A question regarding the extendable antennas

[prcguy]

What? I have an 80m AM HT with 3ft telescoping whip and it works just fine, got about 27mi range on it once. Anyway, a long extendable tuned antenna on a hand held scanner will hear things a stock rubber duck or 1/4 wave whip can't. Its a nice upgrade if your stuck with a hand held and no outside antenna. It will only be good on one band and for a limited range of frequencies, but for someone that concentrates on the railroad freqs like the OP is doing, its perfect.

"You can get the same thing for the RR band, a tuned resonant 1/2 wave or 5/8 wave extendable whip for a hand held scanner that will bring in stuff you can't get with an RH77 or anything similar."

Yes. With a couple'a qualifications. An HT (or scanner) is only for convenience. It isn't ever going to be the 'best' way of doing any kind of communicating unless you are talking about -short- distances. The biggest problem is the antenna. Can't get it very 'efficient' unless you make it more inconvenient (longer). With VHF/UHF that inconvenience is 'do-able'. For lower bands it's not so 'do-able', ain't gonna use no 80 meter HT! I can yell louder than that. (Yeah, I know, but it illustrates the point.)

 

[W5lz]

What? I have an 80m AM HT with 3ft telescoping whip and it works just fine, got about 27mi range on it once. Anyway, a long extendable tuned antenna on a hand held scanner will hear things a stock rubber duck or 1/4 wave whip can't. Its a nice upgrade if your stuck with a hand held and no outside antenna. It will only be good on one band and for a limited range of frequencies, but for someone that concentrates on the railroad freqs like the OP is doing, its perfect.

Then you have a very unusual HT if it 'talks' on 80 meters. I have to assume that HT has a QRP power level, and if so, 27 miles is exceptional even if it was only once.

 

[prcguy]

Its a WWII BC-611F on 3.885MHz AM and its not unusual, lots of them are fired up every year at the Dayton Hamster fest. The output power is between 1/2W and 1W. In the 27mi case I talked from my back yard to a WWII ship (Lane Victory) on a test run around Catalina Island off the coast of So Cal.

Then you have a very unusual HT if it 'talks' on 80 meters. I have to assume that HT has a QRP power level, and if so, 27 miles is exceptional even if it was only once.

 

[W5lz]

Then I'd have to say a BC-611F is unusual...

 

[prcguy]

I think there are more BC-611s out there than Smiley brand 1/2 wave telescoping HT antennas.

Then I'd have to say a BC-611F is unusual...

 

[cbehr91]

I have an MFJ-1714, which is advertised as a end-fed 1/2 wave for 2m. It extends to 40", but I don't extend the very top section for VHF-Hi monitoring. In just listening test it works really well, and I would have to think it would hear better than a 1/4 wave helical, whip, or rubber duck using the radio case as the other half.

 

[W5lz]

That half wave antenna also uses the case (and you) as part of the complete antenna system. If it were center fed it could be thought of as not using the case etc, but it's not center fed.

 

[prcguy]

Not so much, a half wave end fed doesn't need a counterpoise and there is matching stuff in the base of the antenna. In testing on a very small antenna analyzer there is no difference in the match with the analyzer and antenna sitting on a table vs holding it in my hands. Most other antennas will change drastically when doing this but not the 1/2 wave types.

That half wave antenna also uses the case (and you) as part of the complete antenna system. If it were center fed it could be thought of as not using the case etc, but it's not center fed.

 

[W5lz]

Two terminals are required for current to flow. With an antenna, the vertical part is one of those terminals. The 'other one' is typically the case of the handheld radio and by extension, the user's hand/body. With a center fed antenna the two 'terminals' are the two 'sides' of that antenna. Same with a vertical antenna, the 'other' terminal is 'ground' or counterpoise, right? With an HT the same thing has to happen. The difference is in where/how that 'other half' is furnished. With an HT that 'how/where' is a combination of the HT's case/circuit board, and typically, the user's hand/body. It doesn't matter what 'size' the antenna is, it still has to have those two terminals, so, where is it?
That coil at the base of the antenna is for impedance matching and enough inductance to make the antenna seem longer. Those coils are very commonly tapped with that tap going to 'ground'.... there's the 'other half' of the antenna, the 'ground/counterpoise'.

 

[prcguy]

Yes and no. Look at most half wave antennas like a J-pole, EFHW wire, Cushcraft Ringo, etc. There is current flowing in the primary of a matching transformer which satisfies RF current flow back to the source but then couples to the single half wave radiator, who's impedance has been matched so current will flow into it. That half wave radiator is being excited and radiating all or most of the energy and the other half of that circuit is radiation resistance. When the RF is carried away via electromagnetic radiation, you complete the circuit.

Or look at the real Windom antenna with a single feeder wire up to an offset center fed radiator. There is only one wire going to a resonant half wave radiating element from the antenna tuner. There is a ground connection at the tuner but that could be 50ft away and has little influence on the antenna above. The single wire feeder doesn't radiate. Why? Because its delivering RF current to the resonant half wavelength of wire which has radiation resistance and it might as well be a load resistor fed with coax or balanced wire. It works and its magic, just leave it at that if you don't understand it.

Two terminals are required for current to flow. With an antenna, the vertical part is one of those terminals. The 'other one' is typically the case of the handheld radio and by extension, the user's hand/body. With a center fed antenna the two 'terminals' are the two 'sides' of that antenna. Same with a vertical antenna, the 'other' terminal is 'ground' or counterpoise, right? With an HT the same thing has to happen. The difference is in where/how that 'other half' is furnished. With an HT that 'how/where' is a combination of the HT's case/circuit board, and typically, the user's hand/body. It doesn't matter what 'size' the antenna is, it still has to have those two terminals, so, where is it?
That coil at the base of the antenna is for impedance matching and enough inductance to make the antenna seem longer. Those coils are very commonly tapped with that tap going to 'ground'.... there's the 'other half' of the antenna, the 'ground/counterpoise'.

 

[W5lz]

But i do understand. That Windom antenna is correct in as far as you described it, but you didn't finish. A Windom antenna is always 'worked' against ground. If you don't have a good RF ground system under that Windom, it isn't a Windom antenna anymore, just an end fed wire which is depending on there being a ground somewhere else (typically the coax shield ~if~ fed with coax). And I'm sorry, but that single wire feed line ~does~ radiate. Typically, that radiation isn't comparable with the Windom (or horizontal wire) above it, but it does radiate and is a part of the overall radiating mass.