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ARC-5 works great on AM...




 
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WB3JOK
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« Reply #100 on: February 15, 2015, 12:22:38 AM »

That is also what Tim 'QJE said... he saw the spectrum of another ARC-5 (couldn't recall whose, though) that was also missing most of the lower sideband. It would still takes a lot of incidental FM (or PM) to suppress it near-completely though. Maybe they do "all do that"!  Roll Eyes

This article was interesting reading:
http://ece.wpi.edu/analog/resources/hp-am-fm.pdf

(in particular, page 46 on asymmetrical sidebands).

Anyway I don't think I'm going to worry too much about it, since the signal sounds decent if I'm careful not to overmodulate (no ALC in this system), and I'm not about to add a buffer stage to an ARC-5 transmitter.
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VE3LYX
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« Reply #101 on: February 15, 2015, 09:18:50 AM »

Congratulations. I knew it was something minor. 
Mk19 AKA No 19 Wireless Set. (2 to 8mc low power transceiver with also a 235mc transceiver inside. Jeeps Tanks AFV and occasionally even the odd aircraft. 1940s to 1960s.)They were supposed to arrive yesterday by bus but have disappeared . Hopefully it is the weekend thing since they are bought and paid for. Will picture them when they arrive. I totally ignore SDR reports.  This mode is going to kill AM and all the fun. I just say thank you and move on.
don
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Don VE3LYX<br />Eng, DE & petite Francais
Steve - K4HX
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« Reply #102 on: February 15, 2015, 10:36:40 AM »

SDR is a mode? Who knew?
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WB3JOK
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« Reply #103 on: February 15, 2015, 10:56:14 AM »

Come on 'HX, you knew what he meant... "mode" as in what equipment he's operating, not the more specific definition of the type of RF emissions  Grin

I actually am interested to know what the output of my transmitter looks like in the frequency domain as well as the time domain. I don't have a spectrum analyzer with sufficiently narrow resolution to get a good look (min RBW on my HP 8557A is 1 KHz and there's a fair amount of displayed jitter at that setting).

Fortunately it's "minor" in the sense that it does not seem to affect intelligibility and is not splattering onto anyone else in the crowded 40m band. If anything I'm using less bandwidth!
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Steve - K4HX
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« Reply #104 on: February 15, 2015, 11:44:06 AM »

 Grin Yea, hyperbole used to illustrate. I think the "mode" is not giving a damn what sort of signal is put on the air. That's a mode I cannot endorse.

Clearly, you learned that there was FM/PM going on in your rig from the dreaded SDR report. OH NOZ! Was the fact that your ARC-5 had FM/PM the end of the world? Not really. Was it useful that someone used their SDR (OH NOZ!) to give you a report? Yes.

Not all signal reports are equal, but they should not be universally ignored. That's just plain stupid.

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WB3JOK
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« Reply #105 on: February 15, 2015, 02:15:56 PM »

A less than successful morning...  heard KC9QJE just signing off, then W9BHI(?) calling CQ on 7295. I came back to him, he got my call, then disappeared! I called him again and got a testy "This frequency is in use" from somebody... Oh well. Shortly thereafter the added rx gain control pot arced audibly and the rx went dead.  Shocked

I suspect that the pot's carbon track failed from electrolytic bypass caps charging up (to a measured 122V), with the cathodes disconnected via the muting relay I'd added. When the PTT is released, it dumps that charge through the pot, which is usually close to the end of rotation... it may be too much current on a small area of the track, not just the surge, but it'd been working fine until I actually started keying the relay. I think I'll replace the pot, and just use the relay to short the secondary of the audio transformer instead! There is a neon bulb at the input to the RF stage for overload protection anyhow...

Anyway I got to work on my 3-4 Mc. transmitter (BC-696A). I desoldered and removed the original connector on the rear (to which I'd previously soldered external wires), and replaced it with an Amphenol octal plug after carefully enlarging the hole slightly with a rat-tail file. The plug wiring is of course identical to my 7-9.1 Mc unit so they can be interchanged easily.

