Showing posts with label aa4oo. Show all posts
Showing posts with label aa4oo. Show all posts

Friday, March 19, 2021

The Endurance of CW in Amateur Radio

CW Spans a Century

I've enjoyed using my "new" GRC-9 radio for making CW and AM contacts over the past month.  During that time I've also discovered https://worldradiohistory.com/Archive-Radio-News/ which has magazine articles about radio dating back to 1919.  Reading about amateur operators building and using equipment at the time where CW (continuous wave) was beginning to replace spark-gap operation in wireless communication made me consider just how enduring the ability to communicate using CW and AM have been. 

Prior to the introduction of continuous wave transmitters and receivers, the detector used for spark gap communication would have made it difficult to hear a CW transmission (lacking a BFO). So, even though wireless transmission and reception of International Morse Code dates back earlier than 1919; employing CW (continuous wave) to send Morse Code seems to have began its popularity around that time.  AM (amplitude modulation) phone mode was also in use at the time, and grew in popularity during the 40's and 50's until more efficient voice modes overtook it in popularity for voice communication.



Radio Telegrapher School for Enlisted Specialists 1921


What other modes have remained as popular standards using standard ham equipment and continuously in use by amateur radio operators as CW?

My GRC-9 was designed near the end of WW2 (circa 1945), and was in continuous production for various armed forces around the world until around 1974 (3 decades is a long production run).  My particular unit has a receiver manufactured by Telefunken in 1955 and a Lewyt manufactured transmitter from 1966.  I have made CW and AM QSOs with other amateur radio operators whose equipment ranged from home-brew xmtr/rcvrs, Drake and Collins radios as well as shiny new Icom 7300 and Flex radio systems.  

A modern amateur radio (typically a HF model) can be used to communicate with radios built 100 years in the past. The same might be said for AM fone (phone), but that mode has become a niche for a much smaller set of enthusiasts.

There are lots of new and exciting modes of communication in amateur radio.  Many are pushing the boundaries of weak signal reception, or alternatively allow for high transfer rates of data. But it is somehow comforting to me to consider that amateur radio hobbyists have kept one mode in particular, CW, popular and in continuous use for over 100 years using equipment that remains compatible to communicate with one another.  I wonder if that will be the case in another century?

That's all for now, so lower your power and raise your expectations

Richard, AA4OO

Sunday, January 24, 2021

AN/GRC-9 aka "Angry Nine"

 AN/GRC-9 - Long lived military comms

My lovely (and radioactive) RT/77-GRC/9

Video summary




I don't recall where I first read about the Angry Nine, but it captured my imagination.  I read everything I could find about them and decided it would be great fun to operate such an antique on the ham bands.   There is no logical reason to desire such a QRP radio.  The low power output on CW is indeed, 5 watts and high power is a pileup busting 15 watts.   The AM transmission are 1 watt and 7 watts respectively.  That's almost QRPp for AM mode.

I'd had some experience restoring old tube equipment; my Heathkit HW-101, Knightkits VFO and Hallicrafters keyer, and I figured I'd take the next plunge and learn to use a receiver-transmitter combination and see how mobile high-voltage power worked from Vibrators and Dynamotors.   

These radios seemed to have been more plentiful in the surplus market 10 - 20 years ago.  Now you'll occasionally see one come up on eBay or other sites, but often times they are in very rough shape or the they are foreign language versions.  I bid on a few auctions over the past couple of years and the bidding always exceeded my threshold for what I thought it was worth.  The one above was part of an auction from an individual who had actually trained on these units prior to deploying to Vietnam.  Later in life he became interested in finding one and spent time in military surplus warehouses going through pallets of equipment to find one in good shape.  This particular unit is made up of a Lewyt manufactured transmitter and a Telefunken receiver.  The original owner preferred the receiver characteristics of the Telefunken over the Lewyt manufactured model, so he paired the two.

