Posted by: DJ Adam Eve
« on: February 19, 2012, 02:00:00 pm »Good luck
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Posted by: DJ Adam Eve
« on: February 19, 2012, 01:58:28 pm »For length of radiator its speed of light divided by frequency, so meters would be 300/87.8 thats multiplied by the velocity factor of free space so x0.935 then multiply that by 5/8 so x0.625
((300/87.8)x0.935)x0.625=1.996 meters.
Because of the length the radiator will end up with capacitive component which you tune out using coil. Given your low frequency I would build the coil to Jans dimensions but with an extra turn/ half turn, then using your swr meter stretch/ compress/ trim the coil to minimum reflected power on the meter. Calculate the radials with same formula but instead of 0.625 multiply by 0.25.
Be careful though, don't touch aerial when radiating 15w, thats quite a lot for just tuning an antenna. Also if your amp is homemade be sure its matched well to 50 ohm at the output by using a uhf dummy load (normal dummy loads/ resistors drop off in resistance at higher frequencies andDO NOT use wire wound resistors) and your swr meter between it and the amp.
((300/87.8)x0.935)x0.625=1.996 meters.
Because of the length the radiator will end up with capacitive component which you tune out using coil. Given your low frequency I would build the coil to Jans dimensions but with an extra turn/ half turn, then using your swr meter stretch/ compress/ trim the coil to minimum reflected power on the meter. Calculate the radials with same formula but instead of 0.625 multiply by 0.25.
Be careful though, don't touch aerial when radiating 15w, thats quite a lot for just tuning an antenna. Also if your amp is homemade be sure its matched well to 50 ohm at the output by using a uhf dummy load (normal dummy loads/ resistors drop off in resistance at higher frequencies andDO NOT use wire wound resistors) and your swr meter between it and the amp.
Posted by: Junction
« on: July 20, 2011, 11:42:02 am »OK, starting to make a bit more sense now. I'm want mine to operate on 87.8 Mhz, I have a SWR Meter, but my using a 15Watt Transmitter which I built myself using your 1Watt design and PLL and the output stage is a MRF1946, which works very well.
I can get more power but I think its always best to run your output stage slightly lower than its maximum performance.
Please can you show me an example of the formula using 87.8 Mhz also the correct wire size I need for 15watts on the coil section.
Thank you again Jan
I can get more power but I think its always best to run your output stage slightly lower than its maximum performance.
Please can you show me an example of the formula using 87.8 Mhz also the correct wire size I need for 15watts on the coil section.
Thank you again Jan
Posted by: Jan
« on: July 19, 2011, 08:39:51 am »λ is a wave length (299 cm on 100 MHz). You always need a SWR meter to tune the coil.
Posted by: Junction
« on: July 18, 2011, 09:28:53 pm »Please can someone help me with the Translation on this. I've done most of it but there's still a few things i don't get.
like this Symbol λ , am i dividing the Frequency by this 0,563λ .
In the Picture the translated text written on the left reads
Coil:
15 Thread wire
Dia 1.6mm to
average 8mm
Please Help Me Jan
like this Symbol λ , am i dividing the Frequency by this 0,563λ .
In the Picture the translated text written on the left reads
Coil:
15 Thread wire
Dia 1.6mm to
average 8mm
Please Help Me Jan