Posts by PA1EW

    Ed,


    Did you detect any reduction of Rx or Tx signal because of the PP box. This is a very good idea: there are many different sizes of box available.


    73 Mike G4CDF

    Mike,

    The upside-down cheap food-box is made of Polypropylene PP5 and after being microwaved with >500W RF:) it stayed cool! (however, it has no microwave safe mark. This plastic is very sturdy, so sawing-drilling is easy. Only made RL-measurements with the "boxed" Helical feed in the feedpoint of a dish, measured abt 25dB at 2400MHz.

    Performance with my current 1.1m offset dish and abt. 3W at the Helix is very good, but could still be interesting to measure for any reduction on 2.4GHz and also for 10.5GHz using this type of weather-protection. I will come back on this.


    73 Ed PA1EW


    Update: I did test today using the PP5 plastic lid from the box. Placed in front of my LNB and checking the lower beacon I could not detect any signal reduction!. So 10.5GHz seems not bothered by polypropylene 5 plastic sheet, at least very little.

    An advantage of the upside-down box is that there is no condensation problem with the open underside.

    ... and talking about GPSDO's. I had a look at the spectrum from my mini-GPSDO Leo Bodnar and decided it would be good to add some low-pass filtering.

    The programmable LO unit works perfectly and I did not test without the 30MHz filter.

    As I use only a very short coaxial connection I also added a 10dB attenuator, so the LO-input with lowest setting of 8mA to the LNB is abt -3dBm.

    EDIT: This now proofed to be too much attenuation as the lock sometime was lost.

    I found Andy's G4JNT recommandation for 27MHz LO-output level at 0dBm ... +5dBm, so for test I took out the 10dB attenuator --> now abt +7dBm injected at the 2nd port of the Octagon with the lowest setting of 8mA in the mini-GPSDO.


    73 Ed PA1EW

    I am using here the same Octagon Twin OTSLO with 2nd output modified for GPSDO input 27,841846MHz just using a second coax and producing an IF of 435MHz with kHz the same as on the SAT downlink. All experimental setup with GPSDO outside next to the RX-dish (weatherproofed).

    Modification after all was very easy. No problem when you even remove the x-tal without de-soldering. In my case it ripped-off when trying to use a Dremel tool. The large solderpads are not used and very simple adding a 1nF chip-C for DC blocking, a 51 ohm load* and a short enamelled (isolated) copper CUL wire as shown.

    A small notch needs to be made in the cover part, preventing the wire getting pinched-off....


    *IMPORTANT UPDATE: My modified LNB lately suffered from sensitivity issue at startup. I finally did find out that the 50 ohms load was placed wrongly (as seen on last picture). The RDA3565 PLL circuit was possibly loaded too much with the 50 ohm (DC-)connected directly to the PLL-pin. Solution was to remove the 50 ohm, because the feeding coax is very short in my case. See the second picture with only extra C = 10nF that provides correct operation!.


    When a 50 ohm load is needed, please change the place of the DC-decoupling C AFTER the load, seen from the input. This is visible in several other modifications.

    Apologies, to whom following my initial pictures for modification...


    73 Ed PA1EW

    Hi, I recently joined the Forum.

    Another classic and robust Power-SWR meter that proofs to be useful at 2.4GHz is the R&S NAS + NAS-Z7 Directional Coupler. I was pleasantly surprised that the detachable Z7 head, used for servicing 1800-1900MHz networks, seemed to be quite accurate on 2.4GHz. Rated power is 30W and PEP indication works OK with SSB!.


    I used this meter mostly combined with a NAS-Z5 (25-1000MHz) coupler mainly on 2m - 70cm and did get a Z7 coupler cheaply with another unit on a flea-market. Glad that I did not get rid of the Z7!.


    You may find the battery-operated NAS + Z7 combo at flea-markets at reasonable prices and in time can upgrade with other couplers from the NAS series. It is wise to check the inside battery-compartment for corrosion...