Many of these old units are radioactive, due to the radium paint used on the front panels to make the lettering glow in the dark.  This particular unit is off the lower scale on the Geiger counter and must be handled with care.  Basically, I have to be careful to not touch my face with my hands after operating the unit and wash my hands thoroughly.  Radium emits Alpha particles, which are not especially strong but the resultant radioactive dust from the front panel shouldn't be breathed or ingested. I plan to paint a clear-coat over the remaining lettering to lessen the Alpha particle emissions..  

Hot receiver, in more ways than one


The AN/GRC-9 is a set of components primarily comprised of the RT-77/GRC-9 receiver-transmitter, capable of operating between 2-12 MHz in CW, MCW and AM modes.  MCW is a modulated form of CW that can be received by radios that do not have a BFO (i.e. a normal AM receiver).  

It is a mid to late 1940's design and was first documented field use in the Korean War, and was in active use through the Vietnam War and continued to be maintained in US military warehouses until 1974.  It was in use by other nations long after, most notably the Dutch military.

Out of the case, tracing a low B+ power problem



Power on the move

Designed to be used in the field, both vehicle mounted and carried by mobile infantry; there were a number of ways to supply power to the unit.  There were a few different Vibrator/Dynamotor units, that could operate from common DC voltages of the time (6v, 12v, 24v) as well as a hand cranked, field portable generator.

Keep in mind that the state of the art at the time of its design used vacuum tube technology and in the case of the RT/77-GRC/9 it required the following voltages:
  • Transmitter Plates -- 475 - 580 v @  100ma
  • Transmitter Filaments -- 6.5 - 6.6 v@ 2 amps
  • Receiver Plates -- 105 - 120 v @ 45ma
  • Receiver  Filaments -- 1.35 - 1.5 v @ 500ma
  • Keying Relay -- 6.0 - 6.9 v @ 575ma

That's a tall order for mobile and portable power supplies but designers in the 1940's were quite clever in packing power supply units.   I managed to obtain both the hand cranked GN-58 generator with the base chassis and seat for portable operations, and a DY-88 for fixed / mobile operations.  


DY-88 mobile power supply

DY-88 set to 12v powered by Amateur 12v supply

Vibrator power supply for low B+

Power filtering

I supply the DY-88 from either an RV battery or an amateur 12v power supply.  When in Standby the DY-88 draws less than 1 amp, but placing the radio in Send mode switches on the Dynamotor which draws 12 amps @12v, without key-down and up to 14 amps on high-output key-down.  It will drain an RV battery pretty quickly at that rate if the radio is left in Send mode, and works an amateur power supply pretty hard as well.  So don't expect to operate remote off a battery alone for too long if your having lengthy QSOs.  An added benefit of the DY-88 is that when the enclosed Dynamotor is running you'll have a nice extra 85 dB of generator noise to accompany your listening pleasure.


GN-58 portable field hand-cranked power supply

Generator head in carry bag

Unmounted as seen from the bottom

On the stand with cover and handles disconnected



Deployed


The GN-58 is a tough workout since it has to be cranked by hand at 60 rpm continuously.  Obviously, you need a partner unless you can figure out how to crank it with your feet while sending CW. You will also want that partner to help you carry the GN-58, and the accompanying accessory bag for the chassis and seat.  IT'S HEAVY.  I haven't weighed everything, but according to the manual that came with the set, the radio / generator / accessories including antennas comes out around 120 lbs.  

If you have a BA-48 battery hooked up then your human power supply can pause cranking while your receiving.  I have a BA-48 battery enclosure that has been gutted of the original, long-dead material and replaced with 10x 9v batteries in series for the low B+ and two D-Cell batteries in parallel for the receiver filament supply.


Accessories



Bag of goodies

The radio itself has a carry bag, as well as a bag for the GN-58 legs and seat, the vertical antenna, and miscellaneous.

There's another bag (shown above) for carrying power supply cables, keys, hand mic, long wire and doublet antennas, external speaker, torture device headphones, torture device in-ear phones, as well as a box of spare tubes for the radio.

