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AOR-2500 reviews

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"Ed Brown, KB1MZ Expert User AOR AR-2500 December 11, 1998 [This article was originally written April 26, 1994] The AR2500 appears to be built for AOR by Fairmate, who also makes the AR1000, and also sells it under their own model number of HP-100 (and HP-200 for the enhanced model). The AR1000 had mixed reviews, and lots of problems in their earlier units. Mine had a problem with poor sensitivity and being off frequency on the lower frequencies (I was able to cure this problem by re-adjusting the reference and 2nd l.o. crystal oscillators to the correct frequencies).

If it is as good a performer as the "real" AOR receivers, like the 2002, 2515, 3000, and their Regency MX5000/7000 series, then it is a bargain at 499.

ACE Communications is a good outfit, with speedy delivery, and a 25 day full refund policy, if the radio is defective or not up to expectation.

Now, how to fill those 2016 memory channels.....

The new AR-2500, made by Fairmate, for A.O.R. is a new wide range scanner, offering a lot of interesting features for a reasonable price. The AR2500 is a replacement for the AR2002 and the AR2515, which it supposedly duplicates, for a lower price. The AR2500 claims to have continuous coverage from 1 MHz to 1500 MHz, with AM, FM and WBFM modes, as well as a BFO for CW and SSB. The unit is one of the smallest scanners available, 2 1/4"H x 5 5/8"W x 6 1/2"D. and weighing about 14 ounces.

Compared to the earlier mentioned radios, which were built like tanks, the 2500 is on the light and flimsy side. Feels more like a toy. There are 62 banks of 32 channels each, plus another 16 search banks. Scan banks can be scanned separately, or linked together. Scan and search rates are fast, about 36 per second, if frequencies within a bank are kept reason- ably close together. Search increments are 5, 12.5 and 25 KHz.

There is a 9 pin type D connector on the rear panel for external computer control, and AOR has software available. The antenna connector is a BNC type, and there is a switchable attenuator. The AR2500 has a 9-segment LED signal strength meter, a feature not found on most scanners.

One of the first things that a user will notice is that the channels within a bank are not numbered, and that the AR2500 will sort the contents within a bank in descending frequency order. When a bank is full, the word "FULL" will appear on the display, and one or more of the old channels will have to be deleted. Operation of the 2500 is quite a bit different from most scanners, but is not difficult to master it.

The manual is written by ACE, and is well-written and easy to follow, but lacks in any real technical data about the radio. It covers in detail how to program and control the radio through the computer port. There are about seven pages listing the contents of all 2016 preprogrammed channels, which are all the commonly used public service frequencies in use in the USA. I ran a simple PC program through it and was able to load in frequency and mode, and make it search and store between two chosen frequencies, with the freq step computer selectable.

Enough description, now how does it perform?

I brought it into the lab and put it on a signal generator, to check out the sensitivity and make some meassurements in a nice "friendly" world where there are no strong signals to overload the front end, none of the usual noise and other electromagnetic garbage to cause confusion.

Sensitivity, under these ideal conditions, was surprisingly good, about .3 uV for AM and FM, and about 3 uV for WBFM, between 5 and 550 MHz, and 1 uV for AM and FM between 800 and 950 MHz, and slowly deteriorating up to 1300 MHz, where it fell to about 10 uV. In spite of the maunfacturer's claim of continuous coverage from 1 to 1500 MHz, my unit (serial number 10232) operated only from 1 to 550 and 800 - 1300 MHz. It will program anywhere from 0.000 to 1300 MHz, but is by no means "continuous coverage". Not a real loss, since 550 to 800 MHz is the UHF TV graveyard, and there isn't a whole lot of immediate interest from 1300 to 1500 MHz. The radio was slightly off frequency, but there is a simple adjustment to take care of this, which I'll get into later.

In the real world of RF pollution and strong signals, the AR2500's performance suffers somewhat, as we will soon see.

