Hi Ron. I did notice that my Philco 41-255 with its loop antenna does not have a static problem at all. I'm half way thinking about putting a similar loop antenna in the Sky Rover just to see what effect that has. I also thought about using my landline as an antenna but that line is still active. Yes, I still use my landline!! However, all the utilities in my neighborhood are underground so I'm not sure how effective it would be as an antenna.
Rich
Hi Everyone! First, I wanted to thank all for your kind comments and encouragement. The radio is still up and running. I just had to try a sort of 'proof of concept'. I made a loop antenna with 2 turns of number 12 copper wire. I put one end in a vise and the other end in my drill and ran the drill for 20 seconds or so. That straightened and hardened the wire. I spaced the turns about 3/4" apart and put the assembly in the back of the radio as shown in the picture below. Ya'll can't give me a hard time about the 'sloppy proof of concept', just say'n!! I wanted to see if that antenna would attenuate some of the static on the high end of the AM band. The results: reception doesn't seem to be negatively affected, and the static is greatly attenuated. I'm able to receive some of the weaker stations. So, I'm thinking of trying to come up with a more permanent and better looking solution. I may very well have to tweak the antenna padders, might be worth looking into.
Thanks again everyone!!
Rich
Long wire antennas can bring the static and interference. I have for experiments attached the radio to my home radiator and use the steam pipe system for an antenna, the gain is very strong but it also can amplify interference. Sets with a loop can often be paired with an inductive loop with and null most of the static. Good luck good listening, Paul.
Sloppy proof of concept??? That is rather clean IMHO, great job.
I think that most RF sections of tuning caps are 10-365 uF. Hooking a loop antenna directly to the antenna and ground terminals will yield a low signal. Try a Ferrite loop antenna meant for broadcast band, preferably for a tube type radio and install it in lieu of the antenna coil. Remove the secondary of the antenna coil, usually connected to the "RF section" of the tuning cap and the AVC line and replace it with the loopstick. However, this may be tricky if the set is Broadcast / Shortwave.
There are 3 advantages to ferrite loopsticks:
They are directional, like any loop antenna. Turning the loopstick or the entire radio in a direction that
maximizes signal and minimizes interference can make a big difference in signal quality over even a goodoutdoor antenna.
Ferrite loopsticks have an advantage over loop coil type antennas for certain types of interference.
Ferrite loopsticks are more compact than loop antennas. This may allow for more inconspicuous
installation and may allow for rotating the loopstick instead of the whole radio, important for desiredplacement of the radio for room decor reasons
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
RichG that antenna looks great. The thing I wonder about is impedance matching. That loop is low impedance whereas a long wire is high so I would think you would need some kind of matching transformer for optimal signal strength. It seems to be working for you though, I just might give that a try too!
I'm under the impression that the low impedance is the main reason for the low noise. It's harder for noise to generate an antenna signal into low impedance. I looked at a loop antenna once which had the higher-turns coil as the primary. The radio station signal had to overcome the lower impedance of the secondary but noise was not capable.
I was also concerned about impedance matching, but I'm not quite sure how to go about it. I do want to tweak the antenna padders to see if that makes a difference. But I have to take the chassis out of the cabinet to get at the padders. I'm thinking removing the chassis and loop antenna will change how the loop interacts with the radio.
When it comes to using a ferrite loop antenna, I'm afraid I'm out of my depth on that one. I'm not sure what loop would be appropriate and not sure how to implement it. Would a broadcast ferrite loop work on medium and short wave bands?
Rich
On my 41-250 I am surprised how well the shortwave bands work with the loop antenna but then the radio was designed for it. Any impedance matching is designed into the front end already. There is a 3 terminal Jack on the back of the chassis where you can plug in a special Philco adapter that allows you to connect a long wire antenna supposedly for better SW reception. I don’t have that adapter so can’t report on its effectiveness. I am working on a 39-25 which is a long wire antenna set. When it’s done I might play around with making a homemade loop for it.
Hi Ron, I found that my 41-255 does perform fairly well on the shortwave bands. But, like you said, the impedance matching is already built in. I did try another antenna option, the radio wants a long wire antenna so I made another one out of CAT5 cable. I cut off about an 8 foot length of cable and wired the twisted pairs in series with one another. So I ended up with 32 feet of antenna that is folded on itself. It is end fed, the other end is not grounded. It works rather well, and, unfortunately, so does the static. I coiled the cable into a loose coil and that made a reduction in the static. But it also made a big difference in SW reception. Whereas my loop did not do very well on SW reception. I still think the antenna padders need to be checked with the loop attached. Probably grasping at straws!!
Let me know how your homemade loop works on your 39-25.
Rich
Well, here is an update of my proof-of-concept loop antenna. In order to try and match the loop impedance to the radio, I inserted two 1mH chokes in series with the antenna connections. One choke to the antenna connection and one choke to the ground connection. Impedance matching would be ideal, but this was more of a case of trying to increase the loop impedance. I do notice an increase is signal strength, unfortunately there is also in increase in the static but it's not outrageous. It is extremely unusual for me to get Fort Collins, Colorado on 10MHz in the daytime. But WWV comes in quite strong, and it's nice to know the clock on my wall is only 15 seconds fast!! Just as another 'what if' test, I shorted out the choke that went to ground and I lost WWV immediately. On the AM band, shorting out the choke to ground reduces the signal strength by quite a bit. I tried adding a third choke in series with the antenna connection but didn't really notice any major changes. I'm thinking the two 1mH chokes may be the best I can do for the time being. I think this is a case of increasing the loop impedance by a fixed amount being okay on one band but not the other bands. I may play around with adding a capacitor to the mix to see if that makes a difference. If anyone has suggestions, I'd like to hear them. As you can probably guess, my antenna skills are a bit lacking!
Thanks everyone!
Rich
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