If you're traveling in a squad sized group, then many hands make light work, otherwise you're going to be making a lot of trips hauling your QRP rig up the hill.

Headphones

These Western Electric headphones clamp tightly over your ears sealing out QRM and squeezing your head like a vice.  After 10 minutes I was confessing to sins I'd never committed. 








In order to use the headphones the RT/77 receiver must be removed from the case and an impedance switch on the back, changed from 4000 to 250 using a screwdriver.  The ham I bought my set from had constructed a CW audio filter along with an impedance switch on an outboard box, that allowed the use of the headphones without switching the impedance on the receiver unit.

Homebuilt CW filter with impedance switch

Speaker


The external speaker is a rugged, high impedance device (4k Ohms), that after all these years can still output audio at high volumes without distortion.  It has a built in thumbscrew clamp that allows it to be attached to vertical or horizontal objects.

Alternately, the thumbscrew can be used in combination with the vice-like headphones to extract information from a prisoner.

Antennas

The AN/GRC-9 comes with 3 antenna systems; a multiple section, whip vertical for quick field setup and mobile use, a long wire that can be quickly deployed in a fixed station as a sloper, and a doublet for best reception, transmission in a fixed location.



For testing purposes I have my radio hooked up to my 80m Windom, which it tunes very nicely on 80m, 60m, 40m and 10m bands. 

When the weather warms a bit I will be taking the radio out for some portable use and I'll try it out with the antennas that are part of the AN/GRC-9 set.

Spares

As a military radio, it was expected that repairs should be performed in the field when possible.  The radio shipped with spare tubes for the receiver-transmitter, as well as spare tubes and vibrators for the DY-88 power supply.


More to come

In the few days I've had the AN/GRC-9 the only problems I've encountered have been related to the old DY-88 power supply.  Old vibrators cans are generally seized up, as was the case with mine.  Eventually mine became un-stuck after repeated applications of power but there are some methods to restore truly frozen ones using AC current and light bulbs (see Notes section below).

I've made about half a dozen contacts on the ham bands, including a 40m contact to a station in TX which is kinda DX for my locale.  I've received nice signal reports.  I've specifically asked stations about my "chirp" during QSOs and they've reported it as "not bad" and "charming".  When operating from the VFO (master oscillator) rather than a crystal, the GRC-9 will "chirp". It was considered an acceptable design trade-off at the time.  I've listened to the transmitter from a remote WebSDR station to hear the chirp for myself, and I agree that it isn't extreme and lends some character to the station.  The unit does drift about 200 Hz during a QSO which I also think is quite acceptable for it's age.  It's possible that if I spent more time in Send mode prior to a QSO to allow the transmitter tubes to warm up the drift might be lessened, but keeping the radio in Send mode puts quite a load on the power supply (both the 12v supplying the DY-88 and the human cranking the GN-58).

The RT-77 Telefunken receiver doesn't offer much in terms of selectivity and on a crowded band there's a lot of stations to contend with in the passband.  The outboard CW filter deals with this nicely, but it is so narrow that when shifting from Send to Standby, the resulting frequency shift often throws the station I'm receiving out of the filter's passband, so that's a bit tricky.

The receiver's tuning knob also is very coarse, in that fine adjustments are made by breathing on the knob.  However it has zero backlash, which is amazing in a piece of equipment this old.  The markings on the receiver are in 50 kHz intervals so the only way to really figure out where you are is to look at RBN for your spot.

50 kHz spacing when reading the frequency on the receiver
Note the 7.2 is 7.200 MHz in the 40m band


Images

Enjoy the pictures of the AN/GRC-9













Phosphor glowing nicely on the GRC-9
As opposed to the degraded glow of the radium infused lettering on the RT-77 half









That's all for now

73

So go heavyweight for you QRP station to get your excercise.

DE AA4OO


Notes

Instructions for restoring a vibrator to operation

Instructions posted by:
Robert
Gunner
USN Retired
MVPA 9480

VB-1 and VB-7 are interchangable. I think I recall reading somewhere that VB-7 is a "lightweight" version of VB-1 but I won't swear to that.

