Hello all...I have two am radios, and I turn one on a station, then place another am radio behind the first...and the second radio has an external radio connected, so why does the first radio get louder, or pick up better when you tune the second radio to the freq of the first radio...does this make since???


I think they must be tuned together as on and that is why...


Kenny KE4HVE

They are very competitive?

It could be the loopstick of the one radio is boosting the antenna of the other, thus increasing the signal.

I have noticed this when using a Superadio and setting a smaller radio nearby.

In fact, I just did it with my DX-370, which I placed in front of my Superadio 1. I tuned the DX-370 to a distant regional station, which was barely coming in. When I tuned the Superadio to the same frequency (volume on the Superadio down, of course), the signal on the DX-370 boosted by about a DB.

In this case, the 200mm loopstick of the Superadio is acting like a small external MW loop.

Inductive coupling. The antennas are electromagnetically charged, and interact with each other. This is what a Terk Antenna does,although the Terk doesn't have its own power source. Cordless cell phones also charge by induction. When you place two radios near one another and tune one of them 455 khz lower than the other, you hear that hetrodyne squeal,or birdie to test the oscillator circuit. That's through induction.

The first radio is OFF...and that is why I was wondering what was going on..

This would solve the problem where a am radio dont have an external antenna plug..so all you would need it the one plugged into the external antenna and the second one will pick up better..

I guess it would work as an SELECT-A-TENNA Antenna too.


KNY

What radios were you using for this experiment?

The radio that is off is a Channel Master(Sanyo) 6515 and a Channel Master 6528, both are transistor radio's.

The radio that was off (the 6515) has an external antenna jack on it..so that is why I used it...and this radio stays off..

The other one is a 6 transistor radio.

It was just something I was playing around with...


KNY KE4HVE

The second radio is acting similarly to a Select a Tenna, essentially increasing the capture area of the first set. I would expect the bigger the loopstick on the second ( passive ) radio, the larger boost you would experience.
Years ago I built an open wire loop like the old tube radios had in the 1920's. It was about 20 inches square. I tuned it with a salvaged variable capacitor and the signal boost I got from that rig was incredible, just by setting it close to my portable set.

You had a tunable loop. I built one a few years ago, using a 23" wood circular quilting frame. It's performance is equal to the 240' random length long wire antenna I have on my back acre.

It was done before...

viewtopic.php?f=1&t=333651

Yup, those passive loops work gangbusters, surprised how they can beat an external long wire, and they are easy to move so you can null out interference. I will have to build another one some day, just for nostalgia.

Hey Richard---how about some details on your hoop-loop such as type/gauge of wire and how many turns ? Standard 365 pF tuning cap ?

Thanks !

John

"(The second radio is acting similarly to a Select a Tenna, essentially increasing the capture area of the first set. I would expect the bigger the loopstick on the second ( passive ) radio, the larger boost you would experience)"


Bob, would it be the other way around, the first radio, that is turned off, acts as the Select-A-Tenna, and the radio(smaller one) is the one Im listening to...?

I made a tunable antenna too, with a USPS large flat rate box, I wrapped 15 turns around the outside edge, and placed a 365pf tuning cap in an opening I cut out on one side, in the middle of the box, then I ran the wire's to it...one to the ground of the cap, and one to the lugs, and it works pretty good..The tunable part of the tuning cap was pushed thru the middle of the box...and I used the mounting screws from the original mount to hold it there..


KNY

Hey John, I did a thread on it a few years back. The frame was a quilting hoop, coil 60 feet of #24 Celanese covered wire, IIRC, about 16 turns, and a 410 pF BCB tuning cap.

Just for yuks, I hooked up a 1N64 Diode and small Rat Shack amplifier to it, and got about 17 stations one night.

Yes, it would be the radio that is turned off that is acting as a passive antenna for the live radio.

I modified my passive loop by putting a single turn pick up loop and fed that to a FET preamplifier. That way I could use the loop with radios that did not have a loop for the AM band. I fed the output with coax to the receiver, itworked well.

take even the cheapest AM radio and place a Select-A-Tenna about 4-8 inches away from the ferrite stick, perpendicular to it...and listen to what happens...

steve

Hey Richard---do you have a link to that thread ? I thought I remembered seeing your loop before, but wasn't sure where...

Bob S---that's a great idea ! As an experiment, I made a single FET receiver using a loopstick and tuning cap which would pick up a couple locals clearly with just a short length of wire and it had really good sound quality & very low noise---that simple amp would probably work wonders with Richard's hoop !

John

With three radios you can make a poor man's Theremin:
https://www.youtube.com/watch?v=PSYPUhPGavQ

You could use one of the many four or five transistor sets that had a regenerative detector stage, they were very susceptible to hand capacitance effects, which made them hard to tune. Add another radio, or three, and you could have a symphony.