I hadn't had good results with this transmitter when I hooked it up ten years earlier, having taken the "Conversion Manual" shortcut of connecting the output of the roller inductor directly to an SO-239, then to a 50 ohm load. Now that I'm more familiar with the design of the ARC-5, and also screen modulators, I can see why that is the wrong way to connect one! (Recall that they are designed for a very short antenna that appears capacitive and only about 5-12 ohms impedance. Not at all the load that our typical dipole presents). On the scope, although there is decent carrier and a warm dummy load, there was no upward modulation at all at any setting of the inductor and coupling. Largest carrier at no inductor and 100% variometer.

I tacked in a small air variable set to about 68 pf between the inductor and the output (68 pf Russian surplus small doorknob cap on the way). Now, just as with the 40m tx, there is decent upward modulation once the roller inductor is set to about 60% tuning out the reactance, but even with the variometer at 100% coupling, the loading is still insufficient for good 2:1 (100% mod) or better peaks. Looks like this one will need two turns added to the output link - the 40m tx needed one additional turn.

That's enough fun for one morning. No contact, accidentally PO'ed someone, receiver blew up. Typical day in the shack  Roll Eyes
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WD5JKO
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« Reply #106 on: February 15, 2015, 02:33:58 PM »


Charles,

   Sounds like a fine day. Maybe you will feel better if I told you my 8877 based amplifier croaked today. I drive the filament and cathode with RF equally through a trifiliar RF choke, but one side of the filament transformer is still grounded. Looks like I got a hard filament to cathode short. The amplifier keys at 300 watts carrier (was 200w before with an 8V zener in series with the cathode), and then when unkeyed the cathode current stays pretty high. A heater-cathode short will bypass the 50K cathode bias resistor when unkeyed, and will bypass the 8 volt zener when keyed..

   As far as your ARC-5 with incidental PM causing dissimilar amplitude sidebands, you are in good company. A high percentage of prized BA transmitters such as the EFJ Ranger also do this. The issue is the VFO runs at 40m when the transmitter is on 40M. My Gonset G-76 on 15m does this so well that there is a 30 db difference between sidebands. Switch to a crystal and they are equal.

   W8JI touches on some of this with the Valiant:

http://www.w8ji.com/johnson_vfo_chirp_jump.htm

Jim
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WB3JOK
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« Reply #107 on: February 15, 2015, 04:43:51 PM »

Thanks for the link. Might be interesting to try pulling the 1626 and injecting a signal from a crystal osc... don't have a 7295 handy though - and then how do I know if the sidebands are equal anyway Wink

I've been outside cutting up the remains of a tree I had taken down 3 years ago, because I'm getting low on firewood just in time for a significant (for southern MO) snowfall and temps in the single digits (also low for here). Some of the pieces must weigh 4-500 lbs. I'm getting too old and fat for this lumberjack stuff! Maybe fun in the shack is a better way to spend my time.

Ouch on the 8877. I hope you can rewire your filament and cathode circuitry so you don't have to buy a new vacuum bottle...
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VE3AJM
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« Reply #108 on: February 15, 2015, 05:18:20 PM »

Grin Yea, hyperbole used to illustrate. I think the "mode" is not giving a damn what sort of signal is put on the air. That's a mode I cannot endorse.

Clearly, you learned that there was FM/PM going on in your rig from the dreaded SDR report. OH NOZ! Was the fact that your ARC-5 had FM/PM the end of the world? Not really. Was it useful that someone used their SDR (OH NOZ!) to give you a report? Yes.

Not all signal reports are equal, but they should not be universally ignored. That's just plain stupid.



Amazingly today there was a Scripture commentary that rang a bell on this subject from Psalm 135:16,17 regarding "eyes but they do not see, ears but they do not hear" etc. Being subjected to this mind set and attitude over and over on the air, made me think I was in some bizzaro universe where left was right, up was down 5% modulation was good and usable etc etc. Grin

Don't be an "expert" or a contrarian.

Al VE3AJM
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WB3JOK
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« Reply #109 on: February 15, 2015, 10:26:20 PM »

It'll be a few days (probably more, with the snow/ice everywhere) before I can get a new pot for the receiver. Fortunately only one end was burned, so I just turned it around temporarily, and the gain control knob works "backwards" for now.
Also rewired the PTT relay inside the rx to leave the gain control line connected to the pot, and instead disconnects the audio from the front panel jack and shunts it to a 1K 1 watt resistor to ground instead.

