IC-7000 and it's VHF/UHF
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High again all.
I was wondering what your thoughts were about the IC-7000's VHF/UHF mode. I find the receive performance on both bands to be very poor. I have a FT-7800 that just blows the 7000 away. I have also compared it to other vhf/uhf radios and the Icom falls very short on the receive. What is your experience with it? 73 n2gyn John |
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Can you be a little more specific on how the 7K falls short?
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I have an FT-8800 and have compared it to my 7Ks, both on the air and on the bench with an Agilent 8924C analyzer. On the bench, the 7K has better sensitivity than the FT-8800. The 7K has 12 dB SINAD at -125 dBm (Preamp ON), while the FT-8800 is at -121 dBm for both VHF & UHF. The S-meter calibration for the 7K is S9= -84 dBM for VHF and -91 dBm for UHF(preamp ON) versus -91 dBm for both bands on the FT-8800. The 7K is meant to be used with the preamp on. In a strong signal environment the 7K is less susceptible to intermod than the FT-8800, especially if you turn the preamp off on the 7K. The FT-8800 doesn't have an switchable input attenuator or preamp. I work weak signal SSB on 2M and 70cm with the 7K with good results. For public service events I use both radios side by side and in the fringe areas of repeater coverage on long bike courses the 7K has slightly better reception than the FT-8800, but most of the time I can't tell much difference. Steve, W3AHL --- In ic7000@..., "n2gyn" <linyc@...> wrote:
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Hi All and thank you for your replies.
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First a little back: I have been a Ham for over 35years and in that time have owed many many radios. The LONG AND SHORT of it......, I know what I am doing. So..........., I have so knowledge. I am using the same base antenna in all my comparison in FM mode. I have tested with, and without the pre-amp. From what I am hearing here on the forum their must be something wrong with the radio I have. Just an example. A signal on my FT-7800 or my FT-2800 will show and s-10 and be very readable. On the 7000 s-2. And almost unreadable. I have to sit in front of my house with 35 watts for the 7000 to see a 40 over signal. This holds true for both VHF and UHF. So something is not right. John N2GYN P.S. Please......,No green horn questions. ===================================== --- In ic7000@..., "Steve W3AHL" <w3ahl@...> wrote:
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There is almost no common circuitry for VHF & UHF RX on the front end, except a low pass filter. One thing that has always bothered me is the lack of any static bleed resistor or internal spark gap on the VHF/UHF antenna input (the HF input has both). Most dual band antennas have a DC short due to their matching network, so typically this isn't a problem.
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But it's possible that a static discharge or lightning has damaged some of the input components. The first preamp FETs are pretty far down the chain and usually don't fail. The LC filters or steering diodes are more likely. Or it could just be a problem with some of the control signals, but it would be unusual for it to affect both bands. It should be an easy problem to trace with a signal generator and scope or spectrum analyzer. Steve, W3AHL --- In ic7000@..., "n2gyn" <linyc@...> wrote:
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This all makes good sense.
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Thanks Steve. N2GYN John ============================= --- In ic7000@..., "Steve W3AHL" <w3ahl@...> wrote:
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Yes I have found this to be true. However..., It still is very on VHF/UHF. I did find this video very helpful. http://www.youtube.com/watch?v=FlkbPIMEFos It shows you how to increase the gain in the hidden service menu. I tried it, and it worked well. But still not as good receive as my FT-7800. Thanks to All that replied. John N2GYN |
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I'm not sure who you are replying to, since the last post to this thread was in April. ?But the adjustments for RX sensitivity shown in the video are a good example of what NOT to do ...usually. ?Adjusting RX gain based upon what the band's noise floor is can result in severe intermod when strong signals are present. ?Or if you have a high noise level, then would you reduce sensitivity to get rid of the noise? RF designers (and marketing) will push every usable dB of gain they can get out of the RX circuits, balanced by maintaining acceptable performance for other metrics such as blocking dynamic range, 3rd order IMD, etc. ?They don't back off on RX sensitivity performance, since that is the easiest and cheapest part of the design, since everything downstream in the IF's limits how much gain is usable. ?Now if you are in a really quiet location with no strong signals from repeaters, you MAY gain a little, but there are better ways to get more signal to the shack, without messing up the radio. I've seen the results of casual tweaking several times, when local hams would complain about how a local repeater was splattering all across the band and we should do something to fix it. ?I did fix it, by using an analyzer to set up their radio the way it was designed, rather than in "turbo" mode. ?This phenomenon isn't restricted to the IC-7000, unfortunately. All of the 7K's I've tested met their RX sensitivity