AR3000 - deaf on VHF vs AR5000 etc??

g8tzl2004

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I have acquired an original AR3000 (NOT the "A" version)

I was expecting to have to replace the lithium battery...but it was OK!!!

The AR3000 was initially completely deaf on HF (100 KHz - 30 MHz)....but this was because the HF pre-amp had been switched off. There was NO mention of the HF pre-amp in the AR3000 manual and only a few brief comments on the internet...but enough for me to figure out that I needed to move both internal switches to the ON position...and the HF band then came to life :)

On VHF Airband the radio is OK...and only a few dB's below my other stuff... I compared it with my ham stuff and an Icom R20 and it worked OK.

But on VHF 136 - 175 MHz, the AR3000 is about 10-15dB below my other stuff, especially on 144-148 MHz. I was expecting the AR3000 to be, say, 5dB less sensitive than my ham stuff and my Icom R20....but not 10-15dB down. The AR3000 VHF RX sensitivity is transformed when I use an external 10-20dB pre-amp.

I checked out an AR3000A service manual (I could not find a AR3000 SM) and the alignment details stated that sensitivity at 128.9 MHz should be at least -6dBu for 12dB SINAD....which is 0.5uV or -113dBm...so my other radio stuff is about 10dB better than the official specs....but real world specs are usually better than the official worst case specs (in my experience).

I don't think that there is any VHF 136 - 175 MHz internal pre-amp that I can switch on....and VHF airband seems to be OK..so maybe the AR3000's band pass filters for VHF 136 - 175 MHz are out of alignment??

Any views on the VHF 136 - 175 MHz RX sensitivity of an original AR3000? How should an AR3000 compare with an Icom R20 and an AR5000 on VHF. Is an AR3000 noticeably deafer or are the BPF's on my AR3000 out of alignment?
 
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marlbrook

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Since efficiency was down on HF too, personally the first area I would suspect is the BNC socket. Use contact cleaner on both the socket and the plug you are using, physically inserting and removing the plug several times.

Sounds too simple? Perhaps, but an all but invisible bit of corrosion on/in an Antenna BNC plug or socket can have devastating results on performance.
 

g8tzl2004

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OK on cleaning the BNC socket.

HF was originally down as to the internal HF pre-amp was switched off....there are 2 internal switches and both need to be ON. To correctly switch OFF the pre-amp, both switches need to be OFF. One of my switches was OFF and the other was ON...I'm not sure whether this made my AR3000 "completely" deaf on HF....as both switches should be OFF if an full sized external HF antenna is used which will overload the AR3000....but when both switches were ON, HF was back to life using a small HF antenna wire antenna.

I checked out the AR3000 again on airband...while an external 10-15dB pre-amp made NO difference with the Icom R20 and a real Icom airband handheld...as both already had enough front end gain...the external pre-amp DID improve the sensitivity of the AR3000....so the AR3000 is down on airband as well as VHF.

My conclusion is that the AR3000 is 10 - 15dB down above 30MHz..but is this "normal"?? The AR3000A (note the "A") spec is 0.35uV (-116dBm) for 12dB SINAD...compared to, say, 0.14 (-124dBm) for my ham stuff...I don't have any AR3000 sensitivity specs, but I assume its similar to the AR3000A. Some top end professional AOR stuff has really poor 12dB SINAD spec as the radio is built for selectivity rather than sensitivity...but I doubt this is the case with the AR3000. So maybe the AR3000's front end internal RF amp is dead?
 

marlbrook

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I have the 3000 and 3000A. Mine are certainly not insensitive. You will no doubt find many very positive posts about both.

If the BNC cleaning does not do the trick, I think you are correct and it is possibly the front end RF amp.

Just in case, do a full factory reset though.

Good luck.
 

g8tzl2004

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Marlbrook - does the 3000 and 3000A have identical RF performance? I only have the 3000A service manual...but I'm assuming that the RF side of the radios are more or less identical...although I read that a different CPU is used.

There are 3 RF amps in the AR3000 for 100KHz-30MHz, 30 - 940 MHz and 940 - 2000 MHZ.

I did a RF front end gain test at the 940 MHz switching threshold....ie moving from 939.999 MHz to 940.0000 MHz switches in a different RF amp....and at 939.999 MHz the AR3000 is about 10-15dB deafer than at 940 MHz. So my conclusion is that the 30 - 940 MHZ RF amp has failed :( I used an inline variable external -10 to +20dB pre-amp to confirm the results. With an external 10dB of pre-amplification, the AR3000 works great on 30 - 940 MHz :)

Marlbrook..please can you check that there is NO significant increase in gain between 939.999 and 940 MHz on your AR3000. Listen in AM mode with an antenna connected and the background noise should be about the same. At my QTH there is a cell phone signal spreading across 940 MHz so its easy to see the big jump in signal as the 939.999/940 threshold is crossed...thereby proving that the RF gain at 939.999 MHz is about 10dB less than at 940 MHz.