From 1 - 550 MHz, the first IF is 750 MHz, and the 2nd IF is 45.030 MHz, and, from 800 to 1300 MHz, the first IF is 45.030 MHz, with the LO on the low side. Image rejection in the 800 - 1300 MHz range is poor to outright terrible, varying from a modest 5 dB to -5dB (yes, the image is stronger than the intended signal). The images that appear are 90.060 MHz below the tuned frequency - so some of the upper UHF TV channels, such as 66 and 68 will decimate parts of the trunked radio (SMRS) and the cellular radio bands. Signals that are on or close to the 45.030 MHz IF will bleed through and override anything else that is tuned in. The NH State Police on 45.020 come in very well, no matter what frequency the AR2500 just happens to be tuned to at the time.

Such problems could exist due to poor shielding and filtering. Out of scientific curiosity, I carefully opened the radio to get a look inside. The only shielding was around the VCO part of the synthesizer, and that that was soldered up as tight as a copper kettle. Everything else was wide open, and exposed to any RF that happens by, whether from the antenna, through the plastic case, or internally generated by internal oscillators and by the logic circuitry.

The front end is definitely broad banded, with no pre-selection or real filtering. The 1 to 550 MHz signals pass through a simple LC low pass filter and go into an NEC5800 amplifier IC, and the 800 to 1300 MHz goes through an equally simple high-pass filter, into an NEC5805 IC, with no band pass filtering anywhere in sight. All the RF and analog circuitry is on a densely-packed double sided board, with extensive use of surface mount components. The logic and display circuitry are on two small, densely packed boards attached to the front panel. No user-repairable stuff here. Earlier, I said that the radio was slightly off frequency. The synthesizer reference crystal oscillator was slightly off, and is easily adjustable. I used a recently-calibrated signal generator, and carefully tweaked VC1, the trimmer capacitor, which is next to the reference crystal, X1, located just behind the front panel, on the main PC board.

The inclusion of 1 to 30 MHz is a nice addition, but it is by no means a serious HF receiver. The AM selectivity is intended for the VHF and UHF aircraft bands, with 25 KHz channels, so it is far too wide for proper SW reception. It does a passable job on the shortwave broadcast bands, but is a poor performer on SSB and CW reception. The BFO circuit is only a slight modernization of the BFO found in inexpensive 1950s vintage tube radios. I tried it on the 20 meter (14 MHz) ham band, and it just couldn't separate those crowded CW signals, and it also was seriously lacking on SSB.

From 30 to 550 MHz, the AR2500's sensitivity was equal to or better than my PRO2004, and R-7000. On 800 to 960 MHz, it was on a par with the 2004, and slightly less than the R7000. Sensitivity rolled off up to 1300, about the same amount as the PRO2004. The AR2500 was especially sensitive on the 118 - 137 and 225 - 400 MHz aircraft bands, clearly hearing signals that the 2004 and the R7000 could just barely detect. With a proper antenna, and some external band- pass filtering, it did an outstanding job, with good clear AM audio quality. The VHF low band (30 - 76 MHz) performance was good, except for the aforementioned 45.030 MHz IF bleedthrough problem. The LED signal strength meter measures approximately 5 dB per step, with .3 uV lighting the lowest (1st) LED, and about 30 uV lighting the top most (9th) LED. This gives around a 40 dB range for the meter.

Another problem begant to surface on my 2500: the tuning knob was becoming intermittent in the CCW direction, but was OK in the CW direction. The tuning knob is a simple "shaft encoder",and it was apparent that this was going bad.

I called ACE about the tuning knob problem, and about the non- continuous frequency coverage, and the person I talked with said that this was definitely defective, and that I should return it for either an exchange or a refund. I opted for the exchange, and wrote up a two page letter describing my observations, packed it back up and sent it via UPS back to ACE. Hopefully the replacement will arrive in the next week or two.