spec's on HF, VHF and UHF (except for a couple that had the first preamp stage damaged due to lack of lightning suppressors) -- which are practically identical among comparable rigs. ?Look at the ARRL lab tests to see how the 7K compares to an FT-857D, TM-V71A, etc. ?All of them have VHF/UHF FM sensitivity around 0.16 uV or worse and SSB sensitivity around -140 to -142 dBm. ?The only sensible way to get more usable gain on VHF/UHF is with a better antenna/feed line or a pre-amp on the mast if you are really looking for weak-signal SSB stations. Another 7K owner frequently posts recommending changing the Total TX Gain adjustment so you can get a full 100 watts out at 10 VDC supply voltage (with no IMD or spurious emissions). ?I haven't been able to recreate his claims, because the overcurrent protection keeps cutting back the power to 75 watts or lower. ?If I override the APC setting, then the 3KHz wide signal splatters +/- 10-15KHz during modulation peaks. Resist the temptation to twiddle the knobs in service mode, unless you really understand the bigger picture. Steve, W3AHL |
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This is all good information Steve. However...., the fact remains. The VHF/UHF on the IC-7000 is NOT as good as most 2m/440 mobile rigs. This fact eats at my very core! That's why I brought it up again from the last post in April. Using the SAME antenna for testing their is a noticeable difference. You are NOT addressing a newbe Ham here. I may not possess the technical knowledge you have, but I know what I know. The IC-7000 is disappointing on 2m/440. Bottomline!! Have a very nice Holiday. 73 John |
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I just don't see the problem here. ?I have an FT-8800 and access to several TM-V71A's to compare to my two 7K's. ?There are several repeaters that are marginal coverage for my area. ?Doing an A/B test among the 4 rigs has the two 7K's neck-in-neck with the TM-V71A, with the FT-8800 clearly in second place. ?The TM-V71A has slightly better quieting on some repeaters perhaps, but the signals are so weak it's hard to judge reliably by ear. I don't doubt what you say. ? Can you give any more details on what and how you are comparing? ? If you hear a dramatic difference, I would suggest you find someone with an analyzer and check out the sensitivity at 12 dB SINAD. ? Maybe there's a problem with your radio. Steve, W3AHL |
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Steve..., You can check out the links below and see how it is a known issue that the radio has poor sensitivity on 2m/440 http://www.eham.net/ehamforum/smf/index.php?topic=63406.0;wap2 http://forums.qrz.com/archive/index.php/t-312382.html You can also do a search on Google about it. It's not a dramatic difference from other radio's, but it is big enough to notice. Try to find a very weak signal on simplex, then switch to another 2m/440 rig. You will then see the big difference. It's the difference between hearing and understanding a very weak station, to hearing nothing on the IC-7000. Compare the radio in real life terms. One will not see the big difference on local repeaters. N2GYN John |
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I still stand by my earlier assessment, based upon personal experience and accurate test data on the air and on the bench. ?Given previous claims that the 7K RX is weak on VHF/UHF, these weren't?casual tests and are repeatable over weeks of time. The "local repeaters" are close to 100 miles away and the signals out of the coax are -120 to -123 dBm (0.22 - 0.15 uv), which is right at the specified 12 dB SINAD sensitivity of the 7K and TM- V71A. ?None of the radios are full quieting, but copyable. ?I could repeat the test using simplex, but not sure how a simplex signal at -123 dB differs from a repeater signal at -123 dB. I work weak-signal SSB occasionally on 2M when the band is open. ?Signals that are below the noise floor of my analyzer (-132 dBm) are clear when band conditions are stable. ?For comparison, S1 is -105 dBm on 2M with the preamp ON. ?I live in a rural area and noise levels are low (if I power down a few things in the shop). I suspect there is a reason that some ?(not sure how many?) claim the 7K is "deaf" on VHF/UHF. ?But it doesn't seem to be inherent in the design. ?One of my radios is circa 2006, the other 2010. ?Both have almost identical RX performance on all bands as delivered from the factory (except one is a little soft on 6M on the analyzer). Without comparing a deaf radio to one that meets spec on an analyzer, I can't say much more. ?I spent about ten years of my career doing formal product evaluations of new computer system designs prior to release to manufacturing, so I try to be objective in my opinions and use accurate data whenever possible. I still encourage you to have your radio tested on a calibrated analyzer. ?Usually one of the local repeater trustees or radio clubs can put you in touch with someone. ?Like I said in an earlier post, the only radios I've tested that didn't meet spec had obviously been damaged due to lightning, since there were multiple components that had to be replaced in the front end. ?They still received, but were down about 15-20+ dB on VHF & UHF. ?Many hams don't have surge suppressors and good grounding on their VHF/UHF base antennas and even fewer protect their mobile installations. ?A strike that is thousands of feet away can still generate enough EMF to weaken the FET's used in the front end. ?It punches through the gate dielectric enough to reduce the gain but not fry the part. Steve, W3AHL |
n2gyn
Steve W3AHL