Re: KST and /P


Filtering should be relatively easy, I suspect that a simple  high pass  will do (a notch at 70cm a poor  second choice)
Minicircuits do a range of high and low pass filters at reasonable prices (about £35  if i recall)
Building such a filter say 800MHz High Pass, should be relatively easy although attention to component size and  quality (use SMD caps and inductors) and good layout will be needed to achieve a low through loss at 2100MHz
Plenty of websites that will allow you to calculate the component values
If you need such a filter testing I have sweeping testgear available

Sent: Sunday, December 24, 2017 10:57 AM
Subject: [ukmicrowaves] KST and /P

I have been investigating further why access to KST is so poor when operating portable from hilltops. There was a discussion in this group earlier this year that concluded that the main problem was the mobile phone router hearing too many access points. However, while this is true I have found that the performance of both of my mobile routers is significantly worse under the following conditions:
Proximity to a PMR site
Use of 2m and particularly 70cms for talkback
Proximity to our 70cms analogue and digital repeaters
In the worse case the router actually crashes when subjected to high power RF.
Both of my routers use the Telit HE910-D to access the mobile phone system and I note no external RF filtering, the two aerials connect directly to the package. Can anyone point me to any documentation on the RF performance of this unit, particulalrly the characteistics of any RF filtering that may be incorporated. There are a number of documents on the digital interfacing, but have found none on the RF performance.
Since the unit covers 850-2100 MHz I suspect there may only be a combination of HPF and LPF to define the band.
Is anyone aware of a commercially available filter to improve out of band rejection of such a device. Are there filter designs that can be built to improve out of band rejection or to introduce a notch at 70cms?

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