I'm building a Brick amp for 24cms using the RA18H1213G (30 Watts maximum).
Some sort of output filter is desirable and I found this https://www.marwynandjohn.org.uk/GM8OTI ... cmBPF.html which is within my build capability.
Is there any way of predicting its safe power handling? I assume, as its High-Q, that the capacitor end of the tuned rods will be very high voltage and so those capacitors will need to be 500V+ too.
But how high is high? If the voltage at 50 ohms is X, and the filter Q is 100, will the voltage be 100 * X?
Would something 'interdigital' work where the capacitors could be discs further way?
Advice or guidance welcome, (self training under way....)
Thanks
Gareth
24cms TX filter
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radiogareth
- Posts: 1233
- Joined: Wed Jan 06, 2016 9:46 am
Re: 24cms TX filter
And of course deeper googling and a rummage in the junk box/memory box produced a device labelled "G3GRO/1290" (Ex Crawley ARC and silent key 2016). Part of a big box full of stuff purchased at CATS 2018, it looks like a 3 pole interdigital, BNC in and out.
A quick run up on Satsagen shows a response curve every bit as sweet at the one on the BATC 24cms Filters page.
Question of power handling remains, what determines the rating??
I've also got several of the ex-70cms cavity filters mentioned for conversion. Could I make one of them into a Band pass rather than band-cut (notch)??
Gareth
A quick run up on Satsagen shows a response curve every bit as sweet at the one on the BATC 24cms Filters page.
Question of power handling remains, what determines the rating??
I've also got several of the ex-70cms cavity filters mentioned for conversion. Could I make one of them into a Band pass rather than band-cut (notch)??
Gareth
Re: 24cms TX filter
Gareth
Your filter sounds very much like the one I have. I bought mine direct from the chap that made it and sold them at the Kempston Rally about 30 years ago. It's constructed from copper bar and sheet with brass tuning screws and BNC connectors.
The design came from a 1980s Radio Communication handbook and was also printed one of the VHF/UHF Handbooks.
It will easily handle the power from a RA18H1213G in DATV use as that brick can only produce 3W RMS if the shoulders are to be kept to -40dBc or 6W with shoulders at -30dBc.
Clive G3GJA
Your filter sounds very much like the one I have. I bought mine direct from the chap that made it and sold them at the Kempston Rally about 30 years ago. It's constructed from copper bar and sheet with brass tuning screws and BNC connectors.
The design came from a 1980s Radio Communication handbook and was also printed one of the VHF/UHF Handbooks.
It will easily handle the power from a RA18H1213G in DATV use as that brick can only produce 3W RMS if the shoulders are to be kept to -40dBc or 6W with shoulders at -30dBc.
Clive G3GJA
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radiogareth
- Posts: 1233
- Joined: Wed Jan 06, 2016 9:46 am
Re: 24cms TX filter
Thanks Clive, This one does look 'home made' but very well home made and silver plated too.
Here is a satsagen plot of its characteristics. 'Good to go' I think.
Rather nice that I have another two of them so I can adjust for NB and perhaps use as RX filters too with a bit of gain.
Gareth
Here is a satsagen plot of its characteristics. 'Good to go' I think.
Rather nice that I have another two of them so I can adjust for NB and perhaps use as RX filters too with a bit of gain.
- 23cmInterdigital.jpg (135.54 KiB) Viewed 2162 times