IC-7300 Receiver Front End Overload

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I was reading a review last evening on Eham and took note regarding a post regarding the IC-7300 Front End Receiver Overload that the user experienced. And was even more surprised to see Icom's answer to the problem at hand.

I am not sure what type of filtering that the  7300 has, but it was interesting to read that his K3 as well as Flexradio did not have this problem. I just wonder how many people are looking at purchasing a 7300 for a possible SO2R scenario? It should be interesting to see how many other comments come out regarding the 7300 with this issue.
Mark Griffin, KB3Z
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Mark Griffin

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Posted 3 years ago

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Barry N1EU

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Indications are that the IC7300 is significantly more susceptible to ADC overload than the Flex 6K and ANAN.  
(Edited)
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Dave Glas

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Why should we read and expect unbiased Icom reviews on this web site? (FWIW: My IC-7300 was excellent; now my IC-7610 is even better!! As always, YMMV.) 73, Dave (WØOXB)
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Bill -VA3WTB

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Well, at that price point. No surprise...
People say all Flexes are too expensive, there are reasons for that cost.
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Walt - KZ1F

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This could actually be a very interesting technical, non cheerleading, non pejorative, discussion. The question I've been asking and never gotten a technical answer on is, given the 6500/6700 and K3S are virtually in a dead heat for top technical honors, I conclude the proximal differentiator is not technology used. Where the price points are also virtually identical it seems to me that leaves margin as the proximal differentiator.

My latest non-SDR is a 30+ yr old Kenwood ts-530sp. It saw several field days in close proximity to multiple other radios. Even though it was 30 or so years ago I do not recall any overloaded front ends or being unable to participate in FD because golly gee, one can't do field day without SDR, which hadn't been invented yet.

Where SDR is so prevalent in cell phones, how is it two people standing next to each other can be on their cell phones at the same time? Yes, I understand they are on different frequencies, so are two people at FD.
(Edited)
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James Whiteway

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Could be miliwatts vs watts. Plus digital signal system compared to the old, analog cell system , improved cell service. It's been years since I could hear other cell calls at times and they could not hear my conversation. Or be talking to someone and all at once be talking to a total stranger!
Much more reliable now. Just improved technology.
James
WD5GWY
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k3Tim

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For CDMA (Code Division Multiple Access) cell phones use spread spectrum and a code (key) for the SS. The code is assigned by the base station via a separate channel. SS is wide band with the RF energy spread out over MHz. The code (key) is orthogonal to others on the channel, so the receiver can decode each individual mobile. An analogy is the "Cocktail Party" effect with a room full of people talking. One can pick out a particular individual conversation given the differences in speech. A problem would occur if someone next to you was shouting and drowned out others. To prevent this the base sends each mobile a "power up / Power down" command many times a second (800 if memory serves). This keeps all mobiles signal strength at the receiver equal. In the field mobiles beside each other do not see interference due to the wideband signal and the processing involved. This also makes the mobile immune to a signal carrier interference. You can tune up all day long on a CDMA channel and not effect it.  Base station handoffs get a bit complicated but that's a whole other topic. There is a master clock at 19.20Mhz that is important to making this all work. It is a TCXO device. 

Hope that helps

k3Tim
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James Whiteway

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Very interesting! Thanks for the explaination.
Learn something new every day.
James
WD5GWY
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AA0KM

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I remember one field day a person  throwing his head phones down because of proximity too close to same frequency.
They had to seperate farther on the 20 meter band as not to interfere with each other.
Antenna spacing in the field I think has alot to do with it.
Good planned field day on antennas helps. ( not wires crossed lol)
I know Flexradio on field day we experimented with TX/RX and had another radio on the same band and the flex would wipe his RX frontend out but not the other way around. The flexradio rx from the other station would show up in the panadapter like any other signal and dial it in and listen.

There is a youtube video about the 7300 overload issue.

73 Jeff

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EA4GLI - 8P9EH - Salvador

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Walt - KZ1F

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Where was the other station and was that scenario manufactured? In the DK6HF vid what displayed on his spectrum looked eerily like what people here have shown and asked "what is this" on. Does that only happen when a physically adjacent station puts 2500 watts into a frequency 1 Khz away? I am not trying to defend the 7300.
James, that wasn't really my point. My point was this could, looking doubtful now, be a thread to, in an unthreatened, non pejorative way, discuss why two radios at roughly the same price point with two different technologies exhibit very similar performance characteristics. This in comparison to two radios, very similar technologies and two completely disparate price points exhibit vastly different performance characteristics. I mentioned cell phones only because they are dirt cheap, SDR, and don't seem to suffer overload. If the answer is, there are a whole lot of components in a non-SDR radio that need real estate and have a cost associated with then in every unit sold, verses whoever did the programming did it once, not once for every unit sold. That being the case, I would expect, based on cost of manufacturing, there would be a huge cost differential that accrues to the SDR manufacturer, esp in the case of US cost of living vs Asian cost of living. From hearing that You Tube video, thanks Sal, I can say with certainty, my 530SP never experienced that and definitely was not an SDR. It's an honest question as my degree was in software engineering, not rf engineering.
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EA4GLI - 8P9EH - Salvador

