Bakit nasisira ang VHF radio kapag nag-transmit ka ng walang antenna?

[iCapacitor]

Bakit nasisira ang VHF radio kapag nag-transmit ka o kaya naman pinindot mo yung PTT switch ng walang antenna?

[RiDdLeR???]

Yung transmitted power kasi is reflected back to the rf power amplifier and malaki ang possibility na ma-overload or masunog yung components sa power amp stage.

[Born2BeWired]

Agree. Wala kasing magaabsord sa nilalabas mong RF, so everything will be reflected back to the last RF stage. Under this condition, Vce voltage will rise above the maximum the RF transistor can handle, kaya psst! pop! booom!

[Ikasamoko]

Bakit nasisira ang VHF radio kapag nag-transmit ka o kaya naman pinindot mo yung PTT switch ng walang antenna?

But don't worry...pwede mo pindutin..hehehe...di naman agad2 na masisira like press..boom!!

[toasted siopao]

Bakit nasisira ang VHF radio kapag nag-transmit ka o kaya naman pinindot mo yung PTT switch ng walang antenna?

Sure ba na nasisira talaga? Kasi yung sa akin mukhang napipindot ko minsan hehehehe.

[razalas]

Ndi kasi properly terminated, so transmitted power reflect back to transmitting source which lead to overload.

[Ikasamoko]

Sure ba na nasisira talaga? Kasi yung sa akin mukhang napipindot ko minsan hehehehe.

Wehehehe...akala ko ako lang gumawa nyan...hehehe...

pero minsan na noticed ko if nakahiga ako at nag momodulate at wala akong shirt nakapatong yung radio sa dibdib ko then yung battery/charging terminal (IC-02N) lumapat sa skin ko...napaso ako!! cguro ito yung tinatawag na RF burn...

[jctupazvi]

Yun kase ang concept ng VSWR. Because infinite and resistance ng load mo lahat ng transmitted power goes back the the RF PA instead of converting that energy to RF it only becomes heat na makakasira dun sa PA.

[tataflorante]

Mga sir..it so happen na nagwowork ako sa Int'l AM station ...i.e. shortwave transmitter  with a forward power of 100kw,and 250 KW medium wave transmitter and madaming beses ko nang na encounter ang rf burn in which talagang nakakasugat ng skin..transmitting with this kind of power would produce  rf energy which is sufficient to illuminate 40 watts flourescent bulb in line w/ the transmission line..( coz ito ang ginawa naming indicator sa antenna side)whoppps wala nian sa NTC/KBP manual...
but then again, back to the topic, no antenna for any transmitting equipment is a no-no, especially kung walang feedback protection against high VSWR/reflected power..
but if u want to try...then go ahead!

[Ikasamoko]

100kw/250kw...waaaaaaa....that's a lot of wallop!!

sakin nga haggang 5kw lang na fm yung guy wire namin may spark na pag scratch ko using metal...yung 250kw pa kaya?

[tataflorante]

yeah..and Im very fortunate na buhay pa naman..
Ang nickname nung 250 KW Tx is "Dragon" co'z para talagang dragon kung may arcing sa combiner
but anyway due to all power tubes ang operation, shut down na po ang 250KW AM, very memorable po yan para sa kin coz ngayun lang ako nakakita ng transmitter na kapag i- on mo ang HV( High Voltage), kaya niang i brown-out buong barangay...nyahhhh..

[Ikasamoko]

Sa mga xmitter din ako nakakakita ng mga resistors  na kasing haba ng mga fluorescent tube...

[tataflorante]

yes Sir madami dito nian, 2 klase yan..1 resistive and 1 Inductive, usually gamit yan sa bleeder ckt, or acting as a coil. Minimum wattage usually sa PA section is 100 watts resistive.

[Woots29]

ginagawa ko rin minsan ung sandaling press kahit walang antenna

taga-ayus kasi ako ng baterry pack

[bravokilo]

Hi! we all learned a few things during the CB days and the 2Meter days. Yes RF shock is real. May humawag dun sa car antenna ng VHF TX putting out 45 watts. wham...RF is real energy. Gamit noon neon bulb to sense RF. Ewan ko lang kung sisindi yung nasa screwdriver pang testing AC. Alisin ciguru yung resistor sa loob. I kept schematics but I do not know where they are.  I have a book on CB, yung luma na 21 channels pa at maraming crystals. I also have the Motorola handbooks.

     On the buring of the finals when we transmit without an antenna, we noted that the UFH Icom on 430 Megs was in fact more prone to burning.  That is probably one reason the FRS radios on 430Megs have fixed antennas.

     I built several transmitters for RC (max 1 watt) and noted that the final Q is highly reversed biased with a 470 ohm resistor.  Other than setting the region in which he final Q should operate,from a practical perspective, protection yung dun sa Q para hindi mag "runaway".

     The final Q is driven by a driver Q either via a capacitor or via a transformer.  The final Q is made to oscillate at the driven frequency but at a higher amplitude (higher current). The high f energy is made to run through the coax to an antenna. We can imagine the signal as nag cha cha cha dun sa antenna. Urong sulong.  Kung ang run niya perfect fun sa length ng element, yun mag vivibrate yung antenna sa optimum level and will radiate the energy into free space. kapag hindi tuned and antenna, some energy will return to the final Q. Ito nga  ang VSWR, comparing the forward signal to the reversed signal.  Usually up to 1.5 and acceptable. Now pag WALANG ANTENNA..... hmmmmm. The energy run through the coax and does not find a "load" sa dulo. Remember sa audio amp, we face the same risk. Pag walang speaker sa dulo, walang load, baka masunog and amp section.  mas lalo na kapag walang coax pati. Oopssss. Hinde na reflected power kasi di nga nakalabas. Kulob power na.  Yung final transistor keeps oscillating at high F and high current na walang labasan. Mag runaway siya, thermal runaway. Ayun, pssttt.....Ala ng signal.

Ang SWR ay importante and we can make one. Sa ARRL. Pwede magburn and finals kahit may antenna na masyado mataas and SWR (Standing Wave Ratio).  Yung pang 250 kwatts. Aruy, ang lakas ang energy nakakulob.

BK

 

[Ikasamoko]

Hi BK...baka meron ka mga pic dyan pag opera ng PA ng mga ICOM like 02A/N...

[bravokilo]

Hi Kas, what's PA? power amp? yung finals? May kumpleto akong schemas but I can't find them., Mag inventario nga ako.  I have a bout a dozen 2 meters...mayrun pa nga ako dati yung pictorial paano buksan pero nawala na.

BK

[Ikasamoko]

Yep power amp ng mga 02N/A....yung goldfinger ang napuputol dun...kaya lang ijumper...

[thesaint119]

parang audio amplifier din yan kailangan ng resistive load kaya lang at very high frequencies, saka yung audio sa sound, yung transmitter sa rf. kapag wala kang antenna as load sa radyo yung buong rf votage na lalabas sa transmitter mo babalik sa kanya ng buong buo, yan yung reflected output...sisrain nyan ang mga output transistor mo kasi dun lahat babalik ang output non..

[Nobita]

yeah..and Im very fortunate na buhay pa naman..
Ang nickname nung 250 KW Tx is "Dragon" co'z para talagang dragon kung may arcing sa combiner
but anyway due to all power tubes ang operation, shut down na po ang 250KW AM, very memorable po yan para sa kin coz ngayun lang ako nakakita ng transmitter na kapag i- on mo ang HV( High Voltage), kaya niang i brown-out buong barangay...nyahhhh..

Gaano naman kalaki yang "Dragon" hehe