Hello all,
Unfortunately it's not one transmitter, but four of them (I thought 5, but I just checked. Powers range from 1 - 10 kW), producing a lot of spurious signals and raising the noise floor by about 10 dB when pointing the beam into that direction. I don't think stubs will be broad enough to cover 89 to 106 MHz, but I never worked with them, so I'm guessing here. I don't have any problems with FM stations leaking onto 70 cm, just the air band, NOAA frequencies and 2 meters. My Airspy mini also picks up lots of spurious signals below 50 MHz, often hard enough to ID.
I found this filter from Par Electronics (http://www.parelectronics.com/fm-broadcast.php), but it doesn't indicate if you can tx through it. Otherwise I will have to use it in the shack and remove it when I want to tx on 2m, with the risk of forgetting it and blowing it up. Will a sequencer be a solution then?
73 de Hans
BX2ABT
On 03/15/2019 09:42 PM, Robert Bruninga wrote:
And you can make it without all the connectors at the T if you want. Though it takes some close and inventive soldering of the "T". Since the FM band is 88 to 108 that (I think) is far enough from 145 to add minimum loss. But at UHF, one needs to carefully check to make sure that the FM frequency is not also a multiple of the FM frequency.
Tell us the FM broadcast frequency and we can take a quick look.
Bob
-----Original Message----- From: AMSAT-BB [email protected] On Behalf Of Wendy and Terry Osborne Sent: Thursday, March 14, 2019 11:50 PM To: [email protected]; Hans BX2ABT [email protected] Subject: Re: [amsat-bb] Shoppinglist
Hi Hans,
If you have a plenty of RG213 and suitable connectors, you could try making a Coax stub filter. You need a cable length that is an odd multiple of a quarter wave length long at the FM Tx frequency and an even multiple of a quarter wave at the frequency that you want (2M /70CMs). A single RG213 stub would have about 25dB of rejection and would pass 100 Watts OK. You just need a coax T connector and some matching connectors. To trim the stub, use a set of garden secateurs. If you have a Bao feng or similar radio you could use that on the FM band attached to your T and trim the stub for minimum signal on the unwanted Tx frequency.
I haven't run the calculations for how long the stub should be but if it's useful I could do so.
73, Terry Osborne ZL2BAC
-----Original Message----- From: Hans BX2ABT Sent: Thursday, March 14, 2019 12:33 AM To: [email protected] Subject: [amsat-bb] Shoppinglist
My sis-in-law will be visiting from the States soon and I usually make her bring some stuff for me so I can save on freight costs. She will definitely bring an Arrow Antenna so I can start some portable operations. A Sony voice recorder is also on my list, as well as some coax cable (RG-400 is what I'm thinking of. Really expensive here). Don't have a budget for much more, but since I have a clear line-of-sight to some 10 kW FM transmitters from my QTH I thought I should at least get a good FM-band notch filter.
Any recommendations on where to buy this in the US? I haven't found anything when I googled, not even a lot of 2/70 band pass filters, or low pass filters to prevent desensing on 70 cm. My own creations have a too high insertion loss, so this time I really want something a bit more professional and something that can handle at least 100 Watts of power. Any recommendations are welcome. Cheers. --Hans BX2ABT
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Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb