23cm aerial
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This forum is run by the BATC (British Amateur Television Club), it is service made freely available to all interested parties, please do not abuse this privilege.
Thank you
Re: 23cm aerial
I see the second attached plot (of Dave's JVL model) has vanished. Seems tot be a feature of this bulleting board for me. Here it is again.
- Attachments
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- JVL-lp.png (16.83 KiB) Viewed 2659 times
Re: 23cm aerial
A few months late I realise but I've just been trawling back through this thread. I have to admit to smiling at the attempts to make a good quad loop Yagi for 2 cms . I made several without much success in fact I just threw one away that I made years ago. You have to be very accurate with your dimensions and spacing of the elements to determine where in the band you want to use it. Essentially I found it to have a very narrow bandwidth.
The grid antenna I mentioned earlier I found to be far easier to make and it has a wider bandwidth. By its very nature it does unfortunately have strong side lobes but depending on whether you place the bays as x 4 horizontally or as two bays over two bays you can reduce the lobes. Having lobes isn't a bad thing as such especially with so few ATV signals about. Many times I have detected signals off to one side of the direction the antennas is pointing. A loop yagi would have missed them. As far as I recall my 4 bay array has about 24 Db gain. Having tuned each bay to an SWR of around 1.3 to one I use a 4 way splitter to match the bays into 50 Ohms Ecoflex low loss coax. The combined SWR measured at the transmitter is between 1.5 and 1.7 to one at around 1248 Mhz.
I have one antenna for TX and another tuned slightly further up the band for RX. Both antennas worked first time and have done stirling service for almost 20 years after much head scratching with quad loops and yagi's with little success.
Pete G8JAN
The grid antenna I mentioned earlier I found to be far easier to make and it has a wider bandwidth. By its very nature it does unfortunately have strong side lobes but depending on whether you place the bays as x 4 horizontally or as two bays over two bays you can reduce the lobes. Having lobes isn't a bad thing as such especially with so few ATV signals about. Many times I have detected signals off to one side of the direction the antennas is pointing. A loop yagi would have missed them. As far as I recall my 4 bay array has about 24 Db gain. Having tuned each bay to an SWR of around 1.3 to one I use a 4 way splitter to match the bays into 50 Ohms Ecoflex low loss coax. The combined SWR measured at the transmitter is between 1.5 and 1.7 to one at around 1248 Mhz.
I have one antenna for TX and another tuned slightly further up the band for RX. Both antennas worked first time and have done stirling service for almost 20 years after much head scratching with quad loops and yagi's with little success.
Pete G8JAN
Re: 23cm aerial
All very interesting. I guess 23/24cms ATV antennas are an art form they may look good but performance may vary!
I also notice that the links to images I added have vanished although they are still in my dropbox.
Maybe its to do with external links to images. So is there a way to upload images onto the forum so they dont dissappear?
A Picture tells a thousand words!
Cheers Mark
I also notice that the links to images I added have vanished although they are still in my dropbox.
Maybe its to do with external links to images. So is there a way to upload images onto the forum so they dont dissappear?
A Picture tells a thousand words!
Cheers Mark
Re: 23cm aerial
Hi Mark
Suggest we transfer the info you want to the wiki on this page: https://wiki.batc.org.uk/23cms_antennaes
73
Noel
Suggest we transfer the info you want to the wiki on this page: https://wiki.batc.org.uk/23cms_antennaes
73
Noel