The base is 4-pin, and the pin numbers are counted as on a vacuum tube with the same base. I wish I could post an image here without uploading it somewhere but if it's possible I've not figured out how to do it. The pins count clockwise from 1 to 4 looking at the bottom of the vibrator or the wiring side of the socket. The two large pins are 4 and 1 and the two small ones are 2 and 3.

There are two basic types of vibrators, called Series and Shunt. The Series type has a contact in series with the coil. VB-1, 7 and 16 are all Series types. I'll skip the Shunt type for now.

Pin 1 is common. Pin 4 is coil. Pin 2 is the NO (Normally Open) switching contact and Pin 3 is NC (Normally Closed). To test a VB-1/7, use an ohmmeter to check continuity from 1 to 4. If the reading is infinity, the coil could be open but this seldom happens. The problem is probably the vibrator contact. If the reading is a few ohms, connect +6 VDC to Pin 4 and -6 VDC to Pin 1. The vibrator should run. If it doesn't, most likely the contact is welded. About the only solution is to open up the vibrator, unstick the contact and try to burnish the burn marks out of the contact.

If the vibrator does run, go to the end of this screed and do the final test.

If the reading is infinity, here's how to use the two or three lamps to (usually) fix the vibrator. SAFETY NOTE: bear in mind you are dealing with either 120 or 220 VAC. If you jury rig the hookup, do all of your connections and disconnections with the "rig" not connected to the AC line. In other words, don't touch anything except the plug on the line cord or (if you go to that much trouble) the ON-OFF switch when the line cord is plugged in.

Connect the hot side of the AC line cord to one side of both lamps. Connect the ground side of the AC line cord to Pin 1 of the vibrator (or socket if you use one). Connect the other side of one of the lamps to Pin 4 and the other lamp to Pins 3 and 2. If you splurge and use three lamps, connect the "cold" side of the second and third lamps to Pins 2 and 3 respectively.

Check all the wiring and when satisfied all is OK, plug in the line cord. Probably nothing will happen immediately. Within a few minutes to a few hours lamp 1 should begin flickering and you should hear the vibrator hum. Run the test until the second lamp begins to flicker or until both the 2nd and 3rd lamps flicker.

If you are only using two lamps, when the 2nd lamp begins to flicker, wait 1 or 2 minutes then remove power (unplug the line cord). Connect the 2nd lamp only to Pin 2 and plug in the line cord. If the 2nd lamp flickers, remove power, move the 2nd lamp connection to Pin 3 and apply power. In either case (with the 2nd lamp now connected to pin 2 or 3 only), let the test run until the 2nd lamp again flickers.

For a final test, connect one lamp to Pin 2 and one to Pin 3. Connect 6 VDC to Pins 4 and 1. With the vibrator vibrating apply power to the two lamps. They should flicker alternately. Note that for this test, either use a 6 volt battery or a 6 VDC supply with both outputs not grounded. I wouldn't try to use the battery in the Jeep just in case you mis-identify which side of the line cord is grounded and which is hot.

Although a vibrator that is going to be fixed by this procedure will usually begin to work after say no more than half an hour, I have seen it take several hours. So if I have one that didn't start working fairly quickly, I'll let the test run up to about 8 hours max (or overnight) before giving up.

Monday, April 9, 2018

Regulated voltage for Regenerative receiver project

Mr. Regula-tor

Building a regenerative tube receiver seems to have been a rite of passage for all hams of yesteryear.  Although I built one from a kit (4-States QRP) as my first electronics project a couple years ago I thought I'd go for the real deal and build a vacuum tube regen receiver.

I'm building a design based around the 6SN7 tube. While I'm collecting parts and still locating a suitable chassis I decided to build a regulated power supply from the parts I have.  Anyone familiar with electronics could probably whip this together in no time, but being the electronics newbie that I am, it is a slow process.

