EB5AGV's Neuwirth HMT SiO Page

Neuwirth HMT SiO

This page is devoted to an interesting radio test instrument, a Neuwirth Frequenzhubmesser HMT SiO

Quoting Hans F5VKP / HB9AQS:

That's an instrument to measure the frequency deviation of an FM signal, and the frequency ranges indicated show that it was used for the land mobile services. Such instruments used to be important to make sure that all the analog mobile FM radios of taxis and police and all those users were up to specs (particularly when they changed from 25 kHz channel spacing to 12,5 in Germany in the 1970s). Being used for type approval / certification, it must be a precision instrument, and the brand name indicates that it must have been expensive.
The scope will probably show the AF signal, to check for distortion.

I got it at eBay for little money. Adding up shipment from Germany to Spain, total price was below 50 Eur. It came with a brief User's Manual (dated 1969 with 1972 mods). Good thing is that it includes specs and schematics.

Here you have basic specifications:

Frequency bands:

Intermediate frequency:


Instrument as received

Here you have some pictures of the unit as it arrived (well, I took it out of the cabinet):

Complete front panel:

Neuwirth HMT SiO

Left side:


Right side:

Internal views:

I have checked the unit and it receives in 2m band (144-146MHz). Sensitivity is not too great, though. I think this is because it is not intended to be a receiver but a signal analyzer to cjeck transmitters. Anyway, connecting a 2m band antenna, I have been able to listen (and view in the tiny scope!) strong signals.

UHF band is not working properly; it just receives noise, so I need to check it.

I still need to translate manual and labels in the front panel as I don't understand yet all the functions of the unit. Any hint welcomed!

I plan to scan manual and schematics and put them online, as perhaps somebody else has a similar unit without docs.


To be written...
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