Home |
Search |
Today's Posts |
|
#1
![]() |
|||
|
|||
![]()
Hi,
As a beginner in SWL I hope that somdebaody can give me some advice: I have Yaesu FRG-100 which I want to set up primarily for HF Airband monitoring so I need to install an antenna. From what I have already read a longwire is the solution, but some references refer to connecting the wire directly to the receiver and others talk about a Balun. Since my receiver has two antenna connections (1 hi impedance and 1 low impedance) I assume that if I connect just the wire I connect it to the high impedance but if I use a Balun I can connect to the low impedance. But what If I do not use a Balun and connect to an ATU instead , the output from it is PL259 coax connector do I just connect this to the low impedance input or to the high impedance one. Or do I connect the balun close to the antenna and use a coax feed between it and the ATU low impedance input. To get the required length if I was to run the antenna in my attic is it reasonable to loop it around the attic several times or should it be a single loop. When calculating the required length I assume that full wave is preferable but if its not possible then it should be calculated to be 1/2 or 1/4 is that a correct assumption. Is there any drawback in having it shorter than fullwave ? Should the antenna wire be insulated or non-insulated type ? Any help would be appreciated on the above. regards Birderman |
#2
![]() |
|||
|
|||
![]()
Birderman wrote:
As a beginner in SWL I hope that somdebaody can give me some advice: (welcome!) From what I have already read a longwire is the solution, but some references refer to connecting the wire directly to the receiver and others talk about a Balun. Since my receiver has two antenna connections (1 hi impedance and 1 low impedance) I assume that if I connect just the wire I connect it to the high impedance but if I use a Balun I can connect to the low impedance. But what If I do not use a Balun and connect to an ATU instead , the output from it is PL259 coax connector do I just connect this to the low impedance input or to the high impedance one. Or do I connect the balun close to the antenna and use a coax feed between it and the ATU low impedance input. Both the balun and ATU have (relatively) low-impedance outputs - should be connected through coax to the low-impedance input of the receiver. If you use both, then yes, the balun connects to the ATU's low-impedance input. To get the required length if I was to run the antenna in my attic is it reasonable to loop it around the attic several times or should it be a single loop. Additional loops beyond the first won't make a huge difference but if you already have the wire - and don't have the space to spread it straight out - then it won't hurt to loop it more than once. When calculating the required length I assume that full wave is preferable but if its not possible then it should be calculated to be 1/2 or 1/4 is that a correct assumption. Is there any drawback in having it shorter than fullwave ? For receive applications there is no "required length". The preferable value is "as long as possible". The longer the antenna, the more effective it is. "Magic" lengths like full-wave, 1/2 wave, 1/4 wave are mostly for transmitting applications. These magic lengths have predictable impedances that can be connected to transmitters without risk of overloading high-powered parts. If you don't intend to transmit, then you don't care. "Magic" lengths are also somewhat directional. However, if you have no way of aiming your antenna at the desired stations (it looks like you don't) then there's no point in using an intentionally-directional antenna. In any case, once you place it in an attic (and not outside in the clear) the directional characteristics are unpredictable. Point being, just make the wire as long as possible and don't worry about any specific length. Should the antenna wire be insulated or non-insulated type ? If it isn't going to come in contact with conductive objects (electrical conduits, heating ducts, etc.) then it doesn't matter. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
#3
![]() |
|||
|
|||
![]()
Birderman,
