SYNTECH II 70-0520CWB issues

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willbartlett
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Location: Boston, MA

SYNTECH II 70-0520CWB issues

Post by willbartlett » Tue Nov 08, 2005 12:52 am

Hi ALl. I have a batch of these, and I have been digging through the schematics and comparing the PA assembly to the C model. A little background. The CWB Syntech II is a 37-48 MHZ radio, It has 2 seperate VCO's per tx and rx. I have everything but the PA happy in the 52-53mhz range. Power falloff is prety steep above 50 mhz. ANyone had any luck converting these?

Thanks, Will

jim202
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Joined: Sat Mar 29, 2003 9:47 am
Location: New Orleans region

Re: SYNTECH II 70-0520CWB issues

Post by jim202 » Fri Nov 11, 2005 9:47 am

By any chance is the output filter causing your output power to fall off? Many of the low band radios have the output lowpass filter skirts designed so that they roll off real fast after the 50 MHz point. You may end up having to modify the filter to allow a higher rolloff point.

Jim



[quote="willbartlett"]Hi ALl. I have a batch of these, and I have been digging through the schematics and comparing the PA assembly to the C model. A little background. The CWB Syntech II is a 37-48 MHZ radio, It has 2 seperate VCO's per tx and rx. I have everything but the PA happy in the 52-53mhz range. Power falloff is prety steep above 50 mhz. ANyone had any luck converting these?

Thanks, Will[/quote]

willbartlett
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Posts: 85
Joined: Wed Jan 23, 2002 8:00 pm
Location: Boston, MA

Post by willbartlett » Fri Nov 11, 2005 11:36 am

Well, I swept the filter with the network analyzer, and while modelling the filter as specified using rfsim99 shows a falloff around 52 mhz.

Image

Here's a schematic of the filter.

Image

the true response on the analyzer looks like it falls off up near 64-65 mhz, But I'll take another look.

Good thought, it wouldn't be too tough to mod the filter. I suspect the issue is with the PA section tho....


Will

WB5ITT
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Joined: Tue Jan 01, 2008 3:36 pm

Re:

Post by WB5ITT » Tue Jan 01, 2008 3:48 pm

willbartlett wrote:Well, I swept the filter with the network analyzer, and while modelling the filter as specified using rfsim99 shows a falloff around 52 mhz.

Image

Here's a schematic of the filter.

Image

the true response on the analyzer looks like it falls off up near 64-65 mhz, But I'll take another look.

Good thought, it wouldn't be too tough to mod the filter. I suspect the issue is with the PA section tho....


Will
All this was recently discussed on the MidlandLMR list at Yahoogroups.....yes, you should remove one turn from the LP filter coils to imprive % and output.

Chris
WB5ITT

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