SYNTECH II 70-0520CWB issues

[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

[jim202]

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]

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



Here's a schematic of the filter.



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]

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



Here's a schematic of the filter.



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