 on: October 14, 2012, 06:03:31 AM »

I'll bet there is a balun or other coupling device on the G5RV that blocks MW.

Allison
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