FM900 Series

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FM900 Series

Post by RF-Bot » Tue Apr 24, 2018 11:05 pm

Submitted By: Jason.


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When I started to get interested in radio, the Philips FM900 series of two way radios were pretty much the latest thing. Nowadays, these radios are getting a little long in the tooth, but still perform very well when stacked up against the latest and greatest.

There are plenty of second hand FM900s out there on the second hand market, which appeal to those who want something a little bit different for their amateur or UHF CB station. So, the time is ripe to have another look over the FM900.

Before diving into the review, a little bit of history of the radio. Back in 1982, Philips TMC had designed the FM900 series radio as a replacement for the good 'ol FM828, a crystal driven, no scanning, but exceptionally reliable radio. The radio was squarely aimed at the commercial and fleet markets, and had the quality and price to match. These days, the quality is still there, but the price has dropped so much that it is affordable by anyone on a budget.

The FM900 radios came in several flavours, but the most common were the FM91, FM92 and FM93. The FM91 was the remote control head, all features, 120 channels top-of-the-line model, followed by the remote control head FM92, with fewer features, 99 channels, and simpler to drive, and the FM93, a one piece radio with features the same as the FM92 but only 10 channels. There were several options, too, such as being able to order CTCSS, SelCall, a temperature controlled crystal oscillator, voting, etc etc.

The choice radio is, of course, the FM91, which as mentioned before is programmable for 120 channels, can have 3 pre-defined pre-programmed scan banks, another 2 operator selectable scan banks where you choose what channels you want to scan, variable output power of 1, 5 or 25 Watts, variable SelCall sending and receiving and variable CTCSS encode and decode. There are digital up/down type controls for volume and mute levels. Voting is also an option if that is your thing. The control head of the radio has many buttons to keep the incurable button pusher happy, and an eight digit display that shows channel number, SelCall numbers, power output level selection and a whole multitude of other items, depending on the options you have installed or programmed. The body of the radio is different from the FM92 in that the transmitter board is given it's own little section, separate from the rest of the radio body, with a larger heatsink than the FM92. Quite an advanced radio for it's day.

The FM92 is probably the more common of the FM900 series you will encounter. It too has a remote head and body configuration, but the head has fewer controls, a 2 digit display, and unlike the FM91, has an inbuilt (although somewhat tinny sounding) speaker and the more common 'pot' controls for volume and mute. With 99 channels on call, 2 pre-defined scan groups, non-variable CTCSS and SelCall, power output that can be programmed differently for each channel, but is not user selectable, it has less features than the flagship FM91, and thus attracted a lower price tag. It was still built to the same high quality specification as the rest of the FM900 series, however.

The FM93 is essentially a FM92 in the more conventional single piece unit, but with 10 channels only.

All the radios featured a display that could blank itself after a short period of time, or even switch the whole radio off after 8 hours of no activity, a mute that could be configured in several ways, a feature that could cut down on the current consumption when idle, a transmit time-out timer, and scanning. Option boards that were add on's included CTCSS, SelCall, and some versions were fitted with an ignition noise blanker or higher stability reference crystal oscillator options. In addition to this, all the radios featured a very good receiver which is quite immune to adjacent channel problems probably due to the twin crystal filters, and a proven design transmitter that is low in harmonic output. I must say that I am very impressed by the receiver in the FM900s - they may not be the outright most sensitive receiver I have seen, but they are very resistant to adjacent channel bleed over. For example, one high powered station only 500 metres and 50 KHz away from where I operate my FM91 goes completely un-noticed.

All the FM900 radios had their channel information and options etc. programmed onto an EPROM. All the channel and frequency information resides there, as well as the pre-defined scan group channels, and CTCSS parameters. In fact, practically the whole radios 'personality' is stored on the EPROM. If you need to make changes to your radio, all that is required is for you to remove the EPROM and insert a new one containing the updated data. The data for the EPROM is created using a Philips specific piece of software called FPP, which any two way radio service shop would have. All you would have to do is explain your requirements to them, and they will do the rest for you and hand over a new EPROM, programmed to your specific needs.

Another item that makes the FM900s an attractive proposition for the hobbyist is that serviceability is good. Internal construction consisted mainly of discrete componentry, with surface mount items only used in the modular sections that you would normally replace as a whole, such as the VCO, or microphone audio board and so on. Admittedly, some of these modules are now becoming hard to find, but it is nice to know that they can be replaced easily if you have to.

As for physical construction of the radio, the best term I would use to describe the FM900s would be 'over engineered'. The body of the radio is made of a solid diecast chassis, with very robust steel plate covers, and a very strong cradle to hold the body to whatever surface you want. The rugged design doesn't end there, either. Critical items such as the VCO sit inside a steel 'can' which is held against the chassis. This is done to prevent 'microphony' of the VCO and to act as a total screen to noise. Further shielding is evident on the front end amplifier and filter module, with the synthesiser, and computer control sections of the radio also receiving their own shielding. Of course, the transmitter is very well shielded from the rest of the radio, with the FM91 having the transmitter separated from the rest of the body as noted above. Even the remote head on those models that have it, is quite robust. Some people do not like the design because of this overkill in engineering, but I think better too much than too little.

Being of conventional design (ie not surface mount) also lends the radio to easy modifications, if required. An example is that the rather loud beep that accompanies each key press can be either reduced or removed all together. Another modification sees the standard microphone being replaced with another that allows a more natural voice quality. If you have access to the Internet, a web page details some modifications, Look up here.

In short, then, the FM900 series of radios are quite affordable on the second hand market these days, although this depends on where you look, and the FM91 and 92 especially make excellent base stations or mobile units if you have the room. Many are in use on the 2 metre band, as well as a few UHF CB. They are ideal for those who want to use them for their respective hobby, but may also want to have access to a commercial two way frequency that they are licensed for (of course!) or for a few 'receive only' channels in or around the same band. My own FM91 may look a little the worse for wear, but it is still performing as strongly as it was the day it came from the factory, and that, folks, speaks volumes of just how reliable and well built the FM900s are.

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