International  Radio Roofing Filters

At present a filter board is available for the FT1000MP / MkV / Field, and for the TenTec Orion. Work is under way for the IC765 (sorry not 756pro) and for the TenTec OmniVI series.

The "Roofing filter" is the first I.F. filter in a radio. It is intended to keep unwanted signals out of the signal path of the receiver.Some modern radios use a very high first IF (often in the 70 MHz region) so that general-coverage receive as well as ham-bands can be included. They also usually include FM as a mode option. This means that the roofing filter can be up to 25 KHz wide, effectively offering a barn-door for other unwanted signals to drive the other parts of the receiver. Manufacturers generally provide cheap ceramic filters at the high first IF. They have a poor shape factor and this makes the receiver work even harder as more signals get through. Earlier this year INRAD found a source which can provide GOOD filters at the high first I.F. They ran tests and a high-quality filter board using a 6-pole filter has been produced for the FT1000MP series. Look at the curve below to see what sort of improvement results. These curves are plots made by measuring the response from an unmodified MP Field with one equipped with the roofing filter board. The wider trace is the unmodified board, and the narrow is with the roofing filter. As well as a vastly narrowed bandwidth, there is a small increase in gain.

FILTER PRICING - £165 INCLUDING VAT

Some of the comments from customers are given below

"I have been doing A/B tests with the Orion and FT1000MP in crowded large interfering signal conditions. I must say the FT1000MP is doing a very excellent job - and earlier tests clearly showed the superiority of the Orion in those kinds of conditions."

During field day - "I could walk over to the other stations and hear the difference between the stock FT1000MP's and my INRAD-equipped FT1000MP. Does the roofing filter make a difference? YES! Does the roofing filter give me an advantage? YES!

Frequently asked questions

Can both the INRAD FT1000MP noise improvement kit and the roofing filter be fitted at the same time? No - they use the same space in the receiver. However the "K9AY mod" (reduces hiss) is included with the filter kit.

Will it defeat the noise blanker? No

Will I still be able to use wide band SSB and FM with this filter installed? Not with the main receiver - the filter is designed for regular SSB and narrower modes such as CW and the data modes.  The filter determines the overall bandwidth of the receiver which is now 4 KHz. However, the sub-receiver can still be used for the wider bandwidth modes.

Will there be an even narrower CW version? Not at present. Tolerances are tight at 70 MHz, and the available filter is still very effective on CW.

Is the board easy to install? For the original MP no soldering is required. For the Mk5 or Field you would need to fashion two main pins for the power supply to the filter. This is very easy to do and we can give you more information if you wish. Alternatively, we can fit the board to your radio.