MMDS Antennas

RG59

Are the MMDS mesh type antennas capabile of transmitting? What frequencies do they work on?

watty

two types.
1) The older one with a box at back
2) The newer ones with electronics in stalk on dish.

1) The box at back is an LNB 2.5GHz in and 200..420MHz out. Disconnect the N-Connector and any 2.4GHz / 2.5GHz 50Ohm transmitter or wireless lan card or video sender will work, perhaps up to 5km line of sight.


2) Don't know how easy it is to unplug the newer kind (beleived to have UHF IF rather than the olf VHF/Hyperband IF) LNB out of the stalk.
If any one has one they want to give me I'll experiment...

Analog MMDS may have type (1) or (2). Digital MMDS is always (2).

Unlike Sky LNB which has 4 modes, the LNB has no 22Khz band switch nor 14V/18V polarity switch.

The old ones seem to need a regulated 3/4 amp (750mA) at least 12V DC power. Feeding this up to LNB via isolate capacitor to TV and coil to Power unit gives Analog MMDS pictures on a TV of any unscrambled channels (C4, TV3 and Chorus / Bravo/H&L were the 3 clear channels on Woodcock hill last time I looked). An old Sky Analog ADX+ channel extender in "plus" mode shifts the channels up by 500MHz allowing a UHF only TV to tune all the MMDs channels. Any proper Irish TV /VHS should have the VHF/ hyperband needed to tune directly (Cable TV frequencies).

The analog MMDS is horrid. It is US NTSC cable TV settop boxes and gear connected to a microwave system that should have had FM PAL, but has AM PAL on it. Analog MMDS could have been much better but it was built out of stuff obsolete then and not engineered to a proper standard (i.e. FM transmission and Analog Satellite type PAL / Europe / Aus PAL FM MMDS settop boxes instead of rubbish US NTSC cable descrambler boxes).

US TV used to be 25 years behind us technically. Now it's only ten...

RG59

Are the two types different looking? i noticed some ones with a more circular type shape and a wider mesh.

watty

There are many patterns of dish.

Old Type:
Box at back of dish anyplace, maybe even below dish is about 7" x 5" x 3" approx.

Slightly bulbous but flattened plastic housing for dipole on end of stalk. Thinish vertical profile

Side view

      <>=====| rear of Dish
dipole  stalk

New Type:
No visible LNB box (LNB is inside the stalk)
Slight taper at tip of stalk
Flat metal horizontal dipole at end of stalk on its edge rather than flat as in old type

Side view

       |=====| rear of Dish
dipole  stalk

Dish and pole not shown on diagram, but at Right Hand Side. LHS pointing in direction of transmitter.


Dishes / LNB are property of Chorus /NTL. But if MMDS cancelled some years ago and dish still there they are unlikely to be looking for it.

They are rarely removed on cancelled sub due to labour cost, and I suppose hope that user will resubscribe.

In contrast a Sky subscriber owns Digibox, Dish and LNB and receives 60 odd Radio and many good TV even when cancelled.

Mike 1972

US TV used to be 25 years behind us technically. Now it's only ten

on the other hand American broadcasters are experimenting with HDTV transmission wheras in Europe it isint even on the agenda

Of course while it could be argued theres more need for HDTV in the US (because their analouge system is so awful) In an ironic and historic reversal of policy The Americans have decided that digital TV should be primarially about delivering higher quality wheras in Europe its all about more channels

Antenna

Watty,
I have one of those downconverters with integrated dipole aerial (the dipole enclosed by white plastic) you mention (from a storm damaged MMDS aerial - it snapped off!) but the output is Hyperband (not UHF), I have reproduced what its labels say below.

Now maybe there is more than one type of these with some using UHF as the I.F.??? Are you absolutely sure that some use UHF for I.F.?
I fail to see what advantage using UHF (opposed to Hyperband) as the I.F. would be - with UHF there would be more loss in the cable (important issue with long cable runs), also more risk of interference (from ingress of strong UHF TV signals to the downlead)

The physically broken MMDS block downconverter I have is labelled:

TranSystem, Inc
Made in Taiwan.

RF = 2500-2686 MHz
IF= 214 - 400MHz
Gain = 30dB

(The output is a ‘F’ socket)

watty

The LNB output is typically at a higher level than UHF TV.

Satellite LNBs convert from 10,500 MHz to 12,700MHz in to 750MHz to 2100MHz out (22KHz selects above or below 11,700MHz on input).

It was a Chorus MMDS installer told me about UHF o/p models. But he could be wrong or there could be two or more types of stalk kind.

The Sagem Digital MMDS box is similar to a DTT or Satellite Digital receiver (470MHz..890MHz DTT and 750MHz ... 2100MHz Digital Satellite Receiver) or possibly Cable TV Digital (210MHz to 460MHz).

All Digital receivers are similar but incompatible across Cable/DTT/Satellite.

It on the face of it would be logical if the Sagem used cable TV frequencies rather than UHF.

Never seen a Chorus Digital Cable box. How do they differ (if at all) from Digital MMDS box?

The output would be an F-Connector socket.

I have wondered to they work at C Band simply giving a higer o/p frequency (3500MHz to 4000MHz approx so o/p 1214 to 1700, feedable direct to SAT receiver ).
C-Band needs an awfull big dish though..

ozpass

The digital cable boxes are identical to the digital MMDS ones. The only difference is that they don't have a 'frequency convertor' inline with the input to the box. I'm not technical like yourself Watty so I'm not sure if frequency convertor is the correct name for it but it's a small (cheap looking) metallic silver box with its own power supply.