Many thanks to SWLing Post contributor, Frans Goddijn, who writes:
I bought the Hurricane AM Modulator.
Here in my living room the hum was considerable even though I had an EARTH connection. So what I did was use a coax cable made of two different ends of coax cable, just the isolated kernel of both taped close together so the signal is transmitted on one, received on the other without the wires touching. One end in the antenna OUT of the transmitter, the other end in antenna IN of the receiver.
Now I can wirelessly send music from my laptop or telephone to the Hurricane and ‘receive’ it on the radio of my preference.
The HUM obviously does not originate from the Hurricane.
Click here to view on YouTube.
Click here to check out the Hurricane AM transmitter on eBay.
Thank you for sharing this, Frans. The Hurricane sounds amazing via that gorgeous Hammarlund SP-600!
I found that moving the aerial away from the house helped enormously, and using hum cancellation got rid of the last vestiges of it altogether. My little AM set up sounds superb, using a four chip MW synthesiser (4060, 40103, 4046 and 4013 (to give an equal mark / space ratio) and a PWM modulator using a 4053, followed by a little two transistor linear amplifier. The modulator itself uses a couple of dual op-amps and a THAT4301 audio processing IC to give accurate modulation depth compression and limiting. I’ve been very pleased with the results!
Ken suggested “Maybe running the AM transmitter on batteries would resolve the hum”
Noop… almost always makes no difference whatsover…
(What follows assumes the following… Antenna is inside house, Transmitter Earthed and the Power Supply is good quality)..
1. Transmitters antenna is short (re FCC rules) and is close to house wiring (in an average room you are never more then 6-10ft away from mains wiring…
2. House wiring is an ideal antenna being many hundreads of feet long… (random wire antenna)
3. Unfortunately it also has 50/60hz mains at 115/230v ..
4. result is it re-transmits the signal with the hum…
Solution is to move the transmitter antenna away from house wiring..
One way to do this is to use coax to feed an external antenna whilst keeping the transmitter inside..
Also try antenna in vertical & horizontal position this sometimes helps
Quite often changing the frequency will also reduce or ever get rid of the hum
Its just trial and error…
The last two animations in the video show what happens…
(hope this helps)…
The hum issue is unlikely to be due to the modulator. It’s almost certain to be mixing with the mains 50 / 60 Hz (according to where in the world you are), as described on the 6V6 “help” page.
yes like Tony Williams who produced the modulator wrote:
“Follow this link to see a video on how to stop hum on LPAM transmitter installations.
99% of hum problems are nothing to do with transmitter (any make), it’s almost always induced hum in the house wiring.”
I have a bunch of Joe Frank monologues and old radio shóws from the 1930s thru the 1950s that would keep a AM micro transmitter busy for years
Archive.org has a lot of vintage radio shows you can download free
Superb! I have subscribed to the Joe Frank website’s archive.
I have to wonder if hum would be a problem in a PWM AM modulator like the one used in the Rockwell/Collins Power Rock MW transmitter.
Follow this link to see a video on how to stop hum on LPAM transmitter installations.
99% of hum problems are nothing to do with transmitter (any make), it’s almost always induced hum in the house wiring.
Bye the way I designed the Spitfire, Hurricane and the Tornado.
Maybe running the AM transmitter on batteries would resolve the hum
I also tried a good old “Delta Elektronica” lab power supply which did not make a difference. The “earth’ connection dimmed it a bit but ‘twining’ the coax cables eliminated it so for no I will keep it that way until I feel like experimenting more.
Getting rid of hum on small AM transmitters is one of the “black arts”! There is a lot written about it on the American “Part15.us” website. My little Part 15 transmitter (running around 100mW into a short whip aerial) has a useful range of around ¾ mile, and the trickiest part of setting it up was nulling the hum that was partially induced from the mains. My resoltion for the issue was a “humdinger” – a trick that was frequently used in tape recorders. You introduce some low-level 50 Hz signal in the appropriate phase to null the hum out – if done carefully, it results in a completely clean signal.