[ARC5] T-19 first run issues.

Mon Apr 20 23:11:33 EDT 2020

Perhaps the hum is due to an overloading issue in your receiver?  Are you able to look at the RF waveform using an o-scope, or just using a local receiver?  You might try putting a signal out on the air and listening to the signal on a Web SDR that is capable of receiving it.  I routinely monitor my transmitters modulation waveforms using an o-scope that has enough bandwidth to look at RF signals (currently a TEK 422, rated at 20 MHz, but usable qualitatively out to 30 or more).    I sample the RF using about ten turns of a clip lead wire wrapped around the coax antenna feed line into the scope vertical input with at least an RF choke bridged across the input, or a parallel tuned resonant circuit, often use an old National MB-40 transmitter tunable coupling network.  If you have multiple antennas available, you could use one not connected to the transmitter to feed into the oscope.  The 422 has enough sensitivity to display the waveform of the local broadcast station on 1230 kHz about two miles away when using a tuned input circuit and an external antenna.  Also the transmitted waveforms from my neighbor, Joe,  N1VIV about 1000 feet down the street!  Even a random wire around the shack loosely coupled to the transmitter under test into a scope vertical input should work.  Be sure to have some sort of tuned circuit or at least the aforementioned RF choke across the input, otherwise all you will see is a 60 Hz sine wave, even with the transmitter off! (The equivalent of putting your thumb on the tip of an audio cable connector going to the input of an audio  amplifier.)

Chris, AJ1G Stonington CT

Sent from my iPhone

> On Apr 20, 2020, at 19:40, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> 
> It is ground related after all, but not so much the boxes, but needing an EARTH ground.
> I just have all of this sitting here  a dummy load. I found that if I connect the frame to my earth ground the hum diminishes to almost nothing . Must be modulating against the open AC ground ? 
> 
> On Monday, April 20, 2020, 7:00:18 PM EDT, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> 
> The installation is on a metal framework. The prior inhabitant, an SCR274, was connected to the shelf and frame better than the ARC5 is at present, But I make use of the ground clips on the rack. I used some clip leads to connect  the boxes as test to see if that helped. Unfortunately, it didn't.
> I pulled the MD7 oscillator tube as well, no joy on that either. 
> The carrier hum sounds just like a 120 cycle hum from an AC supply .
> The power supply I'm using is an old industrial SMPS , so no 120 Hz from that!
> 
> On Monday, April 20, 2020, 5:46:52 PM EDT, Michael Hanz <aaf-radio-1 at aafradio.org> wrote:
> 
> 
> Amen.  It's one of the reasons I use aluminum liberally for the support racks in my rig.  Reproduce the environment that they had in the aircraft, and you'll head off a lot of strange problems you sometimes get with grounding/bonding/shielding inadequacies.
> 
> https://aafradio.org/flightdeck/layout.htm has some construction thoughts on the bottom half of the page.
> 
> - Mike  KC4TOS
> 
> On 4/20/2020 12:22 PM, Mark K3MSB wrote:
> 
> Ground all your "boxes" together directly;  don't rely on the connectors.   
> 
> Mark K3MSB
> 
> On Sun, Apr 19, 2020 at 1:26 PM J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> Just got this ARC-5 system wired up and going. Even the rack had hacked/dry wires that needed rewiring.
> The T-19 was recapped, cleaned, etc.  
> 
> I have this strange problem with a hum in the carrier.  It sounds like a rig with a bad filter cap. I rechecked my wiring, etc, but everything is OK.
> The only other "symptom" is low output, about 2  Amps in CW mode . ( It's not the meter because I use the the same one with the SCR274 which will go 3+ amps). I'm using an A-27 dummy load
> 
> I'm thinking that it may be an alignment issue where the finals are off-resonance and drawing too much current compared to the carrier amplitude and inducing a ripple modulation? 
> It's real subtle when looking at it on a scope, but obvious on a radio.
> The Dynamotor is almost ripple free , putting out around 590V under load. 
> 
> Any thoughts?
> 
> 
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