May be I can add to some of "DSs" good points. = = = Doug Smith W9WI = = = wrote in message ... Birderman wrote: As a beginner in SWL I hope that somdebaody can give me some advice: (welcome!) From what I have already read a longwire is the solution, but some references refer to connecting the wire directly to the receiver and others talk about a Balun. Since my receiver has two antenna connections (1 hi impedance and 1 low impedance) I assume that if I connect just the wire I connect it to the high impedance but if I use a Balun I can connect to the low impedance. But what If I do not use a Balun and connect to an ATU instead , the output from it is PL259 coax connector do I just connect this to the low impedance input or to the high impedance one. Or do I connect the balun close to the antenna and use a coax feed between it and the ATU low impedance input. Both the balun and ATU have (relatively) low-impedance outputs - should be connected through coax to the low-impedance input of the receiver. If you use both, then yes, the balun connects to the ATU's low-impedance input. For a 'quick-to-build' SWL Receiving Antenna "Only" a simply and cheap TV 30075 Ohm Matching Transformer with the two twin lead connected to the Loop Antenna Ends. Use good quality DSS type 75 Ohm Coax Cable as the antenna Lead-in to the ATU/Radio. Then use a "F" Connector to PL-259 Plug 'Adapter' to make the ATU/Radio connection. NOTE: This is TV Component type of SWL Antenna is generally good performer above 5MHz and beyond 30Mhz. Plus these TV type 'components' are all available from your local RadioShack/WalMart. To get the required length if I was to run the antenna in my attic is it reasonable to loop it around the attic several times or should it be a single loop. Additional loops beyond the first won't make a huge difference but if you already have the wire - and don't have the space to spread it straight out - then it won't hurt to loop it more than once. If you do use additional Loops, try to get about 12" between each loop winding. Start about a foot above the Attic 'floor' and work your way up in progressively smaller loops for 3-5 windings. (Vice having all your loop winding clumped together in the same space.) This expands your antenna's "Capture Area" and may not add to the signal level but can reduce the monentary variations in signal level (Fading) and that is worth something with weak signals. When calculating the required length I assume that full wave is preferable but if its not possible then it should be calculated to be 1/2 or 1/4 is that a correct assumption. Is there any drawback in having it shorter than fullwave ? For receive applications there is no "required length". The preferable value is "as long as possible". The longer the antenna, the more effective it is. For receive antennas, that are used over the full range of MW & SW Bands there is no one wavelength. Simply as stated Longer is better and with 2-4 extra loops, you will double the length and re-double the length of your antenna. "Magic" lengths like full-wave, 1/2 wave, 1/4 wave are mostly for transmitting applications. These magic lengths have predictable impedances that can be connected to transmitters without risk of overloading high-powered parts. If you don't intend to transmit, then you don't care. "Magic" lengths are also somewhat directional. However, if you have no way of aiming your antenna at the desired stations (it looks like you don't) then there's no point in using an intentionally-directional antenna. In any case, once you place it in an attic (and not outside in the clear) the directional characteristics are unpredictable. Point being, just make the wire as long as possible and don't worry about any specific length. Should the antenna wire be insulated or non-insulated type ? If it isn't going to come in contact with conductive objects (electrical conduits, heating ducts, etc.) then it doesn't matter. Generally for "ATTIC" Antennas: Insulated Stranded Wire between 18-24 AWG is recommended for ease of handling the wire and to reduce potential electrical safety problems. TIP #1: I used Plastic Coated (Metal) Cup-Hooks to install an Attic Loop. Mark off your mounting points and place your cup-hooks. The 'run' your wire and make your connections. TIP #2: A direct Ground Wire to the ATU/Radio will do for this type of attic Loop Antenna. CAUTION: Watch Your Step in the Attic. Also while you are in the Attic, take a look at the electrical equipment and wiring that is up there. If you find any safety and electrical problems in the Attic: Get Them Fixed; or fix them yourself. OBTW: If you do have alot of electrical equipment in your Attic or a Metal Roof: You may wish to re-think puting any Antenna up there. iane ~ RHF .. .. |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Antenna building questions | Antenna | |||
Putting a Ferrite Rod at the Far-End of a Random Wire Antenna ? | Antenna | |||
FS: Connectors, Antennas, Meters, Mounts, etc. | Antenna | |||
FS: Connectors/Adapters/Meters/Etc. | Equipment | |||
Outdoor Antenna and lack of intermod | Scanner |