I will also try resetting the CPU in case there is some RF amp switching issue.

The RF front end comprises a 2SC3585 and a FET 2SK571 (base on the AR3000A SM). I'm guessing that the FET has failed. Has anybody replaced the RF front end devices in an AR3000? Was it easy or difficult? Is it easily accessible?
 

g8tzl2004

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I have checked the schematics and it appears that the 940 - 2036 MHz range uses two 2SK571 amps...each or which provides around 10dB of gain ( I think)..so that's around 20dB of gain in total vs one 2SK571 device in the 30 - 940 MHZ range and just 10dB of gain.

So in theory there should be a 10dB increase in gain when switching from 939.9999 to 940 MHz in a fully functioning AR3000. In my case, assuming that the 2SK571 device for 30 - 934 MHz is dead in my AR3000, then I should see a 20dB increase in gain when I jump from 939.9999 to 940 MHz.

I checked out a Monitoring Times review of the AR3000A which provides a sensitivity graph for 12dB SINAD. Extracting data from the graph, it appears that the AR3000 sensitivity at 850 (0.44uV/-114dBm) and 900 (0.36uV/-116dBm) jumps to 0.15uV/-123dBm at 940 MHz....so this proves that there is a 7-9dBm jump in sensitivity at the 939.999/940 MHz threshold....which fits with the assumed additional10dB of gain provided by the extra 2SK571 device??

As I am assuming the 2SK571 device in my AR3000 for 30 - 940 MHz is dead, then I should see a 20dB jump in sensitivity at the 939.999/940 MHz threshold.....and this is in fact the case. Using a variable external preamp. I need around 20dB of extra gain at 939.999 to get the same strength signal as a signal on 940 MHz. Conclusion - I need to replace the 2SK571 device for the 30 - 940 MHz range :(
 

marlbrook

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My 3000 and 3000A are mothballed at present, all my time has been taken up writing the program for the AR-DV1. I was relying on my memory when the 3000/A were getting a lot of use. At the time I had several other makes of Scanner, and both AOR devices were on a par with those across their range. Cheers
 

g8tzl2004

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Or maybe the 2SC3585 device has failed...as this comes before the 2SK571 device and also provides around 9 or 10dB of gain??
 

g8tzl2004

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The ATT is not turned on...and as the AR3000 is deaf across 30 - 940 MHz (but sensitive above 940 MHz), I guess its not a specific band pass filter issue as 30 -940 MHz includes several different BPF's not just one (I initially thought that airband was OK but it is 10dB down)?

I also initially thought that the memory back up battery was OK...but its not working :( I read that with the AR3000A, the radio will NOT boot up if the memory backup battery is dead. My radio boots OK...but resets if the AR3000 has been disconnected from the PSU overnight. I think early AR3000's used a small rechargeable battery for memory backup rather than a lithium CR2032 button battery. I guess the rechargeable battery is NOT retaining a charge for more than a few hours..so if the AR3000 is not powered overnight, the radio resets...but there is still a trickle charge voltage supplied to the rechargeable battery so the radio boots up OK?

When I power down my AR3000, the clock is displayed on the LCD with NO power to the radio..so I guess the backup battery was used to power the clock as well as memory retention?
 

marlbrook

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I have had to replace the backup battery. Yours is not quite dead I assume, as usually the radio will not boot if the battery is totally dead. I have done this on the 3000 and 3000A but I cannot remember the details now.

I do remember I found it easier just to cut the battery connectors, and solder a new one on to them, rather than un-soldering from the PCB.

It is worth noting that after replacing a battery you are supposed to preform a factory reset. If not the 3000 can exhibit odd behaviour. I know that was true in my case. As your battery is dying overnight, then until replaced you cannot be sure that the firmware is working totally correctly at any time.

That may have no bearing on your other issues I realise. Did you thoroughly clean the BNC socket by the way. In the past when I have suggested this some people decided it could not be causing any problems, until finally in desperation they tried it, and 'learned', lol. They may appear clean to the naked eye, but even a tiny amount of corrosion can have bad results to sensitivity.
 
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g8tzl2004

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Yes I cleaned the BNC with some switch cleaner..it was surprising how much black "carbon" stuff came out...but the AR3000 is still deaf across 30 - 940 MHz.

There are 3 separate RF amps in the AR3000 : 100KHz - 30MHz, 30 - 940 and 940 - 2000 MHz. In my AR3000, the radio is only deaf in the 30 - 940 MHz segment. In AM mode, its possible to hear the increase in gain as the radio switches RF amps as you tune from 939.999 MHz ( ie dead RF amp) to 940 MHz (ie good RF amp).

I read that early AR3000's used rechargeable memory batteries. The clock on my AR3000 stays on when you cut the power. I assume that is why a rechargeable battery was used. If a CR2032 was used, then it would be necessary to change the battery every 2 years :) I guess there is a trickle charge voltage supplying the rechargeable battery so that enables the radio to boot OK.