Strike Two

The second unit arrived in about 10 days. It also had the non-continuous coverage, though it was about 50 MHz "better". THe 45 MHz bleed through and the lack of image rejection on the 800 - 1300 MHz band were about the same. Sensitivity on the 800 - 1300 MHz band was much better. At this point the radio did everything that I wanted. Then, in less than three weeks, the < 550 MHz band went "deaf" by about 40 dB, but the 800 - 1300 was still fine. My SWAG was that the MC5800 front end chip died in an untimely fashion.

This unit went back to ACE, and at this time is languishing away, waiting to be repaired (ACE person said 4 to 6 weeks, and that there were currently no more 2500's available for replacement). I tried to pin them down on particulars, but the lady on the other end of the phone was polite, but vague, promising that their repair tech would call me the next day (he hasn't yet). I get the impression that there is a serious design problem with the 2500 and they are trying to fix it without calling too much attention to the fact. I'll gently nudge them about once a week until I get either the radio or my money back.

Maybe I should have saved up some more dough and gone for the AR3000...

Strike Three

I finally got the AR2500 back from ACE. The deaf <550 MHz problem was fixed (new 5800 IC, and they did some real schlocky/tacky ECO's in a feeble attempt to solve the squelch and 45.03 MHz IF bleedthru problems. They hung a couple transistors, resistors and some wires around the inside, and as a result, the squelch is a little better.

Then they stuck a wad of aluminum sticky tape over part of the VCO / Loop filter area, ostensibly as a shield. But there was NO contact with the ground foil, and in fact this "tent" was loose, rolling around the inside of the scanner like the proverbial loose cannon. Did I mention that the radio was dead on arrival? When I plugged it into the power pack, and turned it on, *NOTHING* happened. Dead as a rock. Nil. Nada.

After calming down, and deciding that a B-52 strike against ACE might be too extreme, I opened up the radio, and found that one of the plugs going to the front panel/control boards was not plugged in. I don't know if the ACE tech was in a hurry that day and overlooked this minor detail, or perhaps the UPS delivery crew had a little game of hackey-sack with my unit.

Anyway, I put the plug back in, removed that deadly little aluminum tape "time bomb" and tried again. This time, it worked. Better than before, but still far from perfect. In another feeble attempt to fix the hole between 550 and 800 MHz, they replaced the VCO assembly. This was apparent by the soldering iron burns and globs of flux around the area, that wasn't there before (I admit, I peeked). Now this gap is 600 to 790 MHz. Better, but still not to spec.

The tuning knob is still erratic at best in the CCW direction, giving random results. It works fine as long as I tune upwards in frequency. The 45 MHz bleedthru was still there, and the local NHSP Troop B on 45.020 comes thru loud and clear. No matter what frequency the 2500 just happens to be tuned to. I figured this out: It's not a bug, its a feature! Just like having a free priority channel! How clever of those AOR folks! Wow!

Another feature that I discovered was that the antenna didn't have to be actually connected securely to the BNC connector on the back. Just touching it to the outer shell of the BNC, or to the attenuator switch handle did the trick just fine. How clever! Further examination of this phenomenon disclosed that the outer shell of the BNC was not even connected to ground. Anywhere.

Anyway, I decided to bite the bullet, and see if I could solve some of these problems. First, I grounded the BNC shell. Better. I took a real plunge, and removed the cheap BNC and put in a mil-spec Amphenol BNC, and removed that pesky little attenuator switch and board, and wired the antenna jack directly to where it should go. Better yet! Next, I took some sticky-back copper foil and stuck it in the inside of the upper half of the plastic cabinet, and made a good solid contact to the BNC outer shell. This provided a bit of shielding, and kept the internally generated signals inside, and kept out most of the 45 MHz NHSP out of my IF strip. I know, the warranty's blown, but now it almost works as it should. Besides, I accomplished in an evening what ACE couldn't do in 10 weeks.

It does what I want it to do, in the main bands of interest (118 - 137 and 225 - 400 MHz). I can live with the hole in the UHF TV spectrum, and the very marginal HF/shortwave performance.

Would I do this again? No way, man."

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