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I posted the video to save you guys doing the search like I did. I neither endorse the contents neither can I disprove them. 
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Bob - W7KWS -

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It's unlikely cell phones are Direct Conversion like a Flex or a 7300. An ADC operating at 700 to 2100 mHz would be a bit too expensive for any cell phone regardless of its price ($4.99 to $800). Therefore, short of information I've missed, I'm pretty sure that cell phones are fully integrated Superhets followed by DSP. There is plenty of room for limiting large signals before arriving at any ADC.

The overload situation being discussed here results from very strong signals being coupled from an antenna, directly to the ADC in a 7300 or a Flex 6xxx, with either broad filtering or no processing between the two.

Flex 6xxx radios use a 16-bit ADC & the 7300 a 14-bit ADC. That makes the Flex 12-dBv more tolerant to overload Vs. the 7300. My Perseus is 14-bit & is held in high regard by users & by Rob Sherwood but the Flex is better than both the 7300 & Perseus.

Steve Hicks has written & talked extensively on SDR overload. Search these forums & youtube for these discussions & papers.

The CDMA description above is on target but GSM differs still. Both CDMA & GSM are being depreciated in favor of LTE. All three have base station power control of the mobile as described and the uplink & downlink frequency seperation is measured in multi-MHz.

All of this makes cell phones a poor candidate for comparison to HF SDRs.
(Edited)
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Mike, W8BE

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Stubs and band pass filters are your friend on field day.   We use them and stations are about 10' apart with antennas about 50' apart.   Only the 6m station had issues with interference from 40m station.   That was due to us not having a 6m stub on the 40m station.  Other than that 80, 40, 20, and 15 all played well together.
(Edited)
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Ernest - W4EG

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Is this the new Icom IC-7300 forum?
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EA4GLI - 8P9EH - Salvador

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I find this forum a great source of very valuable information regardless of it being related to Flex gear or other subjects. The users of this forum are very knowledgeable and, for the most part, we keep most conversations civil. Moderators hardly ever need to intervene.

I personally do not mind the wealth of subjects.

The IC-7300 intrigues a large number of futurable users of "SDR" or persons looking for a more "affordable" all in one package. I do hope that we can have a technical discussion about it here, the same way I don't mind threads about amps, tuners, antennas, etc. 

If this radio offers close-to-Flex performance for $1500 I want to know.
If it doesn't, because it is $1500 and you can't expect cheap and good all in the same device, I want to know as well.

I second Walt's quantifiers: "[...]a very interesting technical, non cheerleading, non pejorative, discussion".
(Edited)
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Chris DL5NAM

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... have you read the title of the thread?
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Ernest - W4EG

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My point!

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K6OZY, Elmer

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On my IC-7300, I see OVF often on 40M and especially on 80M.  For the money, I still enjoy the radio, but it's no Flex.
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km9r.mike

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That is interesting. I would image you see the same on 160. Does the attenuation help ?
(Edited)
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Bill Roberts

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Just curious, does the problem go away when you turn on IP+ or manually reduce the RF gain control?  Does the radio remain usable (can you still hear the desired signal) when RF gain is reduced.  I would like to use a 7300 for field day but doing so is not the primary intended use.  I just want an SDR lite to take portable in fairly rural Florida.
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Lee, Elmer

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I think the 7300 has a few controls where you can try to tune out overload, but the issue is a relatively weak part that was chosen for the ADC.  Tuning overl oad out may also mean tuning other desireable things out as well. If you are alone at FD it will likely work.  If there are 3 other transmitters within 100ft there may be trouble, and it may depend on the band.  All you can do is try, and it will be a very worthy experiment trying to figure this out in a systematic way. By systematic I mean: if I turn on the preamp the front end crunched, but if I turned it off 10M was dead.  If I hooked up to a beam the receiver crunched but a dipole worked OK etc.  When the 6300 came out some guys set up an all Flex field day and everything worked great and they made a video about it so a video demonstrating success or problems would be useful also.
.
73  W9OY
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Ken - NM9P, Elmer

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Have you ever tried to use your 2 meter hit at Dayton hamvention? Intermodal city! If only my ht front end was as strong as the 6500. I could actually find a clear frequency and talk to my friends!