I'm using a transformer from a 1950's Heathkit VTVM V-7 that I parted out. It supplies the 6.3V filament voltage from one set of windings (yellow wires)  those tested good. But the HV was an unknown as it was only half wave rectified when the transformer was used in the meter.  That meter's rectifier and power cap had gone bad so I didn't know what condition the HV side of the transformer.

Breadboarded using a full wave rectifier created with 4 diodes, buffered by a 22uF electrolytic and a 10k resistor, I saw 189 volts, with no-load out of the high voltage side of the transformer. The amount of current the transformer could provide was still an unknown. I tested temporarily with a 2.5kOhm high wattage resistor and saw 56ma of current provided with a voltage sag down to 130V but the core of the transistor started heating up.  Within half an hour it was over 120F so I discontinued that load test.

Fortunately, the regen circuit uses a ridiculously small amount of current for B+; about 4 to 5mA. Although I will likely change the audio side of the tube to deliver enough current for a speaker rather than the high impedance headphones in the current design, which may potentially double that to 10ma.  For the first incarnation I'll stick with high-impedance headphones.

The regen power supply requirements called for 6.3V@0.5A and 90V@4mA B+.  The B+ voltage  was based on using 10x 9V batteries and it stated that voltage wasn't critical but shouldn't fall much below 90V, going 12% above 90V should be OK.

Generally batteries are used with regenerative receivers because they are so sensitive to power supply noise, but I wanted to give the power supply a shot first and if it proves too noisy I can fall back to battery power for the B+ and just use the filament voltage provided by this transformer.

Since I have a OB2 voltage regulation tube I want to use. The OB2 regulates at 108V so that's what I'm going with.  An OB3 would regulate at 90V, but I don't have one of those.


OB2 in action... Glow baby, Glow!

Calculating the resistor drop

A voltage regulating tube like a OB2 ionizes gas to maintain the voltage at the tube's specification.  In the case of an OB2 it tries to maintain voltage at 108V.  It requires a starting voltage higher than what it will regulate to, but ultimately can only dissipate so much current as it drops voltage.  So, a resistor must be put in series ahead of the VR tube to limit the current it will have to dissipate.  The resistor must be able to handle the current flowing through it, so that must be calculated as well.  

The calculation for the dropping resistor resistance is:
Rdrop = (Vs - Vreg) / (Ireg + Isupply)
So, in my case:
Voltage supply (Vs) = 189V
voltage regulation (Vreg) = 108V
regulator current (Ireg) the OB2 requires 5mA to do its job = 5mA
supply current (Isupply) the actual current required by the 6SN7 up to ~ 5mA

So, (189V - 108V) / (0.005A + 0.005A)  comes out to a resistor value of  10,100 ohms.  10k is the closest standard size resistor and at 108V it should be able to dissipate 1.166 watts.  So I'll need a 10k 2-watt resistor.

Parts is parts

Running the regulated power supply with a 10k Rdrop resistor for a few hours showed the transformer stabilize at 92F degrees at 70F amb.  I was using a separate 27k 2-watt resistor to simulate the ~4mA load that the receiver will draw at 108V. 

As you can see on the newly restored, trusty Heathkit VTVM; the voltage was holding steady around 108V.  With that little current, the OB2 is not visibly glowing but with the lights out the violet colored ionization is visible.



Summary

I'm going to order a larger filter capacitor.  The only one I had to test with was 22uF 360V and I'd like to use higher capacitance value of 47uF with a more appropriate voltage rating of 250V.  I will also be adding 0.01uF caps at the input and output of the filter capacitor and I may add a 0.01uF across the OB2 pins 1/7 to further attenuate any RF noise.   

With the current values I'm seeing 50mA ripple on my regulated voltage.

A bit over 50mA ripple

After I get the new capacitor and get the 0.01uF caps in play to filter out noise, I'll hook it up to the oscilloscope to check for ripple.  I'll update the post at that time.


That's all for now....

So lower your power the old fashioned way, using a voltage regulator tube.

72/73
Richard, AA4OO