Does the clock stay on when you cut the power on your AR3000? I guess that later firmware did not keep the clock on to save the battery after the rechargeable battery was replaced with a soldered in CR2032? I wonder who decided to put it in such a difficult to reach place? AOR could also have just used a CR2032 holder so that it would have been easy to replace batteries...but then they probably thought that it would only be necessary to replace batteries every 20 years :)

When I power up after the radio has been switched off overnight, the radio completely resets itself with all the LCD segments displayed and the radio defaults to 80 MHz WFM.

AOR UK's website used to have lots of useful mod info on the AR3000...but the UK website is no longer operational. I think I read that somebody had created another website to retain all the useful info...but I can't find it. Anybody know where I might find it?
 

marlbrook

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Sorry I do not remember exactly what happened with the AR3000 battery.

I will send you a PM with a link to my Server, and all the files I have on record about both Radios.
 

marlbrook

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One other thing worth trying perhaps. With the top of the case removed, locate the back of the BNC socket, and attach a wire to the centre pin from the rear, to act as an aerial etc. , or something similar. Is there a leap in background noise/ 'S' reading that you do not get if attaching an antenna from the outside of the socket?

I would also follow the centre pin connector to the PCB and check there too. You may be right that a component has failed, however fully eliminating any problem with the aerial input physically is the first step I would take.
 

g8tzl2004

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Thanks very much for the files you have...its much appreciated.

OK on the BNC socket. The AR3000 works OK on an external antenna above 940 MHz and below 30 MHz..so I guess the BNC is OK. Above 940 and below 30 MHz the AR3000 uses different RF amps.

I also read in the service manual that there is NO band pass filter adjustment until above 108 MHz. The BPF's between 30 - 108 MHz use fixed values The RF amp which I am thinking has failed operates between 30 - 940 MHz...so in theory the AR3000 should be about 10dB deafer between 30 - 940 MHz. I've been doing some preliminary experimenting between 30 - 108 MHz...and I'm wondering if sensitivity is OK ...I can hear a 50 MHz beacon as well on the AR3000 as my Icom R20..and also Band 2 FM stations. I really need a weak signal to do an accurate test...but maybe the problem is band pass filter alignment between 108 and 940 MHz??
 

marlbrook

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In an earlier post you said the 3000 was deaf over a certain frequency range. I assumed you meant it picked up nothing at all, but from your last post that does not seem to be the case.

How were/are you determining the 'deafness'? A lower 'S' reading on the meter compared to another Receiver, or barely any acknowledgement the signal is present?

Re. the BNC socket, personally I would not 'guess' it must be OK, when once the case is open it is a simple operation just to add an antenna to the inside of the pin. It may be fine, but if corroded inside that will produce different results across the entire frequency range. I won't mention it again, lol, but it sounds as if you may be considering attacking the RF side of the PCB's at some stage, and where the antenna connects to it could be too easy to ignore when steeling oneself for major surgery.

By the way I like your commitment to getting the AR3000 up and running.
 
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g8tzl2004

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By "deaf", I mean less sensitive than you would expect...in the case of my AR3000 its about 10dB down. So compared with my other radios, on VHF, a weak but copyable signal on eg an Icom R20, is in the noise and difficult to copy on the AR3000. If I connect an external 10dB pre-amp to the AR3000, sensitivity is then about the same as the R20. I am judging sensitivity on the ability to copy a weak signal and not the reading on the signal strength meter as all meters are different :)

The AR3000 uses a different RF amp at 940 - 2000 MHz..so at 939.9999 MHz the radio is deaf but a really small change in frequency to 940.0000 MHz results in a big 20dB increase in RF "noise" as the "working" RF amp is switched in. So my conclusion is that its probably the AR3000's 30 - 940 MHz RF amp...OR some issue with the BPF's :) Maybe the previous owner had been messing with a screwdriver :) The previous owner had switched off the HF pre-amp so maybe he was using an "active antenna"...and maybe he was getting VHF pager breakthrough so detuned the AR3000 VHF band pass filters to try and solve the problem...who knows???
 

marlbrook

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In an earlier post you said the 3000 was deaf over a certain frequency range. I assumed you meant it picked up nothing at all, but from your last post that does not seem to be the case.

How were/are you determining the 'deafness'? A lower 'S' reading on the meter compared to another Receiver, or barely any acknowledgement the signal is present?
 

marlbrook

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Understood. Are you going to repair it yourself, or just use the external preamp? In any case, best of luck.

As I recall AOR will no longer repair the 3000 series.
 

g8tzl2004

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I want to repair the AR3000 myself. I'm tempted to swap the RF amp device (2SK571) used on 940 - 2000MHz which is the same device as used on 30 - 940 MHz...but its probably best to source a new replacement. Its a pity AOR UK closed down as it was run by really helpful people. There was a You Tube video of another AOR model where the front end had blown and it had previously been repaired by a dealer...it looked like a hot nail had been used instead of a soldering iron :)
 
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