I used an IC-745 in a multi transmitter field day site and it suffered a bit, depending upon the band.

My TS-850 was a lot better, but limited by the phase noise of the other transmitters, and some overload if I didn't turn off preamps, and sometimes add some attenuation.

I won't be at field day this year. But it would be interesting to try the 6500 some year. But I am hesitant to let it out of my sight! It is one thing to have an old rig worth $800 messed up. It is another thing to risk almost $5000 in a tent at field day.
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Bill Roberts

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I used an IC 7000 in a camping situation where an FT-857 was transmitting 10 feet away.  No issue.  The '857 weakly heard my '7000.  Probably irrelevant as the 7300 is clearly a different radio.
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Cal Spreitzer

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I've noticed that particular EHAM review regarding overload has oddly been removed.  I just went back to read it again and it's no longer listed???? 
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Walt - KZ1F

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I'm guessing that's not something an ICOM fanboy could do, so that adds credibility to the YouTube video being manufactured. Interesting! It goes to eHam technical credibility doesn't it, one side or the other, right?
(Edited)
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Lee, Elmer

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Actually overloading in a SDR is very undesirable.  The radio works great until the last bit is violated then it sounds like listening to 40M CW during sweepstakes on a Hallicrafters S38 hooked to a double extended zepp at 70ft.   

I suspect the radio will have its limitations, but it does come in one spot ahead of the TT Orion on Sherwood's list.   I think this radio given its component lineup and architecture is already pretty much at the pinnacle of its design performance and doesn't have much headroom for improvement.

73  W9OY
(Edited)
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EA4GLI - 8P9EH - Salvador

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I think the Sherwood list position needs to be explain... it seems it obtains a remarkable Dynamic Range Narrow Spaced number (94) when enabling IP+, without that enabled the number is a more average 81 par with IC-703+, Atlas 350 and slightly better than the IC-7800 (80). Sherwood notes: "With IP+ OFF, intermodulation degrades gracefully. Recommend only using IP+ when absolutely necessary due to noise floor degradation."

My understanding of this is that with IP+ Noise Floor raises to -122 (Sherwood measured number) and sensitivity deteriorates. It is almost like me disconnecting the antenna to measure how well my radio block adjacent signals... and it does, the problem is that I also lose everything I was listening to when I do that... which seems to be the case with IP+.
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Lee, Elmer

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IP+ in the 7300 is obtained by invoking the dithering function of the ADC.  It's a technique that is like adding a little bit (pun intended) extra to the bit count which improves dynamics within the chip but it isn't super robust.  

73  W9OY
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Mark Griffin

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Cal,
He has written another review. Once you read his updated review you will understand why he wrote it again!
Mark Griffin, KB3Z
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Paul Christensen, W9AC, Elmer

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'Sherwood notes: "With IP+ OFF, intermodulation degrades gracefully. Recommend only using IP+ when absolutely necessary due to noise floor degradation."'

That's an important point.  The 7300 could (and perhaps should) be listed twice even though dual figures are shown in the 2 kHz DR column.  Although it would be painful to see on a chart, the 7300 is probably more accurately shown in between the TS-830, Atlas 350 and IC-703+.  Why?  Because the IC-7300's normal operation is with IP+ deactivated and that causes a severe hit in its placement in the 2 kHz DR column. 

Although the cause for the change in DR is vastly different in the IC-7300 with IP+ active, it's really no different than ranking a traditional superhet by activating its front end attenuator.  Again, the root cause is different with IP+ since dithering is added rather than hard attenuation, but both examples lead to very deceiving results when ranked on a chart.

Of course, it's Rob Sherwood's prerogative as to how he ranks receiver performance, but when the IC-7300's normal operation is with IP+ deactivated, it seems to me the more appropriate narrow-space DR ranking is next to the Kenwood TS-830. 

Paul, W9AC

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Tim - W4TME, Customer Experience Manager

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Are you asking how to repair an Icom IC-7300?
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W7NGA

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I thought this was a full-service forum!
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Ria - N2RJ, Elmer

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You should call or email icom. They can direct you to an appropriate service center in your country.
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Tim - W4TME, Customer Experience Manager

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Kari has been provided the correct information regarding how to get the Icom repaired.  There is no need for snarky replies.  Hopefully with kindness and respect we show, it will be an opportunity to foster a new FlexRadio customer relationship.
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Mike Lukasik

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I agree with you Tim as we should be more helpful to our fellow Hams. 

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