Atlas

I recently purchased a used Atlas 210x transceiver. This particular radio has an IF of 5595 khz. I understand earlier radios had IFs of 5520 khz and later radios had IFs of 5645 khz. I have no idea as to why the IFs were changed from one series to another. I guess I really do not care. My particular radio appears to have a serial TH4976. Or maybe that is a date code. The 49th week in 1976?

I bought it because I have always wanted one of these little transceivers. These first came out in the early 1970’s They commanded a list price of $665. The base console/power supply was another $250. The VOX option was available for around $200. This radio has all three and cost me $170. Twenty dollars of that was for shipping.

It measures 9.5 inches wide, 7 inches deep, and 3.5 inches high. These measurements not including heat sink. The massive heatsink/final amp combination add another 2 inches to the depth dimension. It is small. Maybe even tiny by 1970 standards especially when you consider that it sports 5 ham bands and an OUTPUT power of 80 watts. Best of all it still works. Quite remarkable for a 37 year old radio. I suspect it really is only 20 years old but that does not make it any less remarkable.

There are a large amount of modifications published for this radio. Some of the mods are trivial, others are serious. None of them apply to my radio because it is of later manufacture.

The receiver is very basic using a diode ring first mixer and a diode ring product detector. No receiver rf amplifier. The antenna is connected directly to the mixer input after going through some double tuned input circuits. Single conversion, the IF is 5595 khz. Most of the gain is produced in the IF section. The audio output is an LM380 for about 2 watts maximum output to a three inch, 4 ohm speaker.

Sensitivity is better than .5 microvolts on all bands. IMD is around 80 db with weak signal performance at -130 db. Not as good as the best but far better than the worst.

The AC power supply in the console is of unusually clever design. It is about one third the size of and ICOM or Kenwood supply delivering the same power. The secret is that Atlas does not regulate the power to the final transistors. They are allowed to run open off whatever the transformer/fullwave diodes/capacitor filter section limits. Voltage to the finals is typically around 17 volts when run off the AC supply.

A second part of the supply is low current and regulated, but instead of using an expensive three terminal regulator, it used a cheap TO-220 power transistor with base biased to a 13 volt zener.

The back of the radio has two banana jacks for power. One is the higher current and the other is the lower current, regulated connection.

For mobile application both of these connections are connected in parallel and are run from the vehicle battery terminals.

It sports four plug-in printed circuit boards. The circuit board connectors are of high quality as is most of the mechanics of the radio. It looks good enough to meet military specifications.

The output is SWR protected. That feature protects the output transistors by reducing power if the SWR gets much above 2:1. At an SWR of 2:1 power is reduced to half maximum.

It is a very basic but nice radio. Audio quality is exceptional on receive and transmit because it uses a 2700khz filter. The filter has a 1.6 shape factor and extremely sharp skirts. This filter and the double tuned input circuits are the only selectivity related components in this radio but they appear to be more than adequate.

Although it will do CW it is primarily designed for SSB. It is also capable of increased power output by replacing the 50 volt final transistors with 80 volt units at a cost of 50 bucks or so. The output power then goes to about 117 watts on 80 meters with no need to modify the power supply.

I sure could have used this thing 20 years ago. Guess I will have to make up for lost time.

Explore posts in the same categories: HamRadio

3 Comments on “Atlas”

  1. admin Says:

    I finally figured out how to get it to work in CW mode. Hit upon the solution completely by accident. You have to unplug the microphone cable. After you do that, the transmitter will remain off when the CW function is selected if the key is open.

    Monitored the signal in the R4C. Not exactly chirpy. More of a whoop, whoop, but definately not pure tone. This was on 75 meters running 75 watts out to the all band dipole.

    Also had a QSO with NX7TT in Idaho this afternoon on 14.246. He reported a trace of hum, bassy sounding audio, and some frequency drift. Major frequency drift but from one transmission to another. It did not seem to drift during a transmission. Need to check regulators.

  2. Frank Says:

    Well, It definately has a frequency instability. Shows up when monitoring the signal. Monitoring on 75 meters with load adjusted for 65 watts output, monitor was a Drake R4C. Heard a shift in the signal while in CW mode. The shift was present when keying and when not keying. Evidently the VFO is not keyed but kept running and only the buffer or the finals are keyed.

    Anyway, while monitoring the frequency was shifting 200 maybe 300 hz up and down. These shifts were sudden, indicating that they were most likely caused by a voltage shift. Perhaps the regulated voltage is shifting due to intermittent load. Don’t know. Need to run more checks. Watching the voltage with a meter would be a good start.

  3. Frank Says:

    Took the covers off the console unit so that some voltage points could be monitored. Had to tilt the unit onto its back to gain access. Ended up putting the thing in CW mode with the key down. It stayed that way for some time until I discovered that the current meter was pegged to the right. Heat sink was ouchy hot and one of the power output transistors now has its base shorted to its collector.

    Ordered some 2SC2879 replacements from RF Parts. While I wait on those to arrive, I will see about installing the bias mod and the negative feedback mod.

    Failure symptoms were a dead radio with the meter pegged to the right. Same symptoms regardless of function switch setting. The bad transistor was taking the power supply to ground or close to it.


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