Meanwhile I added two turns of Teflon-insulated wire to the 80m transmitter's tank coil in series with the variometer. Naturally I guessed wrong in the direction of the turns (with one turn on the 40m tx it didn't matter) and had to redo it. Why is a 50/50 chance wrong 90% of the time?  Roll Eyes
Edit: Now that I think about it, actually it does matter even with one turn, I must have guessed right the first time.

Anyhow, now the 80m tx also has a nice 2:1 carrier/PEP (or better), although the screen bias pot needed to be readjusted for a different pair of 1625's. At the setting for the 40m tx, the 80m won't go below about 20% carrier.
Nothing on 40m except broadcasters and what sounds like some kind of contest (is the K1N DXpedition still on the air?)

Now I'd like to have a 3-6 Mc. receiver to go with it, but may have to wait a long time for a bargain like the 40m rx/tx I found at the flea market here. The only one on the auction place has a starting bid of $25, missing all the tubes, dynamotor and both covers, has lots of "hammy" wiring hanging out underneath, and he wants $20 to ship it 500 miles. I don't think so.  Tongue May just have to drag my Hallicrafters SX-110 out from under the bench!

Edit: there's another 3-6 Mc. rx starting at $49 and $20 shipping, and it looks like it was run over by a deuce and a half... also there's a new listing for the low-freq (190-550 KHz) buy-it-now for $26 plus $19.90 shipping, looks complete except for the top cover. If you want to make a "Q-5er" this might be worth buying, since it has a very sharp 85 KHz IF.
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Opcom
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« Reply #110 on: February 16, 2015, 11:06:19 AM »

I ran a six cyl dragster for many years too.

6=8
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« Reply #111 on: February 16, 2015, 01:20:10 PM »



there should be one of these with "KEEP CALM" and "ALL IS WELL" over the figures. maybe with flames in the background.
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WB3JOK
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« Reply #112 on: February 16, 2015, 09:20:55 PM »

Somebody bought the 190-550 Kc receiver within hours. $26 even with $20 for postage is not bad for one of those in decent shape. Oh well.

Anyhow there was a good roundtable going on 7295 this evening, which I joined while making some RG-58 cables (attaching PL-259's is something I haven't done in a long time, but it came back to me quickly... and I didn't leave any outer shells off before soldering)  Cheesy

Just wondering, is there much AM on 80/75m these days, or is it mostly 7160 and 7295? Not many posts on the 80m activity board here.

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w1vtp
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« Reply #113 on: February 16, 2015, 09:52:27 PM »

That is also what Tim 'QJE said... he saw the spectrum of another ARC-5 (couldn't recall whose, though) that was also missing most of the lower sideband. It would still takes a lot of incidental FM (or PM) to suppress it near-completely though. Maybe they do "all do that"!  Roll Eyes

<snip>

Just consider it part of the charm of a  classic - - or a challenge to "fix" it.   Grin

Al
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N2DTS
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« Reply #114 on: February 16, 2015, 10:51:38 PM »

Lots of AM on 80 meters in the mornings and mostly at night, starting around 5 pm till whenever, 3870 to 3885 and some lower down in the extra section.
What equipment do you have?
No general coverage receiver?
If you have a computer, you can download the sdr-radio software and use an on line receiver.


Somebody bought the 190-550 Kc receiver within hours. $26 even with $20 for postage is not bad for one of those in decent shape. Oh well.

Anyhow there was a good roundtable going on 7295 this evening, which I joined while making some RG-58 cables (attaching PL-259's is something I haven't done in a long time, but it came back to me quickly... and I didn't leave any outer shells off before soldering)  Cheesy

Just wondering, is there much AM on 80/75m these days, or is it mostly 7160 and 7295? Not many posts on the 80m activity board here.

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WB3JOK
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« Reply #115 on: February 17, 2015, 12:08:21 AM »

For AM I also have the BC-696A 3-4 Mc. transmitter which is now wired up to match the 40m unit (with an Amphenol male plug in the back) so I can swap it in a matter of seconds. The amplifier will work on 80m also. I did mention in passing that I have a Hallicrafters SX-110 so could use that for reception. And my Heath SB-102 transceiver but I'd be twiddling the knob constantly, trying to zero-beat everyone's carrier...

Problem with 80m is the range is so short in daylight, and too many hold-the-frequency-but-never-talk types in the evenings. Will see if the SX-110 is working and can take a listen tomorrow on 80.
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N2DTS
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« Reply #116 on: February 17, 2015, 08:48:36 AM »

80 meters at night takes some power most times.
Around here, there are the usual suspects on 3873, and some groups on 3880 and 3885 out west or down south, they get taken out mostly by the 20+KHz wide class E guys on 3873.

Daytime 80 is mostly very local, at 5pm you can have a nice qso before the zoo starts sometimes.
40 is often good all day and night as long as the broadcast is not on.
That comes and goes, some stations only transmit an hour or two.

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WB3JOK
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« Reply #117 on: February 17, 2015, 04:33:07 PM »

Hmm... I may stick to 40m then (besides, I am waiting for a reasonably priced 3-6 Mc. ARC-5 receiver to use with the transmitter).

On 7160 just now I heard a VERY loud signal from W5WN in Plano TX talking to W0ERE who I could copy only some of the time. QRZ says he's (too) close to me in MO and he said he's only running 13W carrier. Fading is particularly bad today on 40, too. Of course the guy I could hear was just signing off...

Anyhow I was considering building a 3" modulation monitor scope directly into the mostly blank lower rack panel of the amp. I have a 3" CRT, bezel and neck shield, and a HV board with some caps, high-value divider resistors and socket/harness from an old Tek scope with the same CRT base. Don't even need a vertical amplifier, and a simple sweep generator is trivial. The hardest part may be cutting a neat 3-1/8" hole in the 1/4" thick aluminum rack panel...
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VE3LYX
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« Reply #118 on: February 17, 2015, 05:08:25 PM »

For  opcom 6 does =8. slant six against 427 Hilborn injected and racing heads up.(I crashed on this run , broke my spine.)
No 19 wireless next. 8 watts of AM
Anytime you wish to try I will listen. Early morning here and early evenings is best for 80M. Just give me a heads up and a freq
don


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Don VE3LYX<br />Eng, DE & petite Francais
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« Reply #119 on: February 17, 2015, 07:39:09 PM »

Any reason you do not use the sx110?
Or get a viking 2 or something?
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WB3JOK
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« Reply #120 on: February 17, 2015, 08:33:27 PM »

I did start this project with the aim of using ARC-5's, which has been a reasonable success on 40m. Of course, I could use other equipment to get on AM be it 40 or 80 meters...

But there is definitely no room in the shack for more equipment (and anyway there are few hamfests within a reasonable drive of BFE, Missouri).  Cool

I remembered that I had a Tek RM561A (rackmount) scope just gathering dust in the other room, so I pulled it out, dusted it off and mounted it in the rack underneath the amp. It's only good to 15 MHz but that's fine for 80 and 40!

With a small cable running from the vertical plug-in to a simple divider tapped to the amp's output, now I've got modulation monitoring in real time. And the added advantage of having a scope right there at the rig, should I need to measure anything else.

Unfortunately the scope's muffin fan is extremely noisy. It sounds like a vacuum cleaner, or a prop plane running up its engine in the room, and dwarfs the (new) fan I use to cool the 4-125A's. They are fairly cheap, and it's on the back of the scope so I won't have to disassemble anything to get to it. I may even have another quiet fan in the parts bin.
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VE3LYX
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« Reply #121 on: February 17, 2015, 09:48:22 PM »

I picked up a BC454 at a hamfest. The guy gave it to me and I use it with the 80M rig. It was badly beat up but electrically perfect. You could do a crystal converter and tuned front end in front of you 40M rx which would be easy . I use a monitor scope , 2 inch tube I built from an old ARRL book although I only hook it up when necessary. Uses a 220 volt AC transformer for sweep.
 I have seen BC 454s on ebay recently even. Anyway sounds like you have it all in hand.
don
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Don VE3LYX<br />Eng, DE & petite Francais
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